CPU2017 Flag Description
Dell Inc. PowerEdge R6525 (AMD EPYC 7713 64-Core Processor)
Compilers: AMD Optimizing C/C++ Compiler Suite
Base Compiler Invocation
-
- clang
![[user]](https://www.spec.org/auto/cpu2017/images/user.png)
- CC, LD
-
clang is a C compiler which encompasses preprocessing, parsing, optimization, code generation, assembly, and linking.
Depending on which high-level mode setting is passed, Clang will stop before doing a full link.
-
- flang
- FC, LD
-
flang is a Fortran compiler which encompasses parsing, optimization, code generation, assembly, and linking. Depending on
which high-level mode setting is passed, Flang will stop before doing a full link.
-
- flang
- FC, LD
-
flang is a Fortran compiler which encompasses parsing, optimization, code generation, assembly, and linking. Depending on
which high-level mode setting is passed, Flang will stop before doing a full link.
-
- clang
- CC
-
clang is a C compiler which encompasses preprocessing, parsing, optimization, code generation, assembly, and linking.
Depending on which high-level mode setting is passed, Clang will stop before doing a full link.
-
- clang++
- CXX, LD
-
clang++ C++ compiler which encompasses preprocessing, parsing, optimization, code generation, assembly, and linking.
Depending on which high-level mode setting is passed, Clang will stop before doing a full link.
-
- clang
- CC
-
clang is a C compiler which encompasses preprocessing, parsing, optimization, code generation, assembly, and linking.
Depending on which high-level mode setting is passed, Clang will stop before doing a full link.
-
- flang
- FC
-
flang is a Fortran compiler which encompasses parsing, optimization, code generation, assembly, and linking. Depending on
which high-level mode setting is passed, Flang will stop before doing a full link.
Peak Compiler Invocation
-
- clang
- CC, LD
-
clang is a C compiler which encompasses preprocessing, parsing, optimization, code generation, assembly, and linking.
Depending on which high-level mode setting is passed, Clang will stop before doing a full link.
-
- flang
- FC, LD
-
flang is a Fortran compiler which encompasses parsing, optimization, code generation, assembly, and linking. Depending on
which high-level mode setting is passed, Flang will stop before doing a full link.
-
- flang
- FC, LD
-
flang is a Fortran compiler which encompasses parsing, optimization, code generation, assembly, and linking. Depending on
which high-level mode setting is passed, Flang will stop before doing a full link.
-
- clang
- CC
-
clang is a C compiler which encompasses preprocessing, parsing, optimization, code generation, assembly, and linking.
Depending on which high-level mode setting is passed, Clang will stop before doing a full link.
-
- clang++
- CXX, LD
-
clang++ C++ compiler which encompasses preprocessing, parsing, optimization, code generation, assembly, and linking.
Depending on which high-level mode setting is passed, Clang will stop before doing a full link.
-
- clang
- CC
-
clang is a C compiler which encompasses preprocessing, parsing, optimization, code generation, assembly, and linking.
Depending on which high-level mode setting is passed, Clang will stop before doing a full link.
-
- flang
- FC
-
flang is a Fortran compiler which encompasses parsing, optimization, code generation, assembly, and linking. Depending on
which high-level mode setting is passed, Flang will stop before doing a full link.
Base Portability Flags
-
![[suite]](https://www.spec.org/auto/cpu2017/images/suite.png)
- EXTRA_PORTABILITY
-
This option is used to indicate that the host system's integers are 32-bits
wide, and longs and pointers are 64-bits wide. Not all benchmarks
recognize this macro, but the preferred practice for data model selection
applies the flags to all benchmarks; this flag description is a placeholder
for those benchmarks that do not recognize this macro.
-
- EXTRA_PORTABILITY
-
This option is used to indicate that the host system's integers are 32-bits
wide, and longs and pointers are 64-bits wide. Not all benchmarks
recognize this macro, but the preferred practice for data model selection
applies the flags to all benchmarks; this flag description is a placeholder
for those benchmarks that do not recognize this macro.
-
- EXTRA_PORTABILITY
-
This option is used to indicate that the host system's integers are 32-bits
wide, and longs and pointers are 64-bits wide. Not all benchmarks
recognize this macro, but the preferred practice for data model selection
applies the flags to all benchmarks; this flag description is a placeholder
for those benchmarks that do not recognize this macro.
-
-
-
- EXTRA_PORTABILITY
-
This option is used to indicate that the host system's integers are 32-bits
wide, and longs and pointers are 64-bits wide. Not all benchmarks
recognize this macro, but the preferred practice for data model selection
applies the flags to all benchmarks; this flag description is a placeholder
for those benchmarks that do not recognize this macro.
-
-
- EXTRA_PORTABILITY
-
This option is used to indicate that the host system's integers are 32-bits
wide, and longs and pointers are 64-bits wide. Not all benchmarks
recognize this macro, but the preferred practice for data model selection
applies the flags to all benchmarks; this flag description is a placeholder
for those benchmarks that do not recognize this macro.
-
-
-
- EXTRA_PORTABILITY
-
This option is used to indicate that the host system's integers are 32-bits
wide, and longs and pointers are 64-bits wide. Not all benchmarks
recognize this macro, but the preferred practice for data model selection
applies the flags to all benchmarks; this flag description is a placeholder
for those benchmarks that do not recognize this macro.
-
- EXTRA_PORTABILITY
-
This option is used to indicate that the host system's integers are 32-bits
wide, and longs and pointers are 64-bits wide. Not all benchmarks
recognize this macro, but the preferred practice for data model selection
applies the flags to all benchmarks; this flag description is a placeholder
for those benchmarks that do not recognize this macro.
-
- EXTRA_PORTABILITY
-
This option is used to indicate that the host system's integers are 32-bits
wide, and longs and pointers are 64-bits wide. Not all benchmarks
recognize this macro, but the preferred practice for data model selection
applies the flags to all benchmarks; this flag description is a placeholder
for those benchmarks that do not recognize this macro.
-
- EXTRA_PORTABILITY
-
This option is used to indicate that the host system's integers are 32-bits
wide, and longs and pointers are 64-bits wide. Not all benchmarks
recognize this macro, but the preferred practice for data model selection
applies the flags to all benchmarks; this flag description is a placeholder
for those benchmarks that do not recognize this macro.
-
- EXTRA_PORTABILITY
-
This option is used to indicate that the host system's integers are 32-bits
wide, and longs and pointers are 64-bits wide. Not all benchmarks
recognize this macro, but the preferred practice for data model selection
applies the flags to all benchmarks; this flag description is a placeholder
for those benchmarks that do not recognize this macro.
Peak Portability Flags
-
- EXTRA_PORTABILITY
-
This option is used to indicate that the host system's integers are 32-bits
wide, and longs and pointers are 64-bits wide. Not all benchmarks
recognize this macro, but the preferred practice for data model selection
applies the flags to all benchmarks; this flag description is a placeholder
for those benchmarks that do not recognize this macro.
-
- EXTRA_PORTABILITY
-
This option is used to indicate that the host system's integers are 32-bits
wide, and longs and pointers are 64-bits wide. Not all benchmarks
recognize this macro, but the preferred practice for data model selection
applies the flags to all benchmarks; this flag description is a placeholder
for those benchmarks that do not recognize this macro.
-
- EXTRA_PORTABILITY
-
This option is used to indicate that the host system's integers are 32-bits
wide, and longs and pointers are 64-bits wide. Not all benchmarks
recognize this macro, but the preferred practice for data model selection
applies the flags to all benchmarks; this flag description is a placeholder
for those benchmarks that do not recognize this macro.
-
-
-
- EXTRA_PORTABILITY
-
This option is used to indicate that the host system's integers are 32-bits
wide, and longs and pointers are 64-bits wide. Not all benchmarks
recognize this macro, but the preferred practice for data model selection
applies the flags to all benchmarks; this flag description is a placeholder
for those benchmarks that do not recognize this macro.
-
-
- EXTRA_PORTABILITY
-
This option is used to indicate that the host system's integers are 32-bits
wide, and longs and pointers are 64-bits wide. Not all benchmarks
recognize this macro, but the preferred practice for data model selection
applies the flags to all benchmarks; this flag description is a placeholder
for those benchmarks that do not recognize this macro.
-
-
-
- EXTRA_PORTABILITY
-
This option is used to indicate that the host system's integers are 32-bits
wide, and longs and pointers are 64-bits wide. Not all benchmarks
recognize this macro, but the preferred practice for data model selection
applies the flags to all benchmarks; this flag description is a placeholder
for those benchmarks that do not recognize this macro.
-
- EXTRA_PORTABILITY
-
This option is used to indicate that the host system's integers are 32-bits
wide, and longs and pointers are 64-bits wide. Not all benchmarks
recognize this macro, but the preferred practice for data model selection
applies the flags to all benchmarks; this flag description is a placeholder
for those benchmarks that do not recognize this macro.
-
- EXTRA_PORTABILITY
-
This option is used to indicate that the host system's integers are 32-bits
wide, and longs and pointers are 64-bits wide. Not all benchmarks
recognize this macro, but the preferred practice for data model selection
applies the flags to all benchmarks; this flag description is a placeholder
for those benchmarks that do not recognize this macro.
-
- EXTRA_PORTABILITY
-
This option is used to indicate that the host system's integers are 32-bits
wide, and longs and pointers are 64-bits wide. Not all benchmarks
recognize this macro, but the preferred practice for data model selection
applies the flags to all benchmarks; this flag description is a placeholder
for those benchmarks that do not recognize this macro.
-
- EXTRA_PORTABILITY
-
This option is used to indicate that the host system's integers are 32-bits
wide, and longs and pointers are 64-bits wide. Not all benchmarks
recognize this macro, but the preferred practice for data model selection
applies the flags to all benchmarks; this flag description is a placeholder
for those benchmarks that do not recognize this macro.
Base Optimization Flags
-
- -m64
- CC, LD
-
Generate code for a 64-bit environment. The 64-bit environment sets int to 32 bits and long and
pointer to 64 bits and generates code for AMD's x86-64 architecture. The compiler generates AMD64, INTEL64,
x86-64 64-bit ABI. The default on a 32-bit host is 32-bit ABI. The default on a 64-bit host is 64-bit ABI if the target
platform specified is 64-bit, otherwise the default is 32-bit.
-
-
-
-
-
-
-
- -O3
- COPTIMIZE
-
Like -O2, except that it enables optimizations that take longer to perform or that may generate larger code (in
an attempt to make the program run faster).
If multiple "O" options are used, with or without level numbers, the last such option is the one that is effective.
- Includes:
-
- -march=znver3
- COPTIMIZE
-
Specify that Clang should generate code for a specific processor family member and later. For example, if you specify
-march=znver1, the compiler is allowed to generate instructions that are valid on AMD Zen processors, but
which may not exist on earlier products.
-
-
- -ffast-math
- COPTIMIZE
-
Enables a range of optimizations that provide faster, though sometimes less precise, mathematical operations that may
not conform to the IEEE-754 specifications. When this option is specified, the __STDC_IEC_559__ macro is
ignored even if set by the system headers.
-
-
- -fstruct-layout=5
- COPTIMIZE
-
Analyzes the whole program to determine if the structures in the code can be peeled and if pointer or integer fields in
the structure can be compressed. If feasible, this optimization transforms the code to enable these improvements. This
transformation is likely to improve cache utilization and memory bandwidth. This, in turn, is expected to improve the
scalability of programs executed on multiple cores.
This is effective only under -flto as whole program analysis is required to perform this optimization. You can choose
different levels of aggressiveness with which this optimization can be applied to your application with 1 being the least
aggressive and 7 being the most aggressive level.
Possible values:
- fstruct-layout=1: enables structure peeling.
- fstruct-layout=2: enables structure peeling and selectively compresses self-referential pointers in these
structures to 32-bit pointers wherever safe.
- fstruct-layout=3: enables structure peeling and selectively compresses self-referential pointers in these
structures to 16-bit pointers wherever safe.
- fstruct-layout=4: enables structure peeling, pointer compression as in level 2 and further enables
compression of structure fields which are of integer type. This is performed under a strict safety check.
- fstruct-layout=5: enables structure peeling, pointer compression as in level 3 and further enables compression
of structure fields which are of integer type. This is performed under a strict safety check.
- fstruct-layout=6: enables structure peeling, pointer compression as in level 2 and further enables compression
of structure fields which are of type 64-bit 'signed int' or 'unsigned Int'. The user needs to ensure that the values
assigned to 64-bit 'signed int' fields are in range -(2^31 - 1) to +(2^31 - 1) and 64-bit 'unsigned int' fields are in
range 0 to +(2^31 - 1), otherwise, incorrect results may be obtained. This compression is performed without considering
any safety analysis and so the user needs to ensure the safety based on the program compiled.
- fstruct-layout=7: enables structure peeling, pointer compression as in level 3 and further enables compression
of structure fields which are of type 64-bit 'signed int' or 'unsigned Int'. The user needs to ensure that the values
assigned to 64-bit 'signed int' fields are in range -(2^31 - 1) to +(2^31 - 1) and 64-bit 'unsigned int' field are in
range 0 to +(2^31 - 1) , otherwise, incorrect results may be obtained. This compression is performed without considering
any safety analysis and so the user needs to ensure the safety based on the program compiled.
Note:
fstruct-layout=4 and fstruct-layout=5 are derived from fstruct-layout=2 and fstruct-layout=3 respectively with the added
feature of safe compression of integer fields in structures. Going from fstruct-layout=4 to fstruct-layout=5 may result
in higher performance if the pointer values are such that the pointers can be compressed to 16-bits.
fstruct-layout=6 and fstruct-layout=7 are derived from fstruct-layout=2 and fstruct-layout=3 respectively with the added
feature of compression of integer fields in structures. These are similar to fstruct-layout=4 and fstruct-layout=5, but
here, the integer fields of the structures are always compressed from 64-bits to 32-bits without any safety guarantee.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
- -m64
- FC, LD
-
Generate code for a 64-bit environment. The 64-bit environment sets int to 32 bits and long and
pointer to 64 bits and generates code for AMD's x86-64 architecture. The compiler generates AMD64, INTEL64,
x86-64 64-bit ABI. The default on a 32-bit host is 32-bit ABI. The default on a 64-bit host is 64-bit ABI if the target
platform specified is 64-bit, otherwise the default is 32-bit.
-
-
-
-
-
-
-
-
-
-
- -O3
- FOPTIMIZE
-
Like -O2, except that it enables optimizations that take longer to perform or that may generate larger code (in
an attempt to make the program run faster).
If multiple "O" options are used, with or without level numbers, the last such option is the one that is effective.
- Includes:
-
- -march=znver3
- FOPTIMIZE
-
Specify that Clang should generate code for a specific processor family member and later. For example, if you specify
-march=znver1, the compiler is allowed to generate instructions that are valid on AMD Zen processors, but
which may not exist on earlier products.
-
-
- -ffast-math
- FOPTIMIZE
-
Enables a range of optimizations that provide faster, though sometimes less precise, mathematical operations that may
not conform to the IEEE-754 specifications. When this option is specified, the __STDC_IEC_559__ macro is
ignored even if set by the system headers.
-
- -Mrecursive
- FOPTIMIZE
-
Allocate local variables on the stack, thus allowing recursion.
SAVEd, data-initialized, or namelist members are always allocated
statically, regardless of the setting of this switch.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
- -m64
- CC, FC, LD
-
Generate code for a 64-bit environment. The 64-bit environment sets int to 32 bits and long and
pointer to 64 bits and generates code for AMD's x86-64 architecture. The compiler generates AMD64, INTEL64,
x86-64 64-bit ABI. The default on a 32-bit host is 32-bit ABI. The default on a 64-bit host is 64-bit ABI if the target
platform specified is 64-bit, otherwise the default is 32-bit.
-
-
-
-
-
-
-
-
-
- -O3
- COPTIMIZE, FOPTIMIZE
-
Like -O2, except that it enables optimizations that take longer to perform or that may generate larger code (in
an attempt to make the program run faster).
If multiple "O" options are used, with or without level numbers, the last such option is the one that is effective.
- Includes:
-
- -march=znver3
- COPTIMIZE, FOPTIMIZE
-
Specify that Clang should generate code for a specific processor family member and later. For example, if you specify
-march=znver1, the compiler is allowed to generate instructions that are valid on AMD Zen processors, but
which may not exist on earlier products.
-
-
- -ffast-math
- COPTIMIZE, FOPTIMIZE
-
Enables a range of optimizations that provide faster, though sometimes less precise, mathematical operations that may
not conform to the IEEE-754 specifications. When this option is specified, the __STDC_IEC_559__ macro is
ignored even if set by the system headers.
-
-
- -fstruct-layout=5
- COPTIMIZE
-
Analyzes the whole program to determine if the structures in the code can be peeled and if pointer or integer fields in
the structure can be compressed. If feasible, this optimization transforms the code to enable these improvements. This
transformation is likely to improve cache utilization and memory bandwidth. This, in turn, is expected to improve the
scalability of programs executed on multiple cores.
This is effective only under -flto as whole program analysis is required to perform this optimization. You can choose
different levels of aggressiveness with which this optimization can be applied to your application with 1 being the least
aggressive and 7 being the most aggressive level.
Possible values:
- fstruct-layout=1: enables structure peeling.
- fstruct-layout=2: enables structure peeling and selectively compresses self-referential pointers in these
structures to 32-bit pointers wherever safe.
- fstruct-layout=3: enables structure peeling and selectively compresses self-referential pointers in these
structures to 16-bit pointers wherever safe.
- fstruct-layout=4: enables structure peeling, pointer compression as in level 2 and further enables
compression of structure fields which are of integer type. This is performed under a strict safety check.
- fstruct-layout=5: enables structure peeling, pointer compression as in level 3 and further enables compression
of structure fields which are of integer type. This is performed under a strict safety check.
- fstruct-layout=6: enables structure peeling, pointer compression as in level 2 and further enables compression
of structure fields which are of type 64-bit 'signed int' or 'unsigned Int'. The user needs to ensure that the values
assigned to 64-bit 'signed int' fields are in range -(2^31 - 1) to +(2^31 - 1) and 64-bit 'unsigned int' fields are in
range 0 to +(2^31 - 1), otherwise, incorrect results may be obtained. This compression is performed without considering
any safety analysis and so the user needs to ensure the safety based on the program compiled.
- fstruct-layout=7: enables structure peeling, pointer compression as in level 3 and further enables compression
of structure fields which are of type 64-bit 'signed int' or 'unsigned Int'. The user needs to ensure that the values
assigned to 64-bit 'signed int' fields are in range -(2^31 - 1) to +(2^31 - 1) and 64-bit 'unsigned int' field are in
range 0 to +(2^31 - 1) , otherwise, incorrect results may be obtained. This compression is performed without considering
any safety analysis and so the user needs to ensure the safety based on the program compiled.
Note:
fstruct-layout=4 and fstruct-layout=5 are derived from fstruct-layout=2 and fstruct-layout=3 respectively with the added
feature of safe compression of integer fields in structures. Going from fstruct-layout=4 to fstruct-layout=5 may result
in higher performance if the pointer values are such that the pointers can be compressed to 16-bits.
fstruct-layout=6 and fstruct-layout=7 are derived from fstruct-layout=2 and fstruct-layout=3 respectively with the added
feature of compression of integer fields in structures. These are similar to fstruct-layout=4 and fstruct-layout=5, but
here, the integer fields of the structures are always compressed from 64-bits to 32-bits without any safety guarantee.
-
-
-
-
-
-
-
-
-
-
-
- -Mrecursive
- FOPTIMIZE
-
Allocate local variables on the stack, thus allowing recursion.
SAVEd, data-initialized, or namelist members are always allocated
statically, regardless of the setting of this switch.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
- -m64
- CC, CXX, FC, LD
-
Generate code for a 64-bit environment. The 64-bit environment sets int to 32 bits and long and
pointer to 64 bits and generates code for AMD's x86-64 architecture. The compiler generates AMD64, INTEL64,
x86-64 64-bit ABI. The default on a 32-bit host is 32-bit ABI. The default on a 64-bit host is 64-bit ABI if the target
platform specified is 64-bit, otherwise the default is 32-bit.
-
-
-
-
-
-
-
-
-
- -O3
- COPTIMIZE, CXXOPTIMIZE, FOPTIMIZE
-
Like -O2, except that it enables optimizations that take longer to perform or that may generate larger code (in
an attempt to make the program run faster).
If multiple "O" options are used, with or without level numbers, the last such option is the one that is effective.
- Includes:
-
- -march=znver3
- COPTIMIZE, CXXOPTIMIZE, FOPTIMIZE
-
Specify that Clang should generate code for a specific processor family member and later. For example, if you specify
-march=znver1, the compiler is allowed to generate instructions that are valid on AMD Zen processors, but
which may not exist on earlier products.
-
-
- -ffast-math
- COPTIMIZE, CXXOPTIMIZE, FOPTIMIZE
-
Enables a range of optimizations that provide faster, though sometimes less precise, mathematical operations that may
not conform to the IEEE-754 specifications. When this option is specified, the __STDC_IEC_559__ macro is
ignored even if set by the system headers.
-
-
- -fstruct-layout=5
- COPTIMIZE
-
Analyzes the whole program to determine if the structures in the code can be peeled and if pointer or integer fields in
the structure can be compressed. If feasible, this optimization transforms the code to enable these improvements. This
transformation is likely to improve cache utilization and memory bandwidth. This, in turn, is expected to improve the
scalability of programs executed on multiple cores.
This is effective only under -flto as whole program analysis is required to perform this optimization. You can choose
different levels of aggressiveness with which this optimization can be applied to your application with 1 being the least
aggressive and 7 being the most aggressive level.
Possible values:
- fstruct-layout=1: enables structure peeling.
- fstruct-layout=2: enables structure peeling and selectively compresses self-referential pointers in these
structures to 32-bit pointers wherever safe.
- fstruct-layout=3: enables structure peeling and selectively compresses self-referential pointers in these
structures to 16-bit pointers wherever safe.
- fstruct-layout=4: enables structure peeling, pointer compression as in level 2 and further enables
compression of structure fields which are of integer type. This is performed under a strict safety check.
- fstruct-layout=5: enables structure peeling, pointer compression as in level 3 and further enables compression
of structure fields which are of integer type. This is performed under a strict safety check.
- fstruct-layout=6: enables structure peeling, pointer compression as in level 2 and further enables compression
of structure fields which are of type 64-bit 'signed int' or 'unsigned Int'. The user needs to ensure that the values
assigned to 64-bit 'signed int' fields are in range -(2^31 - 1) to +(2^31 - 1) and 64-bit 'unsigned int' fields are in
range 0 to +(2^31 - 1), otherwise, incorrect results may be obtained. This compression is performed without considering
any safety analysis and so the user needs to ensure the safety based on the program compiled.
- fstruct-layout=7: enables structure peeling, pointer compression as in level 3 and further enables compression
of structure fields which are of type 64-bit 'signed int' or 'unsigned Int'. The user needs to ensure that the values
assigned to 64-bit 'signed int' fields are in range -(2^31 - 1) to +(2^31 - 1) and 64-bit 'unsigned int' field are in
range 0 to +(2^31 - 1) , otherwise, incorrect results may be obtained. This compression is performed without considering
any safety analysis and so the user needs to ensure the safety based on the program compiled.
Note:
fstruct-layout=4 and fstruct-layout=5 are derived from fstruct-layout=2 and fstruct-layout=3 respectively with the added
feature of safe compression of integer fields in structures. Going from fstruct-layout=4 to fstruct-layout=5 may result
in higher performance if the pointer values are such that the pointers can be compressed to 16-bits.
fstruct-layout=6 and fstruct-layout=7 are derived from fstruct-layout=2 and fstruct-layout=3 respectively with the added
feature of compression of integer fields in structures. These are similar to fstruct-layout=4 and fstruct-layout=5, but
here, the integer fields of the structures are always compressed from 64-bits to 32-bits without any safety guarantee.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
- -mllvm -aggressive-loop-unswitch
- CXXOPTIMIZE
-
This option enables aggressive loop unswitching heuristic (including -enable-partial-unswitch)
based on the usage of the branch conditional values. Loop unswitching leads to code-bloat. Code-bloat can be
minimized if the hoisted condition is executed more often. This heuristic prioritizes the conditions based
on the number of times they are used within the loop. The heuristic can be controlled with the following options:
- -unswitch-identical-branches-min-count=<n>
Enables unswitching of a loop with respect to a branch conditional value (B), where B appears in at least
<n> compares in the loop. This option is enabled with -aggressive-loop-unswitch. Default value is 3.
Usage: -mllvm -aggressive-loop-unswitch -mllvm -unswitch-identical-branches-min-count=<n>
where n is a positive integer and lower value of <n> facilitates more unswitching
- -unswitch-identical-branches-max-count=<n>
Enables unswitching of a loop with respect to a branch conditional value (B), where B appears in at most
<n> compares in the loop. This option is enabled with -aggressive-loop-unswitch. Default value is 6.
Usage: -mllvm -aggressive-loop-unswitch -mllvm -unswitch-identical-branches-max-count=<n>
where n is a positive integer and higher value of <n> facilitates more unswitching
Note: These options may facilitate more unswitching in some of the workloads. Since loop-unswitching inherently leads
to code bloat, facilitating more unswitching may significantly increase the code size and hence may also lead to longer
compilation times.
- Includes:
-
-
-
-
- -Mrecursive
- FOPTIMIZE
-
Allocate local variables on the stack, thus allowing recursion.
SAVEd, data-initialized, or namelist members are always allocated
statically, regardless of the setting of this switch.
-
-
-
-
-
-
-
-
-
-
-
-
Peak Optimization Flags
-
- -m64
- CC, LD
-
Generate code for a 64-bit environment. The 64-bit environment sets int to 32 bits and long and
pointer to 64 bits and generates code for AMD's x86-64 architecture. The compiler generates AMD64, INTEL64,
x86-64 64-bit ABI. The default on a 32-bit host is 32-bit ABI. The default on a 64-bit host is 64-bit ABI if the target
platform specified is 64-bit, otherwise the default is 32-bit.
-
-
-
-
-
-
-
- -march=znver3
- COPTIMIZE
-
Specify that Clang should generate code for a specific processor family member and later. For example, if you specify
-march=znver1, the compiler is allowed to generate instructions that are valid on AMD Zen processors, but
which may not exist on earlier products.
-
-
- -ffast-math
- COPTIMIZE
-
Enables a range of optimizations that provide faster, though sometimes less precise, mathematical operations that may
not conform to the IEEE-754 specifications. When this option is specified, the __STDC_IEC_559__ macro is
ignored even if set by the system headers.
-
-
- -fstruct-layout=5
- COPTIMIZE
-
Analyzes the whole program to determine if the structures in the code can be peeled and if pointer or integer fields in
the structure can be compressed. If feasible, this optimization transforms the code to enable these improvements. This
transformation is likely to improve cache utilization and memory bandwidth. This, in turn, is expected to improve the
scalability of programs executed on multiple cores.
This is effective only under -flto as whole program analysis is required to perform this optimization. You can choose
different levels of aggressiveness with which this optimization can be applied to your application with 1 being the least
aggressive and 7 being the most aggressive level.
Possible values:
- fstruct-layout=1: enables structure peeling.
- fstruct-layout=2: enables structure peeling and selectively compresses self-referential pointers in these
structures to 32-bit pointers wherever safe.
- fstruct-layout=3: enables structure peeling and selectively compresses self-referential pointers in these
structures to 16-bit pointers wherever safe.
- fstruct-layout=4: enables structure peeling, pointer compression as in level 2 and further enables
compression of structure fields which are of integer type. This is performed under a strict safety check.
- fstruct-layout=5: enables structure peeling, pointer compression as in level 3 and further enables compression
of structure fields which are of integer type. This is performed under a strict safety check.
- fstruct-layout=6: enables structure peeling, pointer compression as in level 2 and further enables compression
of structure fields which are of type 64-bit 'signed int' or 'unsigned Int'. The user needs to ensure that the values
assigned to 64-bit 'signed int' fields are in range -(2^31 - 1) to +(2^31 - 1) and 64-bit 'unsigned int' fields are in
range 0 to +(2^31 - 1), otherwise, incorrect results may be obtained. This compression is performed without considering
any safety analysis and so the user needs to ensure the safety based on the program compiled.
- fstruct-layout=7: enables structure peeling, pointer compression as in level 3 and further enables compression
of structure fields which are of type 64-bit 'signed int' or 'unsigned Int'. The user needs to ensure that the values
assigned to 64-bit 'signed int' fields are in range -(2^31 - 1) to +(2^31 - 1) and 64-bit 'unsigned int' field are in
range 0 to +(2^31 - 1) , otherwise, incorrect results may be obtained. This compression is performed without considering
any safety analysis and so the user needs to ensure the safety based on the program compiled.
Note:
fstruct-layout=4 and fstruct-layout=5 are derived from fstruct-layout=2 and fstruct-layout=3 respectively with the added
feature of safe compression of integer fields in structures. Going from fstruct-layout=4 to fstruct-layout=5 may result
in higher performance if the pointer values are such that the pointers can be compressed to 16-bits.
fstruct-layout=6 and fstruct-layout=7 are derived from fstruct-layout=2 and fstruct-layout=3 respectively with the added
feature of compression of integer fields in structures. These are similar to fstruct-layout=4 and fstruct-layout=5, but
here, the integer fields of the structures are always compressed from 64-bits to 32-bits without any safety guarantee.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
- -m64
- CC, LD
-
Generate code for a 64-bit environment. The 64-bit environment sets int to 32 bits and long and
pointer to 64 bits and generates code for AMD's x86-64 architecture. The compiler generates AMD64, INTEL64,
x86-64 64-bit ABI. The default on a 32-bit host is 32-bit ABI. The default on a 64-bit host is 64-bit ABI if the target
platform specified is 64-bit, otherwise the default is 32-bit.
-
-
-
-
-
-
- -march=znver3
- COPTIMIZE
-
Specify that Clang should generate code for a specific processor family member and later. For example, if you specify
-march=znver1, the compiler is allowed to generate instructions that are valid on AMD Zen processors, but
which may not exist on earlier products.
-
-
- -ffast-math
- COPTIMIZE
-
Enables a range of optimizations that provide faster, though sometimes less precise, mathematical operations that may
not conform to the IEEE-754 specifications. When this option is specified, the __STDC_IEC_559__ macro is
ignored even if set by the system headers.
-
-
- -fstruct-layout=5
- COPTIMIZE
-
Analyzes the whole program to determine if the structures in the code can be peeled and if pointer or integer fields in
the structure can be compressed. If feasible, this optimization transforms the code to enable these improvements. This
transformation is likely to improve cache utilization and memory bandwidth. This, in turn, is expected to improve the
scalability of programs executed on multiple cores.
This is effective only under -flto as whole program analysis is required to perform this optimization. You can choose
different levels of aggressiveness with which this optimization can be applied to your application with 1 being the least
aggressive and 7 being the most aggressive level.
Possible values:
- fstruct-layout=1: enables structure peeling.
- fstruct-layout=2: enables structure peeling and selectively compresses self-referential pointers in these
structures to 32-bit pointers wherever safe.
- fstruct-layout=3: enables structure peeling and selectively compresses self-referential pointers in these
structures to 16-bit pointers wherever safe.
- fstruct-layout=4: enables structure peeling, pointer compression as in level 2 and further enables
compression of structure fields which are of integer type. This is performed under a strict safety check.
- fstruct-layout=5: enables structure peeling, pointer compression as in level 3 and further enables compression
of structure fields which are of integer type. This is performed under a strict safety check.
- fstruct-layout=6: enables structure peeling, pointer compression as in level 2 and further enables compression
of structure fields which are of type 64-bit 'signed int' or 'unsigned Int'. The user needs to ensure that the values
assigned to 64-bit 'signed int' fields are in range -(2^31 - 1) to +(2^31 - 1) and 64-bit 'unsigned int' fields are in
range 0 to +(2^31 - 1), otherwise, incorrect results may be obtained. This compression is performed without considering
any safety analysis and so the user needs to ensure the safety based on the program compiled.
- fstruct-layout=7: enables structure peeling, pointer compression as in level 3 and further enables compression
of structure fields which are of type 64-bit 'signed int' or 'unsigned Int'. The user needs to ensure that the values
assigned to 64-bit 'signed int' fields are in range -(2^31 - 1) to +(2^31 - 1) and 64-bit 'unsigned int' field are in
range 0 to +(2^31 - 1) , otherwise, incorrect results may be obtained. This compression is performed without considering
any safety analysis and so the user needs to ensure the safety based on the program compiled.
Note:
fstruct-layout=4 and fstruct-layout=5 are derived from fstruct-layout=2 and fstruct-layout=3 respectively with the added
feature of safe compression of integer fields in structures. Going from fstruct-layout=4 to fstruct-layout=5 may result
in higher performance if the pointer values are such that the pointers can be compressed to 16-bits.
fstruct-layout=6 and fstruct-layout=7 are derived from fstruct-layout=2 and fstruct-layout=3 respectively with the added
feature of compression of integer fields in structures. These are similar to fstruct-layout=4 and fstruct-layout=5, but
here, the integer fields of the structures are always compressed from 64-bits to 32-bits without any safety guarantee.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
- -m64
- FC, LD
-
Generate code for a 64-bit environment. The 64-bit environment sets int to 32 bits and long and
pointer to 64 bits and generates code for AMD's x86-64 architecture. The compiler generates AMD64, INTEL64,
x86-64 64-bit ABI. The default on a 32-bit host is 32-bit ABI. The default on a 64-bit host is 64-bit ABI if the target
platform specified is 64-bit, otherwise the default is 32-bit.
-
-
-
-
-
-
-
-
-
- -march=znver3
- FOPTIMIZE
-
Specify that Clang should generate code for a specific processor family member and later. For example, if you specify
-march=znver1, the compiler is allowed to generate instructions that are valid on AMD Zen processors, but
which may not exist on earlier products.
-
-
- -ffast-math
- FOPTIMIZE
-
Enables a range of optimizations that provide faster, though sometimes less precise, mathematical operations that may
not conform to the IEEE-754 specifications. When this option is specified, the __STDC_IEC_559__ macro is
ignored even if set by the system headers.
-
- -Mrecursive
- FOPTIMIZE
-
Allocate local variables on the stack, thus allowing recursion.
SAVEd, data-initialized, or namelist members are always allocated
statically, regardless of the setting of this switch.
-
-
-
-
-
-
-
-
-
-
-
- -m64
- FC, LD
-
Generate code for a 64-bit environment. The 64-bit environment sets int to 32 bits and long and
pointer to 64 bits and generates code for AMD's x86-64 architecture. The compiler generates AMD64, INTEL64,
x86-64 64-bit ABI. The default on a 32-bit host is 32-bit ABI. The default on a 64-bit host is 64-bit ABI if the target
platform specified is 64-bit, otherwise the default is 32-bit.
-
-
-
-
-
-
-
-
-
- -march=znver3
- FOPTIMIZE
-
Specify that Clang should generate code for a specific processor family member and later. For example, if you specify
-march=znver1, the compiler is allowed to generate instructions that are valid on AMD Zen processors, but
which may not exist on earlier products.
-
-
- -ffast-math
- FOPTIMIZE
-
Enables a range of optimizations that provide faster, though sometimes less precise, mathematical operations that may
not conform to the IEEE-754 specifications. When this option is specified, the __STDC_IEC_559__ macro is
ignored even if set by the system headers.
-
-
- -Mrecursive
- FOPTIMIZE
-
Allocate local variables on the stack, thus allowing recursion.
SAVEd, data-initialized, or namelist members are always allocated
statically, regardless of the setting of this switch.
-
-
-
-
-
-
-
-
-
-
-
- -m64
- CC, FC, LD
-
Generate code for a 64-bit environment. The 64-bit environment sets int to 32 bits and long and
pointer to 64 bits and generates code for AMD's x86-64 architecture. The compiler generates AMD64, INTEL64,
x86-64 64-bit ABI. The default on a 32-bit host is 32-bit ABI. The default on a 64-bit host is 64-bit ABI if the target
platform specified is 64-bit, otherwise the default is 32-bit.
-
-
-
-
-
-
-
-
-
- -march=znver3
- COPTIMIZE, FOPTIMIZE
-
Specify that Clang should generate code for a specific processor family member and later. For example, if you specify
-march=znver1, the compiler is allowed to generate instructions that are valid on AMD Zen processors, but
which may not exist on earlier products.
-
-
- -ffast-math
- COPTIMIZE, FOPTIMIZE
-
Enables a range of optimizations that provide faster, though sometimes less precise, mathematical operations that may
not conform to the IEEE-754 specifications. When this option is specified, the __STDC_IEC_559__ macro is
ignored even if set by the system headers.
-
-
- -fstruct-layout=5
- COPTIMIZE
-
Analyzes the whole program to determine if the structures in the code can be peeled and if pointer or integer fields in
the structure can be compressed. If feasible, this optimization transforms the code to enable these improvements. This
transformation is likely to improve cache utilization and memory bandwidth. This, in turn, is expected to improve the
scalability of programs executed on multiple cores.
This is effective only under -flto as whole program analysis is required to perform this optimization. You can choose
different levels of aggressiveness with which this optimization can be applied to your application with 1 being the least
aggressive and 7 being the most aggressive level.
Possible values:
- fstruct-layout=1: enables structure peeling.
- fstruct-layout=2: enables structure peeling and selectively compresses self-referential pointers in these
structures to 32-bit pointers wherever safe.
- fstruct-layout=3: enables structure peeling and selectively compresses self-referential pointers in these
structures to 16-bit pointers wherever safe.
- fstruct-layout=4: enables structure peeling, pointer compression as in level 2 and further enables
compression of structure fields which are of integer type. This is performed under a strict safety check.
- fstruct-layout=5: enables structure peeling, pointer compression as in level 3 and further enables compression
of structure fields which are of integer type. This is performed under a strict safety check.
- fstruct-layout=6: enables structure peeling, pointer compression as in level 2 and further enables compression
of structure fields which are of type 64-bit 'signed int' or 'unsigned Int'. The user needs to ensure that the values
assigned to 64-bit 'signed int' fields are in range -(2^31 - 1) to +(2^31 - 1) and 64-bit 'unsigned int' fields are in
range 0 to +(2^31 - 1), otherwise, incorrect results may be obtained. This compression is performed without considering
any safety analysis and so the user needs to ensure the safety based on the program compiled.
- fstruct-layout=7: enables structure peeling, pointer compression as in level 3 and further enables compression
of structure fields which are of type 64-bit 'signed int' or 'unsigned Int'. The user needs to ensure that the values
assigned to 64-bit 'signed int' fields are in range -(2^31 - 1) to +(2^31 - 1) and 64-bit 'unsigned int' field are in
range 0 to +(2^31 - 1) , otherwise, incorrect results may be obtained. This compression is performed without considering
any safety analysis and so the user needs to ensure the safety based on the program compiled.
Note:
fstruct-layout=4 and fstruct-layout=5 are derived from fstruct-layout=2 and fstruct-layout=3 respectively with the added
feature of safe compression of integer fields in structures. Going from fstruct-layout=4 to fstruct-layout=5 may result
in higher performance if the pointer values are such that the pointers can be compressed to 16-bits.
fstruct-layout=6 and fstruct-layout=7 are derived from fstruct-layout=2 and fstruct-layout=3 respectively with the added
feature of compression of integer fields in structures. These are similar to fstruct-layout=4 and fstruct-layout=5, but
here, the integer fields of the structures are always compressed from 64-bits to 32-bits without any safety guarantee.
-
-
-
-
-
-
-
-
-
-
-
- -O3
- FOPTIMIZE
-
Like -O2, except that it enables optimizations that take longer to perform or that may generate larger code (in
an attempt to make the program run faster).
If multiple "O" options are used, with or without level numbers, the last such option is the one that is effective.
- Includes:
-
- -Mrecursive
- FOPTIMIZE
-
Allocate local variables on the stack, thus allowing recursion.
SAVEd, data-initialized, or namelist members are always allocated
statically, regardless of the setting of this switch.
-
-
-
-
-
-
-
-
-
-
-
-
- -m64
- CC, FC, LD
-
Generate code for a 64-bit environment. The 64-bit environment sets int to 32 bits and long and
pointer to 64 bits and generates code for AMD's x86-64 architecture. The compiler generates AMD64, INTEL64,
x86-64 64-bit ABI. The default on a 32-bit host is 32-bit ABI. The default on a 64-bit host is 64-bit ABI if the target
platform specified is 64-bit, otherwise the default is 32-bit.
-
-
-
-
-
-
-
-
-
- -march=znver3
- COPTIMIZE, FOPTIMIZE
-
Specify that Clang should generate code for a specific processor family member and later. For example, if you specify
-march=znver1, the compiler is allowed to generate instructions that are valid on AMD Zen processors, but
which may not exist on earlier products.
-
-
- -ffast-math
- COPTIMIZE, FOPTIMIZE
-
Enables a range of optimizations that provide faster, though sometimes less precise, mathematical operations that may
not conform to the IEEE-754 specifications. When this option is specified, the __STDC_IEC_559__ macro is
ignored even if set by the system headers.
-
-
- -fstruct-layout=5
- COPTIMIZE
-
Analyzes the whole program to determine if the structures in the code can be peeled and if pointer or integer fields in
the structure can be compressed. If feasible, this optimization transforms the code to enable these improvements. This
transformation is likely to improve cache utilization and memory bandwidth. This, in turn, is expected to improve the
scalability of programs executed on multiple cores.
This is effective only under -flto as whole program analysis is required to perform this optimization. You can choose
different levels of aggressiveness with which this optimization can be applied to your application with 1 being the least
aggressive and 7 being the most aggressive level.
Possible values:
- fstruct-layout=1: enables structure peeling.
- fstruct-layout=2: enables structure peeling and selectively compresses self-referential pointers in these
structures to 32-bit pointers wherever safe.
- fstruct-layout=3: enables structure peeling and selectively compresses self-referential pointers in these
structures to 16-bit pointers wherever safe.
- fstruct-layout=4: enables structure peeling, pointer compression as in level 2 and further enables
compression of structure fields which are of integer type. This is performed under a strict safety check.
- fstruct-layout=5: enables structure peeling, pointer compression as in level 3 and further enables compression
of structure fields which are of integer type. This is performed under a strict safety check.
- fstruct-layout=6: enables structure peeling, pointer compression as in level 2 and further enables compression
of structure fields which are of type 64-bit 'signed int' or 'unsigned Int'. The user needs to ensure that the values
assigned to 64-bit 'signed int' fields are in range -(2^31 - 1) to +(2^31 - 1) and 64-bit 'unsigned int' fields are in
range 0 to +(2^31 - 1), otherwise, incorrect results may be obtained. This compression is performed without considering
any safety analysis and so the user needs to ensure the safety based on the program compiled.
- fstruct-layout=7: enables structure peeling, pointer compression as in level 3 and further enables compression
of structure fields which are of type 64-bit 'signed int' or 'unsigned Int'. The user needs to ensure that the values
assigned to 64-bit 'signed int' fields are in range -(2^31 - 1) to +(2^31 - 1) and 64-bit 'unsigned int' field are in
range 0 to +(2^31 - 1) , otherwise, incorrect results may be obtained. This compression is performed without considering
any safety analysis and so the user needs to ensure the safety based on the program compiled.
Note:
fstruct-layout=4 and fstruct-layout=5 are derived from fstruct-layout=2 and fstruct-layout=3 respectively with the added
feature of safe compression of integer fields in structures. Going from fstruct-layout=4 to fstruct-layout=5 may result
in higher performance if the pointer values are such that the pointers can be compressed to 16-bits.
fstruct-layout=6 and fstruct-layout=7 are derived from fstruct-layout=2 and fstruct-layout=3 respectively with the added
feature of compression of integer fields in structures. These are similar to fstruct-layout=4 and fstruct-layout=5, but
here, the integer fields of the structures are always compressed from 64-bits to 32-bits without any safety guarantee.
-
-
-
-
-
-
-
-
-
-
- -Mrecursive
- FOPTIMIZE
-
Allocate local variables on the stack, thus allowing recursion.
SAVEd, data-initialized, or namelist members are always allocated
statically, regardless of the setting of this switch.
-
-
-
-
-
-
-
-
- -m64
- CC, CXX, FC, LD
-
Generate code for a 64-bit environment. The 64-bit environment sets int to 32 bits and long and
pointer to 64 bits and generates code for AMD's x86-64 architecture. The compiler generates AMD64, INTEL64,
x86-64 64-bit ABI. The default on a 32-bit host is 32-bit ABI. The default on a 64-bit host is 64-bit ABI if the target
platform specified is 64-bit, otherwise the default is 32-bit.
-
-
-
-
-
-
-
-
-
-
- -march=znver3
- COPTIMIZE, CXXOPTIMIZE, FOPTIMIZE
-
Specify that Clang should generate code for a specific processor family member and later. For example, if you specify
-march=znver1, the compiler is allowed to generate instructions that are valid on AMD Zen processors, but
which may not exist on earlier products.
-
-
- -ffast-math
- COPTIMIZE, CXXOPTIMIZE, FOPTIMIZE
-
Enables a range of optimizations that provide faster, though sometimes less precise, mathematical operations that may
not conform to the IEEE-754 specifications. When this option is specified, the __STDC_IEC_559__ macro is
ignored even if set by the system headers.
-
-
- -fstruct-layout=5
- COPTIMIZE
-
Analyzes the whole program to determine if the structures in the code can be peeled and if pointer or integer fields in
the structure can be compressed. If feasible, this optimization transforms the code to enable these improvements. This
transformation is likely to improve cache utilization and memory bandwidth. This, in turn, is expected to improve the
scalability of programs executed on multiple cores.
This is effective only under -flto as whole program analysis is required to perform this optimization. You can choose
different levels of aggressiveness with which this optimization can be applied to your application with 1 being the least
aggressive and 7 being the most aggressive level.
Possible values:
- fstruct-layout=1: enables structure peeling.
- fstruct-layout=2: enables structure peeling and selectively compresses self-referential pointers in these
structures to 32-bit pointers wherever safe.
- fstruct-layout=3: enables structure peeling and selectively compresses self-referential pointers in these
structures to 16-bit pointers wherever safe.
- fstruct-layout=4: enables structure peeling, pointer compression as in level 2 and further enables
compression of structure fields which are of integer type. This is performed under a strict safety check.
- fstruct-layout=5: enables structure peeling, pointer compression as in level 3 and further enables compression
of structure fields which are of integer type. This is performed under a strict safety check.
- fstruct-layout=6: enables structure peeling, pointer compression as in level 2 and further enables compression
of structure fields which are of type 64-bit 'signed int' or 'unsigned Int'. The user needs to ensure that the values
assigned to 64-bit 'signed int' fields are in range -(2^31 - 1) to +(2^31 - 1) and 64-bit 'unsigned int' fields are in
range 0 to +(2^31 - 1), otherwise, incorrect results may be obtained. This compression is performed without considering
any safety analysis and so the user needs to ensure the safety based on the program compiled.
- fstruct-layout=7: enables structure peeling, pointer compression as in level 3 and further enables compression
of structure fields which are of type 64-bit 'signed int' or 'unsigned Int'. The user needs to ensure that the values
assigned to 64-bit 'signed int' fields are in range -(2^31 - 1) to +(2^31 - 1) and 64-bit 'unsigned int' field are in
range 0 to +(2^31 - 1) , otherwise, incorrect results may be obtained. This compression is performed without considering
any safety analysis and so the user needs to ensure the safety based on the program compiled.
Note:
fstruct-layout=4 and fstruct-layout=5 are derived from fstruct-layout=2 and fstruct-layout=3 respectively with the added
feature of safe compression of integer fields in structures. Going from fstruct-layout=4 to fstruct-layout=5 may result
in higher performance if the pointer values are such that the pointers can be compressed to 16-bits.
fstruct-layout=6 and fstruct-layout=7 are derived from fstruct-layout=2 and fstruct-layout=3 respectively with the added
feature of compression of integer fields in structures. These are similar to fstruct-layout=4 and fstruct-layout=5, but
here, the integer fields of the structures are always compressed from 64-bits to 32-bits without any safety guarantee.
-
-
-
-
-
-
-
-
-
-
-
-
-
- -mllvm -aggressive-loop-unswitch
- CXXOPTIMIZE
-
This option enables aggressive loop unswitching heuristic (including -enable-partial-unswitch)
based on the usage of the branch conditional values. Loop unswitching leads to code-bloat. Code-bloat can be
minimized if the hoisted condition is executed more often. This heuristic prioritizes the conditions based
on the number of times they are used within the loop. The heuristic can be controlled with the following options:
- -unswitch-identical-branches-min-count=<n>
Enables unswitching of a loop with respect to a branch conditional value (B), where B appears in at least
<n> compares in the loop. This option is enabled with -aggressive-loop-unswitch. Default value is 3.
Usage: -mllvm -aggressive-loop-unswitch -mllvm -unswitch-identical-branches-min-count=<n>
where n is a positive integer and lower value of <n> facilitates more unswitching
- -unswitch-identical-branches-max-count=<n>
Enables unswitching of a loop with respect to a branch conditional value (B), where B appears in at most
<n> compares in the loop. This option is enabled with -aggressive-loop-unswitch. Default value is 6.
Usage: -mllvm -aggressive-loop-unswitch -mllvm -unswitch-identical-branches-max-count=<n>
where n is a positive integer and higher value of <n> facilitates more unswitching
Note: These options may facilitate more unswitching in some of the workloads. Since loop-unswitching inherently leads
to code bloat, facilitating more unswitching may significantly increase the code size and hence may also lead to longer
compilation times.
- Includes:
-
- -Mrecursive
- FOPTIMIZE
-
Allocate local variables on the stack, thus allowing recursion.
SAVEd, data-initialized, or namelist members are always allocated
statically, regardless of the setting of this switch.
-
-
-
-
-
-
-
Implicitly Included Flags
This section contains descriptions of flags that were included implicitly
by other flags, but which do not have a permanent home at SPEC.
-
- -O2
-
Moderate level of optimization which enables most optimizations. This is the default when no "-O" option is
specified, or if no value is specified (i.e. "-O").
If multiple "O" options are used, with or without level numbers, the last such option is the one that is effective.
- Includes:
-
- -O1
-
Somewhere between -O0 and -O2.
If multiple "O" options are used, with or without level numbers, the last such option is the one that is effective.
-
-
- -O3
-
Like -O2, except that it enables optimizations that take longer to perform or that may generate larger code (in
an attempt to make the program run faster).
If multiple "O" options are used, with or without level numbers, the last such option is the one that is effective.
- Includes:
Using numactl to bind processes and memory to cores
For multi-copy runs or single copy runs on systems with multiple sockets, it is advantageous to bind a process to a
particular core. Otherwise, the OS may arbitrarily move your process from one core to another. This can affect
performance. To help, SPEC allows the use of a "submit" command where users can specify a utility to use to bind
processes. We have found the utility 'numactl' to be the best choice.
numactl runs processes with a specific NUMA scheduling or memory placement policy. The policy is set for a
command and inherited by all of its children. The numactl flag "--physcpubind" specifies
which core(s) to bind the process. "-l" instructs numactl to keep a process's memory on the
local node while "-m" specifies which node(s) to place a process's memory. For full details on using
numactl, please refer to your Linux documentation, 'man numactl'
Note that some older versions of numactl incorrectly interpret application arguments as its own. For
example, with the command "numactl --physcpubind=0 -l a.out -m a", numactl will interpret
a.out's "-m" option as its own "-m" option. To work around this problem, we put
the command to be run in a shell script and then run the shell script using numactl. For example:
"echo 'a.out -m a' > run.sh ; numactl --physcpubind=0 bash run.sh"
Transparent Huge Pages (THP)
THP is an abstraction layer that automates most aspects of creating, managing, and using huge pages. THP is designed
to hide much of the complexity in using huge pages from system administrators and developers, as normal huge pages
must be assigned at boot time, can be difficult to manage manually, and often require significant changes to code in
order to be used effectively. Most recent Linux OS releases have THP enabled by default.
ulimit -s <n>
Sets the stack size to n kbytes, or unlimited to allow the stack size to grow without limit.
ulimit -l <n>
Sets the maximum size of memory that may be locked into physical memory.
powersave -f (on SuSE)
Makes the powersave daemon set the CPUs to the highest supported frequency.
/etc/init.d/cpuspeed stop (on Red Hat)
Disables the cpu frequency scaling program in order to set the CPUs to the highest supported frequency.
LD_LIBRARY_PATH
An environment variable that indicates the location in the filesystem of bundled libraries to use when running the
benchmark binaries.
kernel/randomize_va_space
This option can be used to select the type of process address space randomization that is used in the system, for
architectures that support this feature.
- 0 - Turn the process address space randomization off. This is the default for architectures that do not support
this feature anyway, and kernels that are booted with the "
norandmaps" parameter.
- 1 - Make the addresses of mmap base, stack and VDSO page randomized. This, among other things, implies that
shared libraries will be loaded to random addresses. Also for PIE-linked binaries, the location of code start is
randomized. This is the default if the
CONFIG_COMPAT_BRK option is enabled.
- 2 - Additionally enable heap randomization. This is the default if
CONFIG_COMPAT_BRK is
disabled.
MALLOC_CONF
An environment variable set to tune the jemalloc allocation strategy during the execution of the binaries. This
environment variable setting is not needed when building the binaries on the system under test.
PGHPF_ZMEM
An environment variable used to initialize the allocated memory. Setting PGHPF_ZMEM to "Yes" has the effect of
initializing all allocated memory to zero.
GOMP_CPU_AFFINITY
This environment variable is used to set the thread affinity for threads spawned by OpenMP.
OMP_DYNAMIC
This environment variable is defined as part of the OpenMP standard.
Setting it to "false" prevents the OpenMP runtime from dynamically adjusting the number of threads to use for parallel
execution.
For more information, see chapter 4 ("Environment Variables") in the
OpenMP 4.5 Specification.
OMP_SCHEDULE
This environment variable is defined as part of the OpenMP standard.
Setting it to "static" causes loop iterations to be assigned to threads in round-robin fashion in the order of the thread
number.
For more information, see chapter 4 ("Environment Variables") in the
OpenMP 4.5 Specification.
OMP_STACKSIZE
This environment variable is defined as part of the OpenMP standard and controls the size of the stack for threads created
by OpenMP.
For more information, see chapter 4 ("Environment Variables") in the
OpenMP 4.5 Specification.
OMP_THREAD_LIMIT
This environment variable is defined as part of the OpenMP standard and limits the maximum number of OpenMP threads that
can be created.
For more information, see chapter 4 ("Environment Variables") in the
OpenMP 4.5 Specification.
- kernel.randomize_va_space (ASLR)
-
This setting can be used to select the type of process address space
randomization. Defaults differ based on whether the architecture supports
ASLR, whether the kernel was built with the CONFIG_COMPAT_BRK
option or not, or the kernel boot options used.
Possible settings:
- 0: Turn process address space randomization off.
- 1: Randomize addresses of mmap base, stack, and VDSO pages.
- 2: Additionally randomize the heap. (This is probably the default.)
Disabling ASLR can make process execution more deterministic and runtimes more consistent.
For more information see the randomize_va_space entry in the
Linux sysctl
documentation.
Transparent Hugepages (THP)-
THP is an abstraction layer that automates most aspects of creating, managing,
and using huge pages. It is designed to hide much of the complexity in using
huge pages from system administrators and developers. Huge pages
increase the memory page size from 4 kilobytes to 2 megabytes. This provides
significant performance advantages on systems with highly contended resources
and large memory workloads. If memory utilization is too high or memory is badly
fragmented which prevents hugepages being allocated, the kernel will assign
smaller 4k pages instead. Most recent Linux OS releases have THP enabled by default.
THP usage is controlled by the sysfs setting /sys/kernel/mm/transparent_hugepage/enabled.
Possible values:
- never: entirely disable THP usage.
- madvise: enable THP usage only inside regions marked MADV_HUGEPAGE using madvise(3).
- always: enable THP usage system-wide. This is the default.
THP creation is controlled by the sysfs setting /sys/kernel/mm/transparent_hugepage/defrag.
Possible values:
- never: if no THP are available to satisfy a request, do not attempt to make any.
- defer: an allocation requesting THP when none are available get normal pages while requesting THP creation in the background.
- defer+madvise: acts like "always", but only for allocations in regions marked MADV_HUGEPAGE using madvise(3); for all other regions it's like "defer".
- madvise: acts like "always", but only for allocations in regions marked MADV_HUGEPAGE using madvise(3). This is the default.
- always: an allocation requesting THP when none are available will stall until some are made.
An application that "always" requests THP often can benefit from waiting for an allocation until those huge pages can be assembled.
For more information see the Linux transparent hugepage documentation.
C States:
C States allow the processor to enter lower power states when idle. When set to Enabled (OS controlled)
or when set to Autonomous (if Hardware controlled is supported), the processor can operate in all
available Power States to save power, but my increase memory latency and frequency jitter.
L3 cache as NUMA Domain:
This field specifies that each CCX within the processor will be declared as a NUMA Domain.
Dram Refresh Delay:
By enabling CPU memory controller to delay running the REFRESH commands, you can improve the performance for some workloads. By minimizing the delay time,
it is ensured that the memory controller runs the REFRESH command at regular intervals. For Intel-based servers, this setting only affects systems configured
with DIMMs which use 8Gb density DRAMs.
L1 Stream HW prefetcher, L2 Stream HW prefetcher:
Most workloads will benefit from the L1 and L2 Stream Hardware prefetchers gathering data and keeping the core pipeline busy. There are however some workloads that are very random in nature and will actually obtain better overall performance by disabling one or both of the prefetchers.
UPI Prefetch:
Enables you to get the memory read started early on DDR bus. The Ultra Path Interconnect (UPI) Rx path will spawn the speculative memory read to Integrated Memory Controller (iMC) directly.
Dynamic Link Width Management (DLWM):
DLWM reduces the XGMI link width between sockets from x16 to x8 (default), when no traffic is detected on the link. This feature is optimized to trade power between core and high IO/memory bandwidth workloads.
Forced = Force link width to x16, x8, or x2.
LLC Prefetch:
This option configures the processor last level cache (LLC) prefetch feature as a result of the non-inclusive cache architecture. The LLC prefetcher exists on top of other prefetchers that can prefetch data into the core data cache unit (DCU) and mid-level cache (MLC). In some cases, setting this option to disabled can improve performance. Typically, setting this option to enable provides better performance. Disabled: Disables the LLC prefetcher. Enabled: Gives the core prefetcher the ability to prefetch data directly to the LLC.
Dead Line LLC Alloc:
In the Skylake cache scheme, mid-level cache (MLC) evictions are filled into the last level cache (LLC). If a line is evicted from the MLC to the LLC, the Skylake core can flag the evicted MLC lines as "dead". This means that the lines are not likely to be read again. This option allows dead lines to be dropped and never fill the LLC if the option is disabled. Disabled: Disabling this option can save space in the LLC by never filling dead lines into the LLC. Enabled: Opportunistically fill dead lines in LLC, if space is available.
Directory AtoS:
AtoS optimization reduces remote read latencies for repeat read accesses without intervening writes.
Algorithm performance Boost Disable (ApbDis):
When enabled a specific hard-fused Data Fabric (SOC) p-state is forced for optimizing workloads sensitive to latency or throughput. When disabled P-states will be automatically managed by the Application Power Management, allowing the processor to provide maximum performance while remaining within a specified power-delivery and thermal envelope.
Fan Speed:
Selecting this option allows additional cooling to the server. In case hardware is added (example, new PCIe cards), it may require additional cooling. A fan speed offset causes fan speeds to increase (by the offset % value) over baseline fan speeds calculated by the Thermal Control algorithm. Maximum — Drives fan speeds to full speed.
Determinism Slider:
It controls whether BIOS will enable determinism to control performance.
Performance: BIOS will enable 100% deterministic performance control.
Power: BIOS will not enable deterministic performance control.
CPU Power Management set to Maximum Performance:
Allows selection of CPU power management methodology. Maximum Performance is typically selected for performance-centric workloads where it is acceptable to consume additional power to achieve the highest possible performance for the computing environment. This mode drives processor frequency to the maximum across all cores (although idled cores can still be frequency reduced by C-state enforcement through BIOS or OS mechanisms if enabled). This mode also offers the lowest latency of the CPU Power Management Mode options, so is always preferred for latency-sensitive environments. OS DBPM is another performance-per-watt option that relies on the operating system to dynamically control individual cores in order to save power.
Memory Frequency set to Maximum Performance:
Governs the BIOS memory frequency. The variables that govern maximum memory frequency include the maximum rated frequency of the DIMMs, the DIMMs per channel population, the processor choice, and this BIOS option. Additional power savings can be achieved by reducing the memory frequency, at the expense of reduced performance. Read-only unless System Profile is set to Custom.
Efficiency Optimized Mode Disabled:
This field enables/disabled Efficiency Optimized Mode. Efficiency Optimized Mode maximizes Performance-per-Watt by opportunistically reducing frequency/power.
NUMA Nodes Per Socket:
NUMA nodes per socket (NPS) field allows you to configure the memory NUMA domains per socket. The configuration can consist of one whole domain (NPS1), two domains (NPS2), or four domains (NPS4). In the case of a two-socket platform, an additional NPS profile is available to have whole system memory to be mapped as single NUMA domain (NPS0).
CCX as NUMA Domain:
In addition to selecting the number of NUMA domains via NPS option, the processor allows for making memory per CCX as NUMA domain. In the processor each CCD has a maximum of two CCXs with each CCX having a shared last-level cache (LLC, or L3 cache) for all cores. The CCX as NUMA domain option allows for each LLC to be configured as a NUMA domain so that for certain workloads pinning execution to a single NUMA domain can be done.
Adaptive Double DRAM Device Correction (ADDDC):
When Adaptive Double DRAM Device Correction (ADDDC) is enabled, failing DRAM’s are dynamically mapped out. When set to enabled, it can have some impact to system performance under certain workloads. This feature is applicable for x4 DIMMs only.
DCU Streamer Prefetcher:
Enables or disables Data Cache Unit (DCU) Streamer Prefetcher. This setting can affect performance, depending on the application running on the server. DCU streamer prefetchers detect multiple reads to a single cache line in a certain period of time and choose to load the following cache line to the L1 data caches. Recommended for High Performance Computing applications.
DCU IP Prefetcher:
Enables or disables Data Cache Unit (DCU) IP Prefetcher. DCU IP Prefetcher looks for sequential load history to determine whether to prefetch the data to the L1 caches.
Memory Frequency:
Governs the BIOS memory frequency. The variables that govern maximum memory frequency include the maximum rated frequency of the DIMMs, the DIMMs per channel population, the processor choice, and this BIOS option. Additional power savings can be achieved by reducing the memory frequency, at the expense of reduced performance.
Turbo Boost:
Governs the Boost Technology. This feature allows the processor cores to be automatically clocked up in frequency beyond the advertised processor speed. The amount of increased frequency (or 'turbo upside') one can expect from an EPYC processor depends on the fewer cores being exercised with work the higher the potential turbo upside. The potential drawback for Boost are mainly centered on increased power consumption and possible frequency jitter that can affect a small minority of latency-sensitive environments.
C1E:
When set to Enabled, the processor is allowed to switch to minimum performance state when idle.
CPU Interconnect Bus Link Power Management:
When Enabled, CPU interconnect bus link power management can reduce overall system power a
bit while slightly reducing system performance.
CPU Performance:
Maximum Performance is typically selected for performance-centric workloads where it
is acceptable to consume additional power to achieve the highest possible performance
for the computing environment. This mode drives processor frequency to the maximum
across all cores (although idled cores can still be frequency reduced by C-state
enforcement through BIOS or OS mechanisms if enabled). This mode also offers the
lowest latency of the CPU Power Management Mode options, so is always preferred.
Energy Efficient Policy:
The CPU uses the setting to manipulate the internal behavior of the processor and determines
whether to target higher performance or better power savings. The possible settings are: Performance, Balanced Performance, Balanced Energy, Energy Efficient.
Energy Efficient Turbo:
Permits Energy Efficient Turbo to be Enabled or Disabled.
Energy Efficient Turbo (EET) is a mode of operation where a processor's core frequency is adjusted within the turbo range based on workload.
Logical Processor:
Each processor core supports up to two logical processors. When set to Enabled, the BIOS
reports all logical processors. When set to Disabled, the BIOS only reports one
logical processor per core. Generally, higher processor count results in increased
performance for most multi-threaded workloads and the recommendation is to keep this enabled.
However, there are some floating point/scientific workloads, including HPC workloads, where
disabling this feature may result in higher performance.
Memory Patrol Scrub:
Patrol Scrubbing searches the memory for errors and repairs correctable errors to prevent
the accumulation of memory errors. When set to Disabled, no patrol scrubbing will occur.
When set to Standard Mode, the entire memory array will be scrubbed once in a 24 hour period.
When set to Extended Mode, the entire memory array will be scrubbed more frequently to further
increase system reliability.
Memory Refresh Rate:
The memory controller will periodically refresh the data in memory. The frequency at which memory is normally refreshed is referred to as 1X refresh rate. When memory modules are operating at a higher than normal temperature or to further increase system reliability, the refresh rate can be set to 2X, but may have a negative impact on memory subsystem performance under some circumstances.
PCI ASPM L1 Link Power Management:
When Enabled, PCIe Advanced State Power Management (ASPM) can reduce overall system power
a bit while slightly reducing system performance.
NOTE: Some devices may not perform properly (they may hang or cause the system to hang)
when ASPM is enabled, for this reason L1 will only be enabled for validated qualified cards.
System Profile:
When set to Custom, you can change setting of each option. Under Custom mode when C States is enabled,
Monitor/Mwait should also be Enabled.
Monitor/Mwait:
Specifies whether Monitor/Mwait instructions are enabled. Monitor/Mwait is only active when C States is set to Disabled.
Sub NUMA Cluster:
When Enabled, Sub NUMA Clustering (SNC) is a feature for breaking up the LLC into disjoint clusters based on address range,
with each cluster bound to a subset of the memory controllers in the system.
It improves average latency to the LLC.
Uncore Frequency:
Selects the Processor Uncore Frequency.
Dynamic mode allows processor to optimize power resources across the cores and uncore during runtime.
The optimization of the uncore frequency to either save power or optimize performance is influenced
by the setting of the Energy Efficient Policy.
Virtualization Technology:
When set to Enabled, the BIOS will enable processor Virtualization features and provide the virtualization
support to the Operating System (OS) through the DMAR table. In general, only virtualized environments
such as VMware(r) ESX (tm), Microsoft Hyper-V(r) , Red Hat(r) KVM, and other virtualized operating systems
will take advantage of these features. Disabling this feature is not known to significantly alter the
performance or power characteristics of the system, so leaving this option Enabled is advised for most cases.
nohz_full:
This kernel option sets adaptive tick mode (NOHZ_FULL) to specified processors. Since the number of interrupts is reduced to ones per second, latency-sensitive applications can take advantage of it.
Memory Interleaving:
When Enabled, memory interleaving is supported if a symmetric memory configuration is installed. When set to Disabled, the system supports Non-Uniform Memory Access (NUMA) (asymmetric) memory configurations. Channel interleaving is available with all configurations and is the intra-die memory interleave option. With channel interleaving the memory behind each UMC will be interleaved and seen as 1 NUMA domain per die.
For questions about the meanings of these flags, please contact the tester.
For other inquiries, please contact info@spec.org
Copyright 2017-2021 Standard Performance Evaluation Corporation
Tested with SPEC CPU2017 v1.1.5.
Report generated on 2021-03-16 18:36:16 by SPEC CPU2017 flags formatter v5178.
![[benchmark]](https://www.spec.org/auto/cpu2017/images/benchmark.png)