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[libc] Simplify fma handling for riscv #149673

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Merged
mikhailramalho merged 2 commits into from
Jul 19, 2025
Merged

[libc] Simplify fma handling for riscv #149673

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e8a526a
[libc] Simplify fma handling for riscv
mikhailramalho Jul 19, 2025
aa6b450
Fix alignment
mikhailramalho Jul 19, 2025
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[libc] Simplify fma handling for riscv 
This PR simplifies how we enable the different fma configs for riscv:

1. Removes __LIBC_RISCV_USE_FMA define
2. Checks if __riscv_flen is defined to set LIBC_TARGET_CPU_HAS_FMA

As a bonus we enable *FMA_OPT tests for rv32, so any rv32 hardware that
doesn't implement the f/d extensions are also tested.
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@mikhailramalho
mikhailramalho committed Jul 19, 2025
commit e8a526a7a3a6748c0167a98f44cb54740b9ac68d
2 changes: 2 additions & 0 deletions libc/cmake/modules/LLVMLibCArchitectures.cmake
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Expand Up @@ -153,9 +153,11 @@ elseif(LIBC_TARGET_ARCHITECTURE STREQUAL "x86_64")
elseif(LIBC_TARGET_ARCHITECTURE STREQUAL "i386")
set(LIBC_TARGET_ARCHITECTURE_IS_X86 TRUE)
elseif(LIBC_TARGET_ARCHITECTURE STREQUAL "riscv64")
set(LIBC_TARGET_ARCHITECTURE_IS_ANY_RISCV TRUE)
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set(LIBC_TARGET_ARCHITECTURE_IS_RISCV64 TRUE)
set(LIBC_TARGET_ARCHITECTURE "riscv")
elseif(LIBC_TARGET_ARCHITECTURE STREQUAL "riscv32")
set(LIBC_TARGET_ARCHITECTURE_IS_ANY_RISCV TRUE)
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set(LIBC_TARGET_ARCHITECTURE_IS_RISCV32 TRUE)
set(LIBC_TARGET_ARCHITECTURE "riscv")
elseif(LIBC_TARGET_ARCHITECTURE STREQUAL "amdgpu")
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4 changes: 1 addition & 3 deletions libc/cmake/modules/LLVMLibCCompileOptionRules.cmake
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Expand Up @@ -13,7 +13,7 @@ endif()
function(_get_compile_options_from_flags output_var)
set(compile_options "")

if(LIBC_TARGET_ARCHITECTURE_IS_RISCV64 OR(LIBC_CPU_FEATURES MATCHES "FMA"))
if(LIBC_CPU_FEATURES MATCHES "FMA")
check_flag(ADD_FMA_FLAG ${FMA_OPT_FLAG} ${ARGN})
endif()
check_flag(ADD_ROUND_OPT_FLAG ${ROUND_OPT_FLAG} ${ARGN})
Expand All @@ -25,8 +25,6 @@ function(_get_compile_options_from_flags output_var)
if(LIBC_TARGET_ARCHITECTURE_IS_X86_64)
list(APPEND compile_options "-mavx2")
list(APPEND compile_options "-mfma")
elseif(LIBC_TARGET_ARCHITECTURE_IS_RISCV64)
list(APPEND compile_options "-D__LIBC_RISCV_USE_FMA")
endif()
# For clang, we will build the math functions with `-fno-math-errno` so that
# __builtin_fma* will generate the fused-mutliply-add instructions. We
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2 changes: 1 addition & 1 deletion libc/cmake/modules/LLVMLibCFlagRules.cmake
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Expand Up @@ -270,7 +270,7 @@ set(MISC_MATH_BASIC_OPS_OPT_FLAG "MISC_MATH_BASIC_OPS_OPT")
# Skip FMA_OPT flag for targets that don't support fma.
if(NOT DEFINED SKIP_FLAG_EXPANSION_FMA_OPT)
if(NOT((LIBC_TARGET_ARCHITECTURE_IS_X86_64 AND (LIBC_CPU_FEATURES MATCHES "FMA")) OR
LIBC_TARGET_ARCHITECTURE_IS_RISCV64))
LIBC_TARGET_ARCHITECTURE_IS_ANY_RISCV))
set(SKIP_FLAG_EXPANSION_FMA_OPT TRUE)
endif()
endif()
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2 changes: 1 addition & 1 deletion libc/src/__support/macros/properties/cpu_features.h
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Expand Up @@ -81,7 +81,7 @@
#endif

#if defined(__ARM_FEATURE_FMA) || (defined(__AVX2__) && defined(__FMA__)) || \
defined(__NVPTX__) || defined(__AMDGPU__) || defined(__LIBC_RISCV_USE_FMA)
defined(__NVPTX__) || defined(__AMDGPU__) || defined(__riscv_flen)
#define LIBC_TARGET_CPU_HAS_FMA
// Provide a more fine-grained control of FMA instruction for ARM targets.
#if defined(LIBC_TARGET_CPU_HAS_FPU_HALF)
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