[libc-commits] [libc] [libc] Set -fno-math-errno for FMA (PR #125752)

[Petr Hosek via libc-commits]

https://github.com/petrhosek created https://github.com/llvm/llvm-project/pull/125752

We need to set -fno-math-errno so __builtin_fma* generate the fused-multiply-add instructions rather than an fma call.

>From 672cc84ffbf61dbf0ab04e65357b4e819a098d87 Mon Sep 17 00:00:00 2001
From: Petr Hosek <phosek at google.com>
Date: Tue, 4 Feb 2025 20:03:57 +0000
Subject: [PATCH] [libc] Set -fno-math-errno for FMA

We need to set -fno-math-errno so __builtin_fma* generate the
fused-multiply-add instructions rather than an fma call.
---
 libc/src/__support/FPUtil/CMakeLists.txt | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/libc/src/__support/FPUtil/CMakeLists.txt b/libc/src/__support/FPUtil/CMakeLists.txt
index 522b4afefd48d6..339bb58838564c 100644
--- a/libc/src/__support/FPUtil/CMakeLists.txt
+++ b/libc/src/__support/FPUtil/CMakeLists.txt
@@ -122,6 +122,10 @@ add_header_library(
     libc.src.__support.FPUtil.generic.fma
   FLAGS
     FMA_OPT
+  COMPILE_OPTIONS
+    # We need to set -fno-math-errno so __builtin_fma* generate
+    # the fused-mutliply-add instructions rather than an fma call.
+    -fno-math-errno
 )
 
 add_header_library(
@@ -132,6 +136,10 @@ add_header_library(
     libc.src.__support.common
   FLAGS
     FMA_OPT
+  COMPILE_OPTIONS
+    # We need to set -fno-math-errno so __builtin_fma* generate
+    # the fused-mutliply-add instructions rather than an fma call.
+    -fno-math-errno
 )
 
 add_header_library(