[libc-commits] [libc] [libc] Make fenv utility functions constexpr. (PR #150447)

[via libc-commits]

https://github.com/lntue created https://github.com/llvm/llvm-project/pull/150447

None

>From 318c2674d24093671f6c63f1619c73e68667456b Mon Sep 17 00:00:00 2001
From: Tue Ly <lntue.h at gmail.com>
Date: Thu, 24 Jul 2025 16:00:22 +0000
Subject: [PATCH] [libc] Make fenv utility functions constexpr.

---
 libc/src/__support/FPUtil/CMakeLists.txt |  1 +
 libc/src/__support/FPUtil/FEnvImpl.h     | 51 ++++++++++++++++--------
 2 files changed, 36 insertions(+), 16 deletions(-)

diff --git a/libc/src/__support/FPUtil/CMakeLists.txt b/libc/src/__support/FPUtil/CMakeLists.txt
index 94f8b95542470..6e447fcd47368 100644
--- a/libc/src/__support/FPUtil/CMakeLists.txt
+++ b/libc/src/__support/FPUtil/CMakeLists.txt
@@ -7,6 +7,7 @@ add_header_library(
     libc.hdr.fenv_macros
     libc.hdr.math_macros
     libc.hdr.stdint_proxy
+    libc.src.__support.CPP.type_traits
     libc.src.__support.macros.attributes
     libc.src.errno.errno
 )
diff --git a/libc/src/__support/FPUtil/FEnvImpl.h b/libc/src/__support/FPUtil/FEnvImpl.h
index 76910880eb810..7bd56434e58fe 100644
--- a/libc/src/__support/FPUtil/FEnvImpl.h
+++ b/libc/src/__support/FPUtil/FEnvImpl.h
@@ -12,6 +12,7 @@
 #include "hdr/fenv_macros.h"
 #include "hdr/math_macros.h"
 #include "hdr/types/fenv_t.h"
+#include "src/__support/CPP/type_traits.h"
 #include "src/__support/libc_errno.h"
 #include "src/__support/macros/attributes.h" // LIBC_INLINE
 #include "src/__support/macros/config.h"
@@ -72,40 +73,58 @@ LIBC_INLINE int set_env(const fenv_t *) { return 0; }
 namespace LIBC_NAMESPACE_DECL {
 namespace fputil {
 
-LIBC_INLINE static int clear_except_if_required([[maybe_unused]] int excepts) {
+LIBC_INLINE static constexpr int
+clear_except_if_required([[maybe_unused]] int excepts) {
+  if (cpp::is_constant_evaluated()) {
+    return 0;
+  } else {
 #ifndef LIBC_MATH_HAS_NO_EXCEPT
-  if (math_errhandling & MATH_ERREXCEPT)
-    return clear_except(excepts);
+    if (math_errhandling & MATH_ERREXCEPT)
+      return clear_except(excepts);
 #endif // LIBC_MATH_HAS_NO_EXCEPT
-  return 0;
+    return 0;
+  }
 }
 
-LIBC_INLINE static int set_except_if_required([[maybe_unused]] int excepts) {
+LIBC_INLINE static constexpr int
+set_except_if_required([[maybe_unused]] int excepts) {
+  if (cpp::is_constant_evaluated()) {
+    return 0;
+  } else {
 #ifndef LIBC_MATH_HAS_NO_EXCEPT
-  if (math_errhandling & MATH_ERREXCEPT)
-    return set_except(excepts);
+    if (math_errhandling & MATH_ERREXCEPT)
+      return set_except(excepts);
 #endif // LIBC_MATH_HAS_NO_EXCEPT
-  return 0;
+    return 0;
+  }
 }
 
-LIBC_INLINE static int raise_except_if_required([[maybe_unused]] int excepts) {
+LIBC_INLINE static constexpr int
+raise_except_if_required([[maybe_unused]] int excepts) {
+  if (cpp::is_constant_evaluated()) {
+    return 0;
+  } else {
 #ifndef LIBC_MATH_HAS_NO_EXCEPT
-  if (math_errhandling & MATH_ERREXCEPT)
+    if (math_errhandling & MATH_ERREXCEPT)
 #ifdef LIBC_TARGET_ARCH_IS_X86_64
-    return raise_except</*SKIP_X87_FPU*/ true>(excepts);
+      return raise_except</*SKIP_X87_FPU*/ true>(excepts);
 #else  // !LIBC_TARGET_ARCH_IS_X86
-    return raise_except(excepts);
+      return raise_except(excepts);
 #endif // LIBC_TARGET_ARCH_IS_X86
 
 #endif // LIBC_MATH_HAS_NO_EXCEPT
-  return 0;
+    return 0;
+  }
 }
 
-LIBC_INLINE static void set_errno_if_required([[maybe_unused]] int err) {
+LIBC_INLINE static constexpr void
+set_errno_if_required([[maybe_unused]] int err) {
+  if (!cpp::is_constant_evaluated()) {
 #ifndef LIBC_MATH_HAS_NO_ERRNO
-  if (math_errhandling & MATH_ERRNO)
-    libc_errno = err;
+    if (math_errhandling & MATH_ERRNO)
+      libc_errno = err;
 #endif // LIBC_MATH_HAS_NO_ERRNO
+  }
 }
 
 } // namespace fputil