[Driver] Default to -fno-math-errno for musl too

[alxu]

Summary

musl does not set errno in math functions: https://wiki.musl-libc.org/mathematical-library.html, https://git.musl-libc.org/cgit/musl/tree/include/math.h?id=cfdfd5ea3ce14c6abf7fb22a531f3d99518b5a1b#n26.

[alxu]

Hi, can someone take a look at this? @MaskRay, @pirama, @srhines? Thanks!

[srhines]

Verified with the docs from musl.

[MaskRay]

Looks great!

Thanks for telling me that GCC overloads -fno-math-errno to mean that malloc does not set errno (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88576). This looks really scary. Clang doesn't have the problem:)

[pirama]

@alxu Just realized you don't have commit access. Do you want one of us to merge this?

[alxu]

In D116753#3298299, @pirama wrote:

@alxu Just realized you don't have commit access. Do you want one of us to merge this?

Yes, I forgot about this patch. Thanks.

[MaskRay]

I am testing check-clang-driver and will cherry pick this into release/14.x.

Since the diff was not created with arc diff, the author name/email information isn't available, but I get the information offline.

clang/lib/Driver/ToolChains/Linux.cpp

if (RtLib == ToolChain::RLT_CompilerRT)
     return true;
   assert(RtLib == ToolChain::RLT_Libgcc && "unexpected runtime library type!");
   if (GCCInstallation.getVersion().isOlderThan(9, 3, 1))
     return false;
   return true;
 }
 
 bool Linux::IsMathErrnoDefault() const {
-  if (getTriple().isAndroid())
+  if (getTriple().isAndroid() || getTriple().isMusl())
     return false;
   return Generic_ELF::IsMathErrnoDefault();
 }
 
 SanitizerMask Linux::getSupportedSanitizers() const {
   const bool IsX86 = getTriple().getArch() == llvm::Triple::x86;
   const bool IsX86_64 = getTriple().getArch() == llvm::Triple::x86_64;
   const bool IsMIPS = getTriple().isMIPS32();

clang/test/Driver/fast-math.c

 // RUN: %clang -### -target x86_64-unknown-openbsd -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-MATH-ERRNO %s
 // RUN: %clang -### -target x86_64-unknown-dragonfly -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-MATH-ERRNO %s
 // RUN: %clang -### -target x86_64-fuchsia -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-MATH-ERRNO %s
 // RUN: %clang -### -target x86_64-linux-android -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-MATH-ERRNO %s
+// RUN: %clang -### -target x86_64-linux-musl -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-MATH-ERRNO %s
 // RUN: %clang -### -target amdgcn-amd-amdhsa -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-MATH-ERRNO %s
 // RUN: %clang -### -target amdgcn-amd-amdpal -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-MATH-ERRNO %s
 // RUN: %clang -### -target amdgcn-mesa-mesa3d -c %s 2>&1   \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-MATH-ERRNO %s
 //
 // Check that -ffast-math disables -fmath-errno, and -fno-fast-math merely