[clang] [clang] Make -fveclib={ArmPL, SLEEF} imply -fno-math-errno (PR #112580)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-driver

Author: Benjamin Maxwell (MacDue)

<details>
<summary>Changes</summary>

These two veclibs are only available for AArch64 targets, and as mentioned in https://discourse.llvm.org/t/rfc-should-fveclib-imply-fno-math-errno-for-all-targets/81384, we (Arm) think that `-fveclib` should imply `-fno-math-errno`. By setting `-fveclib` the user shows they intend to use the vector math functions, which implies they don't care about errno. However, currently, the vector mappings won't be used in many cases without setting `-fno-math-errno` separately.

Making this change would also help resolve some inconsistencies in how vector mappings are applied (see https://github.com/llvm/llvm-project/pull/108980#discussion_r1766555560).

Note: Both SLEEF and ArmPL state that they do not set `errno`:

- https://developer.arm.com/documentation/101004/2410/General-information/Arm-Performance-Libraries-math-functions
  *  "The vector functions in libamath which are available on Linux may not set errno nor raise exceptions"
- https://sleef.org/2-references/libm/
  *  "These functions do not set errno nor raise an exception."

---
Full diff: https://github.com/llvm/llvm-project/pull/112580.diff


3 Files Affected:

- (modified) clang/include/clang/Driver/Options.td (+2-1) 
- (modified) clang/lib/Driver/ToolChains/Clang.cpp (+8) 
- (modified) clang/test/Driver/fveclib.c (+7) 


``````````diff
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 379e75b197cf96..7965f70e290408 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -3410,7 +3410,8 @@ def fno_experimental_isel : Flag<["-"], "fno-experimental-isel">, Group<f_clang_
   Alias<fno_global_isel>;
 def fveclib : Joined<["-"], "fveclib=">, Group<f_Group>,
   Visibility<[ClangOption, CC1Option, FlangOption, FC1Option]>,
-    HelpText<"Use the given vector functions library">,
+    HelpText<"Use the given vector functions library."
+             "Note: -fveclib={ArmPL,SLEEF} implies -fno-math-errno">,
     Values<"Accelerate,libmvec,MASSV,SVML,SLEEF,Darwin_libsystem_m,ArmPL,AMDLIBM,none">,
     NormalizedValuesScope<"llvm::driver::VectorLibrary">,
     NormalizedValues<["Accelerate", "LIBMVEC", "MASSV", "SVML", "SLEEF",
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 3fc39296f44281..7e7f3770cfb62d 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -2854,6 +2854,10 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
                                        bool OFastEnabled, const ArgList &Args,
                                        ArgStringList &CmdArgs,
                                        const JobAction &JA) {
+  // List of veclibs which when used with -fveclib imply -fno-math-errno.
+  constexpr std::array VecLibImpliesNoMathErrno{llvm::StringLiteral("ArmPL"),
+                                                llvm::StringLiteral("SLEEF")};
+
   // Handle various floating point optimization flags, mapping them to the
   // appropriate LLVM code generation flags. This is complicated by several
   // "umbrella" flags, so we do this by stepping through the flags incrementally
@@ -3125,6 +3129,10 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
       TrappingMathPresent = true;
       FPExceptionBehavior = "strict";
       break;
+    case options::OPT_fveclib:
+      if (llvm::is_contained(VecLibImpliesNoMathErrno, A->getValue()))
+        MathErrno = false;
+      break;
     case options::OPT_fno_trapping_math:
       if (!TrappingMathPresent && !FPExceptionBehavior.empty() &&
           FPExceptionBehavior != "ignore")
diff --git a/clang/test/Driver/fveclib.c b/clang/test/Driver/fveclib.c
index 9b0f1ce13aa2bd..2a3133541e3b72 100644
--- a/clang/test/Driver/fveclib.c
+++ b/clang/test/Driver/fveclib.c
@@ -36,16 +36,23 @@
 /* Verify that the correct vector library is passed to LTO flags. */
 
 // RUN: %clang -### --target=x86_64-unknown-linux-gnu -fveclib=LIBMVEC -flto %s 2>&1 | FileCheck --check-prefix=CHECK-LTO-LIBMVEC %s
+// CHECK-LTO-LIBMVEC: "-fmath-errno"
 // CHECK-LTO-LIBMVEC: "-plugin-opt=-vector-library=LIBMVEC-X86"
 
 // RUN: %clang -### --target=powerpc64-unknown-linux-gnu -fveclib=MASSV -flto %s 2>&1 | FileCheck --check-prefix=CHECK-LTO-MASSV %s
+// CHECK-LTO-MASSV: "-fmath-errno"
 // CHECK-LTO-MASSV: "-plugin-opt=-vector-library=MASSV"
 
 // RUN: %clang -### --target=x86_64-unknown-linux-gnu -fveclib=SVML -flto %s 2>&1 | FileCheck --check-prefix=CHECK-LTO-SVML %s
+// CHECK-LTO-SVML: "-fmath-errno"
 // CHECK-LTO-SVML: "-plugin-opt=-vector-library=SVML"
 
 // RUN: %clang -### --target=aarch64-linux-gnu -fveclib=SLEEF -flto %s 2>&1 | FileCheck --check-prefix=CHECK-LTO-SLEEF %s
+// CHECK-LTO-SLEEF-NOT: "-fmath-errno"
 // CHECK-LTO-SLEEF: "-plugin-opt=-vector-library=sleefgnuabi"
+// CHECK-LTO-SLEEF-NOT: "-fmath-errno"
 
 // RUN: %clang -### --target=aarch64-linux-gnu -fveclib=ArmPL -flto %s 2>&1 | FileCheck --check-prefix=CHECK-LTO-ARMPL %s
+// CHECK-LTO-ARMPL-NOT: "-fmath-errno"
 // CHECK-LTO-ARMPL: "-plugin-opt=-vector-library=ArmPL"
+// CHECK-LTO-ARMPL-NOT: "-fmath-errno"

``````````

</details>


https://github.com/llvm/llvm-project/pull/112580