[clang] set __NO_MATH_ERRNO__ if -fno-math-errno

[alxu]

Summary

This causes modern glibc to unset math_errhandling MATH_ERRNO. gcc 12 also sets some other macros, but most of them are associated with flags ignored by clang, so without library examples, it is difficult to determine whether they should be set. I think setting this one macro is OK for now.

[aaron.ballman]

Thanks for this! I'm adding some more reviewers to the list to help get this reviewed.

The patch doesn't seem to apply cleanly, so precommit CI isn't running on it. Can you rectify that? Also, the change needs test coverage of some kind.

clang/lib/Frontend/InitPreprocessor.cpp

1022 ↗

(On Diff #396416)

Does GCC gate on -ffast-math? My testing suggests that -fno-math-errno alone is what sets this macro in GCC.

[alxu]

In D116337#3217955, @aaron.ballman wrote:

Thanks for this! I'm adding some more reviewers to the list to help get this reviewed.

The patch doesn't seem to apply cleanly, so precommit CI isn't running on it. Can you rectify that?

GNU patch applies the patch with offset 20 and no fuzz on llvm-project main. However, I have included a rebase from llvm 13 to llvm main along with the tests in the new patch.

Also, the change needs test coverage of some kind.

Added.

[alxu]

clang/lib/Frontend/InitPreprocessor.cpp

1022 ↗

(On Diff #396416)

I thought that MathErrno was not set if -ffast-math is specified, but that is apparently not true. It looks like lib/Driver/ToolChains/Clang.cpp should set FiniteMathOnly for -ffast-math, and the check below should be adjusted; otherwise it is wrong for -ffast-math -fno-finite-math-only.

[alxu]

Try -p1 compatible diff.

[alxu]

Sort test defines orthographically, not chronologically.

[aaron.ballman]

It looks like precommit CI is still failing on Clang :: Preprocessor/predefined-macros.c on Windows (the Debian failures look unrelated, but you should double-check just to be sure).

https://buildkite.com/llvm-project/premerge-checks/builds/72399#4ba61c84-15ff-462e-b861-8b7be5b09eb4

Also, when you submit the patch, can you use -U9999 to provide a bunch of context in the patch file? That makes code review easier within Phab.

[alxu]

Correct logic, increase context.

[aaron.ballman]

Getting closer! Now there are new CI pipeline failures (some tests look like they need updating).

[alxu]

Update init.c, init-aarch64.c tests.

[alxu]

Re-add context lines.

[aaron.ballman]

There we go, now precommit CI is happy; LGTM!

[alxu]

I don't have commit access; can someone commit this for me? Please use author "Alex Xu (Hello71) <[e-mail]>". Thanks!

[aaron.ballman]

Thanks for the patch! I've landed on your behalf in f282b6809105075b65974989459ee420ecd406e9.

clang/lib/Frontend/InitPreprocessor.cpp

#undef TOSTR2
   DefineFastIntType(16, false, TI, Builder);
   DefineFastIntType(32, true, TI, Builder);
   DefineFastIntType(32, false, TI, Builder);
   DefineFastIntType(64, true, TI, Builder);
   DefineFastIntType(64, false, TI, Builder);
 
   Builder.defineMacro("__USER_LABEL_PREFIX__", TI.getUserLabelPrefix());
 
+  if (!LangOpts.MathErrno)
+    Builder.defineMacro("__NO_MATH_ERRNO__");
+
   if (LangOpts.FastMath || LangOpts.FiniteMathOnly)
     Builder.defineMacro("__FINITE_MATH_ONLY__", "1");
   else
     Builder.defineMacro("__FINITE_MATH_ONLY__", "0");
 
   if (LangOpts.GNUCVersion) {
     if (LangOpts.GNUInline || LangOpts.CPlusPlus)
       Builder.defineMacro("__GNUC_GNU_INLINE__");

clang/test/Preprocessor/init-aarch64.c

 // AARCH64-NEXT: #define __LDBL_MIN_10_EXP__ (-4931)
 // AARCH64-NEXT: #define __LDBL_MIN_EXP__ (-16381)
 // AARCH64-NEXT: #define __LDBL_MIN__ 3.36210314311209350626267781732175260e-4932L
 // AARCH64_LE-NEXT: #define __LITTLE_ENDIAN__ 1
 // AARCH64-NEXT: #define __LONG_LONG_MAX__ 9223372036854775807LL
 // AARCH64-NEXT: #define __LONG_MAX__ 9223372036854775807L
 // AARCH64-NEXT: #define __LP64__ 1
 // AARCH64-NEXT: #define __NO_INLINE__ 1
+// AARCH64-NEXT: #define __NO_MATH_ERRNO__ 1
 // AARCH64-NEXT: #define __OBJC_BOOL_IS_BOOL 0
 // AARCH64-NEXT: #define __OPENCL_MEMORY_SCOPE_ALL_SVM_DEVICES 3
 // AARCH64-NEXT: #define __OPENCL_MEMORY_SCOPE_DEVICE 2
 // AARCH64-NEXT: #define __OPENCL_MEMORY_SCOPE_SUB_GROUP 4
 // AARCH64-NEXT: #define __OPENCL_MEMORY_SCOPE_WORK_GROUP 1
 // AARCH64-NEXT: #define __OPENCL_MEMORY_SCOPE_WORK_ITEM 0
 // AARCH64-NEXT: #define __ORDER_BIG_ENDIAN__ 4321
 // AARCH64-NEXT: #define __ORDER_LITTLE_ENDIAN__ 1234

clang/test/Preprocessor/init.c

 // WEBASSEMBLY-NEXT:#define __LDBL_MIN__ 3.36210314311209350626267781732175260e-4932L
 // WEBASSEMBLY-NEXT:#define __LITTLE_ENDIAN__ 1
 // WEBASSEMBLY-NEXT:#define __LONG_LONG_MAX__ 9223372036854775807LL
 // WEBASSEMBLY32-NEXT:#define __LONG_MAX__ 2147483647L
 // WEBASSEMBLY32-NOT:#define __LP64__
 // WEBASSEMBLY64-NEXT:#define __LONG_MAX__ 9223372036854775807L
 // WEBASSEMBLY64-NEXT:#define __LP64__ 1
 // WEBASSEMBLY-NEXT:#define __NO_INLINE__ 1
+// WEBASSEMBLY-NEXT:#define __NO_MATH_ERRNO__ 1
 // WEBASSEMBLY-NEXT:#define __OBJC_BOOL_IS_BOOL 0
 // WEBASSEMBLY-NEXT:#define __OPENCL_MEMORY_SCOPE_ALL_SVM_DEVICES 3
 // WEBASSEMBLY-NEXT:#define __OPENCL_MEMORY_SCOPE_DEVICE 2
 // WEBASSEMBLY-NEXT:#define __OPENCL_MEMORY_SCOPE_SUB_GROUP 4
 // WEBASSEMBLY-NEXT:#define __OPENCL_MEMORY_SCOPE_WORK_GROUP 1
 // WEBASSEMBLY-NEXT:#define __OPENCL_MEMORY_SCOPE_WORK_ITEM 0
 // WEBASSEMBLY-NEXT:#define __ORDER_BIG_ENDIAN__ 4321
 // WEBASSEMBLY-NEXT:#define __ORDER_LITTLE_ENDIAN__ 1234

clang/test/Preprocessor/predefined-macros.c

 // CHECK-MS-STDINT:#define __UINT_LEAST64_TYPE__ long long unsigned int
 // CHECK-MS-STDINT:#define __UINT_LEAST8_MAX__ 255
 // CHECK-MS-STDINT:#define __UINT_LEAST8_TYPE__ unsigned char
 //
 // RUN: %clang_cc1 %s -E -dM -ffast-math -o - \
 // RUN:   | FileCheck -match-full-lines %s --check-prefix=CHECK-FAST-MATH
 // CHECK-FAST-MATH: #define __FAST_MATH__ 1
 // CHECK-FAST-MATH: #define __FINITE_MATH_ONLY__ 1
+// CHECK-FAST-MATH: #define __NO_MATH_ERRNO__ 1
+//
+// RUN: %clang_cc1 %s -E -dM -fmath-errno -o - \
+// RUN:   | FileCheck -match-full-lines %s --check-prefix=CHECK-MATH-ERRNO
+// CHECK-MATH-ERRNO-NOT: __NO_MATH_ERRNO__
+//
+// RUN: %clang %s -E -dM -fno-math-errno -o - \
+// RUN:   | FileCheck -match-full-lines %s --check-prefix=CHECK-NO-MATH-ERRNO
+// CHECK-NO-MATH-ERRNO: #define __NO_MATH_ERRNO__ 1
 //
 // RUN: %clang_cc1 %s -E -dM -ffinite-math-only -o - \
 // RUN:   | FileCheck -match-full-lines %s --check-prefix=CHECK-FINITE-MATH-ONLY
 // CHECK-FINITE-MATH-ONLY: #define __FINITE_MATH_ONLY__ 1
 //
 // RUN: %clang %s -E -dM -fno-finite-math-only -o - \
 // RUN:   | FileCheck -match-full-lines %s --check-prefix=CHECK-NO-FINITE-MATH-ONLY
 // CHECK-NO-FINITE-MATH-ONLY: #define __FINITE_MATH_ONLY__ 0