Fix a long-standing bug where Clang had a different default from GCC on

Linux and other (non-Darwin) platforms and have it use -fmath-errno by
default (for better or worse).

Darwin has seen the light here and uses -fno-math-errno by default, this
patch preserves that.

If any maintainers for a non-Linux platform would also like to opt-in to
-fno-math-errno by default, I'm happy to add folks, but we're currently
getting buts and misleading comparisons with GCC due to this difference
in behavior on Linux at least.

llvm-svn: 155607

2 files changed, 17 insertions, 11 deletions

diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index b61b8dcf2d9..13d98201597 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -1617,16 +1617,15 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
         A->getOption().getID() != options::OPT_fhonor_nans)
       CmdArgs.push_back("-menable-no-nans");
 
-  // -fno-math-errno is default.
-  bool MathErrno = false;
+  // -fno-math-errno is default on Darwin. Other platforms, -fmath-errno is the
+  // default.
+  bool MathErrno = !getToolChain().getTriple().isOSDarwin();
   if (Arg *A = Args.getLastArg(options::OPT_ffast_math,
                                options::OPT_fmath_errno,
-                               options::OPT_fno_math_errno)) {
-    if (A->getOption().getID() == options::OPT_fmath_errno) {
-      CmdArgs.push_back("-fmath-errno");
-      MathErrno = true;
-    }
-  }
+                               options::OPT_fno_math_errno))
+    MathErrno = A->getOption().getID() == options::OPT_fmath_errno;
+  if (MathErrno)
+    CmdArgs.push_back("-fmath-errno");
 
   // There are several flags which require disabling very specific
   // optimizations. Any of these being disabled forces us to turn off the
diff --git a/clang/test/Driver/fast-math.c b/clang/test/Driver/fast-math.c
index aef7cc3624d..40b60cbcd66 100644
--- a/clang/test/Driver/fast-math.c
+++ b/clang/test/Driver/fast-math.c
@@ -19,8 +19,15 @@
 // CHECK-MATH-ERRNO: "-cc1"
 // CHECK-MATH-ERRNO: "-fmath-errno"
 //
-// RUN: %clang -### -fassociative-math -freciprocal-math -fno-signed-zeros \
-// RUN:     -fno-trapping-math -c %s 2>&1 \
+// RUN: %clang -### -fmath-errno -fno-math-errno -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-MATH-ERRNO %s
+// RUN: %clang -### -target i686-apple-darwin -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-MATH-ERRNO %s
+// CHECK-NO-MATH-ERRNO: "-cc1"
+// CHECK-NO-MATH-ERRNO-NOT: "-fmath-errno"
+//
+// RUN: %clang -### -fno-math-errno -fassociative-math -freciprocal-math \
+// RUN:     -fno-signed-zeros -fno-trapping-math -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-UNSAFE-MATH %s
 // CHECK-UNSAFE-MATH: "-cc1"
 // CHECK-UNSAFE-MATH: "-menable-unsafe-fp-math"
@@ -36,7 +43,7 @@
 // RUN:   | FileCheck --check-prefix=CHECK-NO-INFS %s
 // RUN: %clang -### -ffinite-math-only -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-NANS %s
-// RUN: %clang -### -funsafe-math-optimizations -c %s 2>&1 \
+// RUN: %clang -### -funsafe-math-optimizations -fno-math-errno -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-UNSAFE-MATH %s
 //
 // One umbrella flag is *really* weird and also changes the semantics of the