Driver: Turn the default value for -fmath-errno into a proper target hook and disable it by default on more platforms.

For now -fno-math-errno is the default on BSD-derived platforms (Darwin,
DragonFlyBSD, FreeBSD, NetBSD, OpenBSD). If the default is not right for
your platform, please yell. I only verified the result with the default
compilers on Darwin and FreeBSD.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@155990 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Driver/ToolChain.h

@@ -137,6 +137,9 @@ public:
   /// default.
   virtual bool IsStrictAliasingDefault() const { return true; }
 
+  /// IsMathErrnoDefault - Does this tool chain use -fmath-errno by default.
+  virtual bool IsMathErrnoDefault() const { return true; }
+
   /// IsObjCDefaultSynthPropertiesDefault - Does this tool chain enable
   /// -fobjc-default-synthesize-properties by default.
   virtual bool IsObjCDefaultSynthPropertiesDefault() const { return false; }

lib/Driver/ToolChains.h

@@ -334,6 +334,10 @@ public:
 #endif
   }
 
+  virtual bool IsMathErrnoDefault() const {
+    return false;
+  }
+
   virtual bool IsObjCDefaultSynthPropertiesDefault() const {
     return true;
   }
@@ -459,6 +463,7 @@ class LLVM_LIBRARY_VISIBILITY OpenBSD : public Generic_ELF {
 public:
   OpenBSD(const Driver &D, const llvm::Triple& Triple, const ArgList &Args);
 
+  virtual bool IsMathErrnoDefault() const { return false; }
   virtual bool IsObjCNonFragileABIDefault() const { return true; }
   virtual bool IsObjCLegacyDispatchDefault() const {
     llvm::Triple::ArchType Arch = getTriple().getArch();
@@ -477,6 +482,7 @@ class LLVM_LIBRARY_VISIBILITY FreeBSD : public Generic_ELF {
 public:
   FreeBSD(const Driver &D, const llvm::Triple& Triple, const ArgList &Args);
 
+  virtual bool IsMathErrnoDefault() const { return false; }
   virtual bool IsObjCNonFragileABIDefault() const { return true; }
   virtual bool IsObjCLegacyDispatchDefault() const {
     llvm::Triple::ArchType Arch = getTriple().getArch();
@@ -495,6 +501,7 @@ class LLVM_LIBRARY_VISIBILITY NetBSD : public Generic_ELF {
 public:
   NetBSD(const Driver &D, const llvm::Triple& Triple, const ArgList &Args);
 
+  virtual bool IsMathErrnoDefault() const { return false; }
   virtual bool IsObjCNonFragileABIDefault() const { return true; }
   virtual bool IsObjCLegacyDispatchDefault() const {
     llvm::Triple::ArchType Arch = getTriple().getArch();
@@ -521,6 +528,8 @@ class LLVM_LIBRARY_VISIBILITY DragonFly : public Generic_ELF {
 public:
   DragonFly(const Driver &D, const llvm::Triple& Triple, const ArgList &Args);
 
+  virtual bool IsMathErrnoDefault() const { return false; }
+
   virtual Tool &SelectTool(const Compilation &C, const JobAction &JA,
                            const ActionList &Inputs) const;
 };

lib/Driver/Tools.cpp

@@ -1617,9 +1617,8 @@ 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 on Darwin. Other platforms, -fmath-errno is the
-  // default.
-  bool MathErrno = !getToolChain().getTriple().isOSDarwin();
+  // -fmath-errno is the default on some platforms, e.g. BSD-derived OSes.
+  bool MathErrno = getToolChain().IsMathErrnoDefault();
   if (Arg *A = Args.getLastArg(options::OPT_ffast_math,
                                options::OPT_fmath_errno,
                                options::OPT_fno_math_errno))

test/Driver/fast-math.c

@@ -26,6 +26,14 @@
 // 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
+// RUN: %clang -### -target x86_64-unknown-freebsd -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-MATH-ERRNO %s
+// RUN: %clang -### -target x86_64-unknown-netbsd -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-MATH-ERRNO %s
+// 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
 // CHECK-NO-MATH-ERRNO: "-cc1"
 // CHECK-NO-MATH-ERRNO-NOT: "-fmath-errno"
 //