Partially revert fa7cd54.

The guessing of whether or not FTZ/DAZ mode would be enabled is
insufficiently accurate.

Author: jcranmer-intel

clang/lib/Driver/ToolChains/Linux.cpp

@@ -842,25 +842,6 @@ void Linux::addProfileRTLibs(const llvm::opt::ArgList &Args,
   ToolChain::addProfileRTLibs(Args, CmdArgs);
 }
 
-llvm::DenormalMode
-Linux::getDefaultDenormalModeForType(const llvm::opt::ArgList &DriverArgs,
-                                     const JobAction &JA,
-                                     const llvm::fltSemantics *FPType) const {
-  switch (getTriple().getArch()) {
-  case llvm::Triple::x86:
-  case llvm::Triple::x86_64: {
-    std::string Unused;
-    // DAZ and FTZ are turned on in crtfastmath.o
-    if (!DriverArgs.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles) &&
-        isFastMathRuntimeAvailable(DriverArgs, Unused))
-      return llvm::DenormalMode::getPreserveSign();
-    return llvm::DenormalMode::getIEEE();
-  }
-  default:
-    return llvm::DenormalMode::getIEEE();
-  }
-}
-
 void Linux::addExtraOpts(llvm::opt::ArgStringList &CmdArgs) const {
   for (const auto &Opt : ExtraOpts)
     CmdArgs.push_back(Opt.c_str());

clang/lib/Driver/ToolChains/Linux.h

@@ -59,10 +59,6 @@ class LLVM_LIBRARY_VISIBILITY Linux : public Generic_ELF {
 
   std::vector<std::string> ExtraOpts;
 
-  llvm::DenormalMode getDefaultDenormalModeForType(
-      const llvm::opt::ArgList &DriverArgs, const JobAction &JA,
-      const llvm::fltSemantics *FPType = nullptr) const override;
-
   const char *getDefaultLinker() const override;
 
 protected:

clang/test/Driver/default-denormal-fp-math.c

@@ -3,15 +3,6 @@
 
 // RUN: %clang -### -target x86_64-unknown-linux-gnu --sysroot=%S/Inputs/basic_linux_tree -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
 
-// crtfastmath enables ftz and daz
-// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffast-math --sysroot=%S/Inputs/basic_linux_tree -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-PRESERVESIGN %s
-
-// crt not linked in with nostartfiles
-// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffast-math -nostartfiles --sysroot=%S/Inputs/basic_linux_tree -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
-
-// If there's no crtfastmath, don't assume ftz/daz
-// RUN: %clang -### -target x86_64-unknown-linux-gnu -ffast-math --sysroot=/dev/null -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-IEEE %s
-
 // RUN: %clang -### -target x86_64-scei-ps4 -c %s -v 2>&1 | FileCheck -check-prefix=CHECK-PRESERVESIGN %s
 
 // Flag omitted for default