Add -ffp-contract = { fast | on | off } command line option support.

This flag sets the 'fp-contract' mode, which controls the formation of fused
floating point operations. Available modes are:

- Fast: Form fused operations anywhere. 
- On: Form fused operations where allowed by FP_CONTRACT. This is the default
      mode.
- Off: Don't form fused operations (in future this may be relaxed to forming
       fused operations where it can be proved that the result won't be
       affected).

Currently clang doesn't support the FP_CONTRACT pragma, so the 'On' and 'Off'
modes are equivalent.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@159794 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 48 insertions, 0 deletions

diff --git a/lib/CodeGen/BackendUtil.cpp b/lib/CodeGen/BackendUtil.cpp
index 5a97875ef4..0a1915b485 100644
--- a/lib/CodeGen/BackendUtil.cpp
+++ b/lib/CodeGen/BackendUtil.cpp
@@ -351,6 +351,19 @@ bool EmitAssemblyHelper::AddEmitPasses(BackendAction Action,
     Options.FloatABIType = llvm::FloatABI::Default;
   }
 
+  // Set FP fusion mode.
+  switch (LangOpts.getFPContractMode()) {
+  case LangOptions::FPC_Off:
+    Options.AllowFPOpFusion = llvm::FPOpFusion::Strict;
+    break;
+  case LangOptions::FPC_On:
+    Options.AllowFPOpFusion = llvm::FPOpFusion::Standard;
+    break;
+  case LangOptions::FPC_Fast:
+    Options.AllowFPOpFusion = llvm::FPOpFusion::Fast;
+    break;              
+  }
+
   Options.LessPreciseFPMADOption = CodeGenOpts.LessPreciseFPMAD;
   Options.NoInfsFPMath = CodeGenOpts.NoInfsFPMath;
   Options.NoNaNsFPMath = CodeGenOpts.NoNaNsFPMath;
diff --git a/lib/Driver/Tools.cpp b/lib/Driver/Tools.cpp
index 98beb2234a..dd198a1e9d 100644
--- a/lib/Driver/Tools.cpp
+++ b/lib/Driver/Tools.cpp
@@ -1805,6 +1805,24 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
       !TrappingMath)
     CmdArgs.push_back("-menable-unsafe-fp-math");
 
+
+  // Validate and pass through -fp-contract option. 
+  if (Arg *A = Args.getLastArg(options::OPT_ffast_math,
+                               options::OPT_ffp_contract)) {
+    if (A->getOption().getID() == options::OPT_ffp_contract) {
+      StringRef Val = A->getValue(Args);
+      if (Val == "fast" || Val == "on" || Val == "off") {
+        CmdArgs.push_back(Args.MakeArgString("-ffp-contract=" + Val));
+      } else {
+        D.Diag(diag::err_drv_unsupported_option_argument)
+          << A->getOption().getName() << Val;
+      }
+    } else { // A is OPT_ffast_math
+      // If fast-math is set then set the fp-contract mode to fast.
+      CmdArgs.push_back(Args.MakeArgString("-ffp-contract=fast"));
+    }
+  }
+
   // We separately look for the '-ffast-math' flag, and if we find it, tell the
   // frontend to provide the appropriate preprocessor macros. This is distinct
   // from enabling any optimizations as it induces a language change which must
diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index 943cb20e2d..cf08913e3b 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -759,6 +759,11 @@ static void LangOptsToArgs(const LangOptions &Opts, ToArgsList &Res) {
       Res.push_back("-ftrapv-handler", Opts.OverflowHandler);
     break;
   }
+  switch (Opts.getFPContractMode()) {
+  case LangOptions::FPC_Off:  Res.push_back("-ffp-contract=off"); break;
+  case LangOptions::FPC_On:   Res.push_back("-ffp-contract=on"); break;
+  case LangOptions::FPC_Fast: Res.push_back("-ffp-contract=fast"); break;
+  }
   if (Opts.HeinousExtensions)
     Res.push_back("-fheinous-gnu-extensions");
   // Optimize is implicit.
@@ -1975,6 +1980,18 @@ static void ParseLangArgs(LangOptions &Opts, ArgList &Args, InputKind IK,
     Diags.Report(diag::err_drv_invalid_value)
       << Args.getLastArg(OPT_fvisibility)->getAsString(Args) << Vis;
 
+  if (Arg *A = Args.getLastArg(OPT_ffp_contract)) {
+    StringRef Val = A->getValue(Args);
+    if (Val == "fast")
+      Opts.setFPContractMode(LangOptions::FPC_Fast);
+    else if (Val == "on")
+      Opts.setFPContractMode(LangOptions::FPC_On);
+    else if (Val == "off")
+      Opts.setFPContractMode(LangOptions::FPC_Off);
+    else
+      Diags.Report(diag::err_drv_invalid_value) << A->getAsString(Args) << Val;
+  }
+
   if (Args.hasArg(OPT_fvisibility_inlines_hidden))
     Opts.InlineVisibilityHidden = 1;