Process the -freciprocal-math optimization flag (PR20912)

The driver currently accepts but ignores the -freciprocal-math flag.
This patch passes the flag through and enables 'arcp' fast-math-flag
generation in IR.

Note that this change does not actually enable the optimization for
any target. The reassociation optimization that this flag specifies
was implemented by http://reviews.llvm.org/D6334 :
http://llvm.org/viewvc/llvm-project?view=revision&revision=222510

Because the optimization is done in the backend rather than IR,
the backend must be modified to understand instruction-level
fast-math-flags or a new function-level attribute must be created.

Also note that -freciprocal-math is independent of any target-specific
usage of reciprocal estimate hardware instructions. That requires
its own flag ('-mrecip').

https://llvm.org/bugs/show_bug.cgi?id=20912

llvm-svn: 234493

3 files changed, 7 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index e59a50ee76c..8401d722f42 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -70,6 +70,9 @@ CodeGenFunction::CodeGenFunction(CodeGenModule &cgm, bool suppressNewContext)
   if (CGM.getCodeGenOpts().NoSignedZeros) {
     FMF.setNoSignedZeros();
   }
+  if (CGM.getCodeGenOpts().ReciprocalMath) {
+    FMF.setAllowReciprocal();
+  }
   Builder.SetFastMathFlags(FMF);
 }
 
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index f0fc574bd01..9ebf681aabd 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -3062,6 +3062,9 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   if (!SignedZeros)
     CmdArgs.push_back("-fno-signed-zeros");
 
+  if (ReciprocalMath)
+    CmdArgs.push_back("-freciprocal-math");
+
   // Validate and pass through -fp-contract option. 
   if (Arg *A = Args.getLastArg(options::OPT_ffast_math, FastMathAliasOption,
                                options::OPT_fno_fast_math,
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 5d2cdae6e00..cd0a7c4640c 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -451,6 +451,7 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
                        Args.hasArg(OPT_cl_finite_math_only) ||
                        Args.hasArg(OPT_cl_fast_relaxed_math));
   Opts.NoSignedZeros = Args.hasArg(OPT_fno_signed_zeros);
+  Opts.ReciprocalMath = Args.hasArg(OPT_freciprocal_math);
   Opts.NoZeroInitializedInBSS = Args.hasArg(OPT_mno_zero_initialized_in_bss);
   Opts.BackendOptions = Args.getAllArgValues(OPT_backend_option);
   Opts.NumRegisterParameters = getLastArgIntValue(Args, OPT_mregparm, 0, Diags);