Fix PR11685 by implementing -ffast-math and its various friends in the

Clang driver. This involves a bunch of silly option parsing code to try
to carefully emulate GCC's options. Currently, this takes a conservative
approach, and unless all of the unsafe optimizations are enabled, none
of them are. The fine grained control doesn't seem particularly useful.
If it ever becomes useful, we can add that to LLVM first, and then
expose it here.

This also fixes a few tiny bugs in the flag management around
-fhonor-infinities and -fhonor-nans; the flags now form proper sets both
for enabling and disabling, with the last flag winning.

I've also implemented a moderately terrifying GCC feature where
a language change is also provided by the '-ffast-math' flag by defining
the __FAST_MATH__ preprocessor macro. This feature is tracked and
serialized in the frontend but it isn't used yet. A subsequent patch
will add the preprocessor macro and tests for it.

I've manually tested that codegen appears to respect this, but I've not
dug in enough to see if there is an easy way to test codegen options w/o
relying on the particulars of LLVM's optimizations.

llvm-svn: 147434

1 files changed, 84 insertions, 18 deletions

diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index 41ff1102bfc..f678667c33c 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -1435,18 +1435,90 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
                     getToolChain().IsStrictAliasingDefault()))
     CmdArgs.push_back("-relaxed-aliasing");
 
-  // Handle -f{no-}honor-infinities, -f{no-}honor-nans, and -ffinite-math-only.
-  bool HonorInfinities = Args.hasFlag(options::OPT_fhonor_infinities,
-                                      options::OPT_fno_honor_infinities);
-  bool HonorNaNs = Args.hasFlag(options::OPT_fhonor_nans,
-                                options::OPT_fno_honor_nans);
-  if (Args.hasArg(options::OPT_ffinite_math_only))
-    HonorInfinities = HonorNaNs = false;
-  if (!HonorInfinities)
-    CmdArgs.push_back("-menable-no-infs");
-  if (!HonorNaNs)
-    CmdArgs.push_back("-menable-no-nans");
-    
+  // Handle various floating point optimization flags, mapping them to the
+  // appropriate LLVM code generation flags. The pattern for all of these is to
+  // default off the codegen optimizations, and if any flag enables them and no
+  // flag disables them after the flag enabling them, enable the codegen
+  // optimization. This is complicated by several "umbrella" flags.
+  if (Arg *A = Args.getLastArg(options::OPT_ffast_math,
+                               options::OPT_ffinite_math_only,
+                               options::OPT_fno_finite_math_only,
+                               options::OPT_fhonor_infinities,
+                               options::OPT_fno_honor_infinities))
+    if (A->getOption().getID() != options::OPT_fno_finite_math_only &&
+        A->getOption().getID() != options::OPT_fhonor_infinities)
+      CmdArgs.push_back("-menable-no-infs");
+  if (Arg *A = Args.getLastArg(options::OPT_ffast_math,
+                               options::OPT_ffinite_math_only,
+                               options::OPT_fno_finite_math_only,
+                               options::OPT_fhonor_nans,
+                               options::OPT_fno_honor_nans))
+    if (A->getOption().getID() != options::OPT_fno_finite_math_only &&
+        A->getOption().getID() != options::OPT_fhonor_nans)
+      CmdArgs.push_back("-menable-no-nans");
+
+  // -fno-math-errno is default.
+  bool MathErrno = false;
+  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;
+    }
+  }
+
+  // There are several flags which require disabling very specific
+  // optimizations. Any of these being disabled forces us to turn off the
+  // entire set of LLVM optimizations, so collect them through all the flag
+  // madness.
+  bool AssociativeMath = false;
+  if (Arg *A = Args.getLastArg(options::OPT_ffast_math,
+                               options::OPT_funsafe_math_optimizations,
+                               options::OPT_fno_unsafe_math_optimizations,
+                               options::OPT_fassociative_math,
+                               options::OPT_fno_associative_math))
+    if (A->getOption().getID() != options::OPT_fno_unsafe_math_optimizations &&
+        A->getOption().getID() != options::OPT_fno_associative_math)
+      AssociativeMath = true;
+  bool ReciprocalMath = false;
+  if (Arg *A = Args.getLastArg(options::OPT_ffast_math,
+                               options::OPT_funsafe_math_optimizations,
+                               options::OPT_fno_unsafe_math_optimizations,
+                               options::OPT_freciprocal_math,
+                               options::OPT_fno_reciprocal_math))
+    if (A->getOption().getID() != options::OPT_fno_unsafe_math_optimizations &&
+        A->getOption().getID() != options::OPT_fno_reciprocal_math)
+      ReciprocalMath = true;
+  bool SignedZeros = true;
+  if (Arg *A = Args.getLastArg(options::OPT_ffast_math,
+                               options::OPT_funsafe_math_optimizations,
+                               options::OPT_fno_unsafe_math_optimizations,
+                               options::OPT_fsigned_zeros,
+                               options::OPT_fno_signed_zeros))
+    if (A->getOption().getID() != options::OPT_fno_unsafe_math_optimizations &&
+        A->getOption().getID() != options::OPT_fsigned_zeros)
+      SignedZeros = false;
+  bool TrappingMath = true;
+  if (Arg *A = Args.getLastArg(options::OPT_ffast_math,
+                               options::OPT_funsafe_math_optimizations,
+                               options::OPT_fno_unsafe_math_optimizations,
+                               options::OPT_ftrapping_math,
+                               options::OPT_fno_trapping_math))
+    if (A->getOption().getID() != options::OPT_fno_unsafe_math_optimizations &&
+        A->getOption().getID() != options::OPT_ftrapping_math)
+      TrappingMath = false;
+  if (!MathErrno && AssociativeMath && ReciprocalMath && !SignedZeros &&
+      !TrappingMath)
+    CmdArgs.push_back("-menable-unsafe-fp-math");
+
+  // 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
+  // survive serialization and deserialization, etc.
+  if (Args.hasArg(options::OPT_ffast_math))
+    CmdArgs.push_back("-ffast-math");
+
   // Decide whether to use verbose asm. Verbose assembly is the default on
   // toolchains which have the integrated assembler on by default.
   bool IsVerboseAsmDefault = getToolChain().IsIntegratedAssemblerDefault();
@@ -1548,12 +1620,6 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
                    !getToolChain().getTriple().isOSDarwin()))
     CmdArgs.push_back("-momit-leaf-frame-pointer");
 
-  // -fno-math-errno is default.
-  if (Args.hasFlag(options::OPT_fmath_errno,
-                   options::OPT_fno_math_errno,
-                   false))
-    CmdArgs.push_back("-fmath-errno");
-
   // Explicitly error on some things we know we don't support and can't just
   // ignore.
   types::ID InputType = Inputs[0].getType();