[Driver] Restructure handling of -ffast-math and similar options

The way -ffast-math and the various related options to tweak floating-point
handling are handled is inflexible and rather confusing. This patch restructures
things so that we go through the options adjusting our idea of what's enabled as
we go, instead of trying to figure each individual thing out by working
backwards from the end, as this makes the behaviour of each individual option
more clear.

Doing it this way also means we get gcc-compatible behaviour for when the
__FAST_MATH__ and __FINITE_MATH_ONLY__ macros are defined, as they should depend
on the final set of features that are enabled and not just on -ffast-math and
-ffinite-math-only specifically.

Differential Revision: http://reviews.llvm.org/D30582

llvm-svn: 297837

clang/lib/Driver/ToolChains/Clang.cpp

@@ -2301,98 +2301,129 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   if (Args.hasArg(options::OPT_fsplit_stack))
     CmdArgs.push_back("-split-stacks");
 
-  // If -Ofast is the optimization level, then -ffast-math should be enabled.
-  // This alias option is being used to simplify the getLastArg logic.
-  OptSpecifier FastMathAliasOption =
-      OFastEnabled ? options::OPT_Ofast : options::OPT_ffast_math;
-
   // Handle various floating point optimization flags, mapping them to the
-  // appropriate LLVM code generation flags. The pattern for all of these is to
+  // appropriate LLVM code generation flags. This is complicated by several
-  // default off the codegen optimizations, and if any flag enables them and no
+  // "umbrella" flags, so we do this by stepping through the flags incrementally
-  // flag disables them after the flag enabling them, enable the codegen
+  // adjusting what we think is enabled/disabled, then at the end settting the
-  // optimization. This is complicated by several "umbrella" flags.
+  // LLVM flags based on the final state.
-  if (Arg *A = Args.getLastArg(
+  bool HonorInfs = true;
-          options::OPT_ffast_math, FastMathAliasOption,
+  bool HonorNans = true;
-          options::OPT_fno_fast_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_fast_math &&
-        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, FastMathAliasOption,
-          options::OPT_fno_fast_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_fast_math &&
-        A->getOption().getID() != options::OPT_fno_finite_math_only &&
-        A->getOption().getID() != options::OPT_fhonor_nans)
-      CmdArgs.push_back("-menable-no-nans");
-
   // -fmath-errno is the default on some platforms, e.g. BSD-derived OSes.
   bool MathErrno = getToolChain().IsMathErrnoDefault();
-  if (Arg *A =
+  bool AssociativeMath = false;
-          Args.getLastArg(options::OPT_ffast_math, FastMathAliasOption,
+  bool ReciprocalMath = false;
-                          options::OPT_fno_fast_math, options::OPT_fmath_errno,
+  bool SignedZeros = true;
-                          options::OPT_fno_math_errno)) {
+  bool TrappingMath = true;
-    // Turning on -ffast_math (with either flag) removes the need for MathErrno.
+  StringRef DenormalFpMath = "";
-    // However, turning *off* -ffast_math merely restores the toolchain default
+  StringRef FpContract = "";
-    // (which may be false).
+
-    if (A->getOption().getID() == options::OPT_fno_math_errno ||
+  for (Arg *A : Args) {
-        A->getOption().getID() == options::OPT_ffast_math ||
+    switch (A->getOption().getID()) {
-        A->getOption().getID() == options::OPT_Ofast)
+    // If this isn't an FP option skip the claim below
+    default:
+      continue;
+
+    // Options controlling individual features
+    case options::OPT_fhonor_infinities:    HonorInfs = true;        break;
+    case options::OPT_fno_honor_infinities: HonorInfs = false;       break;
+    case options::OPT_fhonor_nans:          HonorNans = true;        break;
+    case options::OPT_fno_honor_nans:       HonorNans = false;       break;
+    case options::OPT_fmath_errno:          MathErrno = true;        break;
+    case options::OPT_fno_math_errno:       MathErrno = false;       break;
+    case options::OPT_fassociative_math:    AssociativeMath = true;  break;
+    case options::OPT_fno_associative_math: AssociativeMath = false; break;
+    case options::OPT_freciprocal_math:     ReciprocalMath = true;   break;
+    case options::OPT_fno_reciprocal_math:  ReciprocalMath = false;  break;
+    case options::OPT_fsigned_zeros:        SignedZeros = true;      break;
+    case options::OPT_fno_signed_zeros:     SignedZeros = false;     break;
+    case options::OPT_ftrapping_math:       TrappingMath = true;     break;
+    case options::OPT_fno_trapping_math:    TrappingMath = false;    break;
+
+    case options::OPT_fdenormal_fp_math_EQ:
+      DenormalFpMath = A->getValue();
+      break;
+
+    // Validate and pass through -fp-contract option.
+    case options::OPT_ffp_contract: {
+      StringRef Val = A->getValue();
+      if (Val == "fast" || Val == "on" || Val == "off") {
+        FpContract = Val;
+      } else {
+        D.Diag(diag::err_drv_unsupported_option_argument)
+            << A->getOption().getName() << Val;
+      }
+      break;
+    }
+
+    case options::OPT_ffinite_math_only:
+      HonorInfs = false;
+      HonorNans = false;
+      break;
+    case options::OPT_fno_finite_math_only:
+      HonorInfs = true;
+      HonorNans = true;
+      break;
+
+    case options::OPT_funsafe_math_optimizations:
+      AssociativeMath = true;
+      ReciprocalMath = true;
+      SignedZeros = false;
+      TrappingMath = false;
+      break;
+    case options::OPT_fno_unsafe_math_optimizations:
+      AssociativeMath = false;
+      ReciprocalMath = false;
+      SignedZeros = true;
+      TrappingMath = true;
+      // -fno_unsafe_math_optimizations restores default denormal handling
+      DenormalFpMath = "";
+      break;
+
+    case options::OPT_Ofast:
+      // If -Ofast is the optimization level, then -ffast-math should be enabled
+      if (!OFastEnabled)
+        continue;
+      LLVM_FALLTHROUGH;
+    case options::OPT_ffast_math:
+      HonorInfs = false;
+      HonorNans = false;
       MathErrno = false;
-    else if (A->getOption().getID() == options::OPT_fmath_errno)
+      AssociativeMath = true;
-      MathErrno = true;
+      ReciprocalMath = true;
+      SignedZeros = false;
+      TrappingMath = false;
+      // If fast-math is set then set the fp-contract mode to fast.
+      FpContract = "fast";
+      break;
+    case options::OPT_fno_fast_math:
+      HonorInfs = true;
+      HonorNans = true;
+      // Turning on -ffast-math (with either flag) removes the need for
+      // MathErrno. However, turning *off* -ffast-math merely restores the
+      // toolchain default (which may be false).
+      MathErrno = getToolChain().IsMathErrnoDefault();
+      AssociativeMath = false;
+      ReciprocalMath = false;
+      SignedZeros = true;
+      TrappingMath = true;
+      // -fno_fast_math restores default denormal and fpcontract handling
+      DenormalFpMath = "";
+      FpContract = "";
+      break;
+    }
+    // If we handled this option claim it
+    A->claim();
   }
+
+  if (!HonorInfs)
+    CmdArgs.push_back("-menable-no-infs");
+
+  if (!HonorNans)
+    CmdArgs.push_back("-menable-no-nans");
+
   if (MathErrno)
     CmdArgs.push_back("-fmath-errno");
 
-  // 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, FastMathAliasOption,
-          options::OPT_fno_fast_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_fast_math &&
-        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, FastMathAliasOption,
-          options::OPT_fno_fast_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_fast_math &&
-        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, FastMathAliasOption,
-          options::OPT_fno_fast_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_fast_math &&
-        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, FastMathAliasOption,
-          options::OPT_fno_fast_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_fast_math &&
-        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");
@@ -2406,50 +2437,24 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   if (!TrappingMath)
     CmdArgs.push_back("-fno-trapping-math");
 
+  if (!DenormalFpMath.empty())
+    CmdArgs.push_back(Args.MakeArgString("-fdenormal-fp-math="+DenormalFpMath));
 
-  if (Arg *A = Args.getLastArg(options::OPT_ffast_math, FastMathAliasOption,
+  if (!FpContract.empty())
-                               options::OPT_fno_fast_math,
+    CmdArgs.push_back(Args.MakeArgString("-ffp-contract="+FpContract));
-                               options::OPT_funsafe_math_optimizations,
-                               options::OPT_fno_unsafe_math_optimizations,
-                               options::OPT_fdenormal_fp_math_EQ))
-    if (A->getOption().getID() != options::OPT_fno_fast_math &&
-        A->getOption().getID() != options::OPT_fno_unsafe_math_optimizations)
-      Args.AddLastArg(CmdArgs, options::OPT_fdenormal_fp_math_EQ);
-
-  // Validate and pass through -fp-contract option.
-  if (Arg *A = Args.getLastArg(options::OPT_ffast_math, FastMathAliasOption,
-                               options::OPT_fno_fast_math,
-                               options::OPT_ffp_contract)) {
-    if (A->getOption().getID() == options::OPT_ffp_contract) {
-      StringRef Val = A->getValue();
-      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 if (A->getOption().matches(options::OPT_ffast_math) ||
-               (OFastEnabled && A->getOption().matches(options::OPT_Ofast))) {
-      // If fast-math is set then set the fp-contract mode to fast.
-      CmdArgs.push_back(Args.MakeArgString("-ffp-contract=fast"));
-    }
-  }
 
   ParseMRecip(getToolChain().getDriver(), Args, CmdArgs);
 
-  // We separately look for the '-ffast-math' and '-ffinite-math-only' flags,
+  // -ffast-math enables the __FAST_MATH__ preprocessor macro, but check for the
-  // and if we find them, tell the frontend to provide the appropriate
+  // individual features enabled by -ffast-math instead of the option itself as
-  // preprocessor macros. This is distinct from enabling any optimizations as
+  // that's consistent with gcc's behaviour.
-  // these options induce language changes which must survive serialization
+  if (!HonorInfs && !HonorNans && !MathErrno && AssociativeMath &&
-  // and deserialization, etc.
+      ReciprocalMath && !SignedZeros && !TrappingMath)
-  if (Arg *A = Args.getLastArg(options::OPT_ffast_math, FastMathAliasOption,
+    CmdArgs.push_back("-ffast-math");
-                               options::OPT_fno_fast_math))
+
-    if (!A->getOption().matches(options::OPT_fno_fast_math))
+  // Handle __FINITE_MATH_ONLY__ similarly.
-      CmdArgs.push_back("-ffast-math");
+  if (!HonorInfs && !HonorNans)
-  if (Arg *A = Args.getLastArg(options::OPT_ffinite_math_only,
+    CmdArgs.push_back("-ffinite-math-only");
-                               options::OPT_fno_fast_math))
-    if (A->getOption().matches(options::OPT_ffinite_math_only))
-      CmdArgs.push_back("-ffinite-math-only");
 
   // Decide whether to use verbose asm. Verbose assembly is the default on
   // toolchains which have the integrated assembler on by default.

clang/test/Driver/fast-math.c

@@ -148,20 +148,31 @@
 //
 // One umbrella flag is *really* weird and also changes the semantics of the
 // program by adding a special preprocessor macro. Check that the frontend flag
-// modeling this semantic change is provided. Also check that the semantic
+// modeling this semantic change is provided. Also check that the flag is not
-// impact remains even if every optimization is disabled.
+// present if any of the optimization is disabled.
 // RUN: %clang -### -ffast-math -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-FAST-MATH %s
 // RUN: %clang -### -fno-fast-math -ffast-math -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-FAST-MATH %s
-// RUN: %clang -### -ffast-math -fno-finite-math-only \
+// RUN: %clang -### -funsafe-math-optimizations -ffinite-math-only \
-// RUN:     -fno-unsafe-math-optimizations -fmath-errno -c %s 2>&1 \
+// RUN:     -fno-math-errno -ffp-contract=fast -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-FAST-MATH %s
+// RUN: %clang -### -fno-honor-infinities -fno-honor-nans -fno-math-errno \
+// RUN:     -fassociative-math -freciprocal-math -fno-signed-zeros \
+// RUN:     -fno-trapping-math -ffp-contract=fast -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-FAST-MATH %s
 // CHECK-FAST-MATH: "-cc1"
 // CHECK-FAST-MATH: "-ffast-math"
+// CHECK-FAST-MATH: "-ffinite-math-only"
 //
 // RUN: %clang -### -ffast-math -fno-fast-math -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-FAST-MATH %s
+// RUN: %clang -### -ffast-math -fno-finite-math-only -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-FAST-MATH %s
+// RUN: %clang -### -ffast-math -fno-unsafe-math-optimizations -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-FAST-MATH %s
+// RUN: %clang -### -ffast-math -fmath-errno -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-FAST-MATH %s
 // CHECK-NO-FAST-MATH: "-cc1"
 // CHECK-NO-FAST-MATH-NOT: "-ffast-math"
 //
@@ -179,6 +190,7 @@
 // RUN:   | FileCheck --check-prefix=CHECK-NO-NO-INFS %s
 // CHECK-NO-NO-INFS: "-cc1"
 // CHECK-NO-NO-INFS-NOT: "-menable-no-infs"
+// CHECK-NO-NO-INFS-NOT: "-ffinite-math-only"
 // CHECK-NO-NO-INFS: "-o"
 //
 // RUN: %clang -### -fno-honor-nans -fhonor-nans -c %s 2>&1 \
@@ -193,6 +205,7 @@
 // RUN:   | FileCheck --check-prefix=CHECK-NO-NO-NANS %s
 // CHECK-NO-NO-NANS: "-cc1"
 // CHECK-NO-NO-NANS-NOT: "-menable-no-nans"
+// CHECK-NO-NO-NANS-NOT: "-ffinite-math-only"
 // CHECK-NO-NO-NANS: "-o"
 //
 // RUN: %clang -### -fassociative-math -freciprocal-math -fno-signed-zeros \