process the -fno-signed-zeros optimization flag (PR20870)

[spatel]

Summary

The driver currently accepts but ignores the -fno-signed-zeros flag. This patch passes the flag through and enables 'nsz' fast-math-flag generation in IR.

This should resolve bug 20870 ( http://llvm.org/bugs/show_bug.cgi?id=20870 ); patches for the optimizer were checked in at:
http://llvm.org/viewvc/llvm-project?view=revision&revision=225050
http://llvm.org/viewvc/llvm-project?view=revision&revision=224583

[spatel]

Ping.

[spatel]

Ping * 2.

I haven't waded into cfe before this, so if there's someone better to take a look at this patch, please let me know. Thanks!

[rsmith]

lib/Frontend/CompilerInvocation.cpp

429–430

We generally try to keep our -cc1 interface simple and minimal. Can we remove the OPT_cl_no_signed_zeros option, and instead create -fno-signed-zeros in the CL case from the driver?

[spatel]

lib/Frontend/CompilerInvocation.cpp

429–430

Sure, that seems reasonable. It looks like we can accomplish this using an Alias in the td file. I'll update the patch.

[spatel]

Changed existing cc1 OpenCL opt for no_unsigned_zeros to be an alias of the driver option for no_unsigned_zeros.

AFAICT, this preserves the outward interface; please let me know if you see any problems.

[rsmith]

We have no backwards-compatibility constraints for our -cc1 interface, so we don't need to keep around the -cl-no-signed-zeros flag. Anyway, this patch LGTM

[spatel]

In D6873#112504, @rsmith wrote:

We have no backwards-compatibility constraints for our -cc1 interface, so we don't need to keep around the -cl-no-signed-zeros flag.

Thanks, Richard! I didn't realize we could just nuke that flag. I went ahead and checked in the patch as-is (r226915), but I can get rid of the cl flag in a subsequent patch. Looks like we can do that for a few of those cl FP flags in one patch.

include/clang/Driver/Options.td

def fno_unsafe_math_optimizations : Flag<["-"], "fno-unsafe-math-optimizations">,
   Group<f_Group>;
 def fassociative_math : Flag<["-"], "fassociative-math">, Group<f_Group>;
 def fno_associative_math : Flag<["-"], "fno-associative-math">, Group<f_Group>;
 def freciprocal_math : Flag<["-"], "freciprocal-math">, Group<f_Group>;
 def fno_reciprocal_math : Flag<["-"], "fno-reciprocal-math">, Group<f_Group>;
 def ffinite_math_only : Flag<["-"], "ffinite-math-only">, Group<f_Group>, Flags<[CC1Option]>;
 def fno_finite_math_only : Flag<["-"], "fno-finite-math-only">, Group<f_Group>;
 def fsigned_zeros : Flag<["-"], "fsigned-zeros">, Group<f_Group>;
-def fno_signed_zeros : Flag<["-"], "fno-signed-zeros">, Group<f_Group>;
+def fno_signed_zeros :
+  Flag<["-"], "fno-signed-zeros">, Group<f_Group>, Flags<[CC1Option]>,
+  HelpText<"Allow optimizations that ignore the sign of floating point zeros">;
 def fhonor_nans : Flag<["-"], "fhonor-nans">, Group<f_Group>;
 def fno_honor_nans : Flag<["-"], "fno-honor-nans">, Group<f_Group>;
 def fhonor_infinities : Flag<["-"], "fhonor-infinities">, Group<f_Group>;
 def fno_honor_infinities : Flag<["-"], "fno-honor-infinities">, Group<f_Group>;
 // This option was originally misspelt "infinites" [sic].
 def : Flag<["-"], "fhonor-infinites">, Alias<fhonor_infinities>;
 def : Flag<["-"], "fno-honor-infinites">, Alias<fno_honor_infinities>;
 def ftrapping_math : Flag<["-"], "ftrapping-math">, Group<f_Group>;

lib/Driver/Tools.cpp

if (Arg *A = Args.getLastArg(options::OPT_ffast_math, FastMathAliasOption,
     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");
 
+  if (!SignedZeros)
+    CmdArgs.push_back("-fno-signed-zeros");
 
   // 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") {

lib/Frontend/CompilerInvocation.cpp

static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   Opts.LimitFloatPrecision = Args.getLastArgValue(OPT_mlimit_float_precision);
   Opts.NoInfsFPMath = (Args.hasArg(OPT_menable_no_infinities) ||
                        Args.hasArg(OPT_cl_finite_math_only) ||
                        Args.hasArg(OPT_cl_fast_relaxed_math));
   Opts.NoNaNsFPMath = (Args.hasArg(OPT_menable_no_nans) ||
                        Args.hasArg(OPT_cl_unsafe_math_optimizations) ||
                        Args.hasArg(OPT_cl_finite_math_only) ||
                        Args.hasArg(OPT_cl_fast_relaxed_math));
-  Opts.NoSignedZeros = Args.hasArg(OPT_cl_no_signed_zeros);
+  Opts.NoSignedZeros = (Args.hasArg(OPT_cl_no_signed_zeros) ||
+                        Args.hasArg(OPT_fno_signed_zeros));
   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);
   Opts.NoGlobalMerge = Args.hasArg(OPT_mno_global_merge);
   Opts.NoExecStack = Args.hasArg(OPT_mno_exec_stack);
   Opts.FatalWarnings = Args.hasArg(OPT_massembler_fatal_warnings);
   Opts.EnableSegmentedStacks = Args.hasArg(OPT_split_stacks);
   Opts.RelaxAll = Args.hasArg(OPT_mrelax_all);

test/CodeGen/finite-math.c

-// RUN: %clang_cc1 -ffinite-math-only -emit-llvm -o - %s | FileCheck %s
+// RUN: %clang_cc1 -ffinite-math-only -emit-llvm -o - %s | FileCheck %s -check-prefix=CHECK -check-prefix=FINITE
+// RUN: %clang_cc1 -fno-signed-zeros -emit-llvm -o - %s | FileCheck %s -check-prefix=CHECK  -check-prefix=NSZ
+
 float f0, f1, f2;
 
 void foo(void) {
   // CHECK-LABEL: define void @foo()
 
-  // CHECK: fadd nnan ninf
+  // FINITE: fadd nnan ninf
+  // NSZ: fadd nsz
   f0 = f1 + f2;
 
   // CHECK: ret
 }
+

test/Driver/fast-math.c

 // CHECK-NO-FAST-MATH-NO-INFS: "-cc1"
 // CHECK-NO-FAST-MATH-NO-INFS: "-menable-no-infs"
 //
 // RUN: %clang -### -fno-honor-infinities -fno-fast-math -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-INFS-NO-FAST-MATH %s
 // CHECK-NO-INFS-NO-FAST-MATH: "-cc1"
 // CHECK-NO-INFS-NO-FAST-MATH-NOT: "-menable-no-infs"
 //
+// RUN: %clang -### -fno-signed-zeros -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-SIGNED-ZEROS %s
+// CHECK-NO-SIGNED-ZEROS: "-cc1"
+// CHECK-NO-SIGNED-ZEROS: "-fno-signed-zeros"
+//
+// RUN: %clang -### -fno-fast-math -fno-signed-zeros -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-FAST-MATH-NO-SIGNED-ZEROS %s
+// CHECK-NO-FAST-MATH-NO-SIGNED-ZEROS: "-cc1"
+// CHECK-NO-FAST-MATH-NO-SIGNED-ZEROS: "-fno-signed-zeros"
+//
+// RUN: %clang -### -fno-signed-zeros -fno-fast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-SIGNED-ZEROS-NO-FAST-MATH %s
+// CHECK-NO-SIGNED-ZEROS-NO-FAST-MATH: "-cc1"
+// CHECK-NO-SIGNED-ZEROS-NO-FAST-MATH-NOT: "-fno-signed-zeros"
+//
 // RUN: %clang -### -fno-honor-nans -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-NANS %s
 // CHECK-NO-NANS: "-cc1"
 // CHECK-NO-NANS: "-menable-no-nans"
 //
 // RUN: %clang -### -fno-fast-math -fno-honor-nans -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-FAST-MATH-NO-NANS %s
 // CHECK-NO-FAST-MATH-NO-NANS: "-cc1"