Process the -freciprocal-math optimization flag (PR20912)

rotateright · rotateright · commit 359b105745cc · 2015-04-09T15:03:23.000Z
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
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
@@ -561,7 +561,9 @@ 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 freciprocal_math :
+  Flag<["-"], "freciprocal-math">, Group<f_Group>, Flags<[CC1Option]>,
+  HelpText<"Allow division operations to be reassociated">;
 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>;
diff --git a/clang/include/clang/Frontend/CodeGenOptions.def b/clang/include/clang/Frontend/CodeGenOptions.def
@@ -81,7 +81,8 @@ CODEGENOPT(NoGlobalMerge     , 1, 0) ///< Set when -mno-global-merge is enabled.
 CODEGENOPT(NoImplicitFloat   , 1, 0) ///< Set when -mno-implicit-float is enabled.
 CODEGENOPT(NoInfsFPMath      , 1, 0) ///< Assume FP arguments, results not +-Inf.
 CODEGENOPT(NoSignedZeros     , 1, 0) ///< Allow ignoring the signedness of FP zero
-CODEGENOPT(NoInline          , 1, 0) ///< Set when -fno-inline is enabled. 
+CODEGENOPT(ReciprocalMath    , 1, 0) ///< Allow FP divisions to be reassociated.
+CODEGENOPT(NoInline          , 1, 0) ///< Set when -fno-inline is enabled.
                                      ///< Disables use of the inline keyword.
 CODEGENOPT(NoNaNsFPMath      , 1, 0) ///< Assume FP arguments, results not NaN.
 CODEGENOPT(NoZeroInitializedInBSS , 1, 0) ///< -fno-zero-initialized-in-bss.
diff --git 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
@@ -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
@@ -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);
diff --git a/clang/test/CodeGen/finite-math.c b/clang/test/CodeGen/finite-math.c
@@ -1,5 +1,6 @@
 // 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
+// RUN: %clang_cc1 -freciprocal-math -emit-llvm -o - %s | FileCheck %s -check-prefix=CHECK  -check-prefix=RECIP
 
 float f0, f1, f2;
 
@@ -8,6 +9,7 @@ void foo(void) {
 
   // FINITE: fadd nnan ninf
   // NSZ: fadd nsz
+  // RECIP: fadd arcp
   f0 = f1 + f2;
 
   // CHECK: ret
diff --git a/clang/test/Driver/fast-math.c b/clang/test/Driver/fast-math.c
@@ -40,6 +40,21 @@
 // CHECK-NO-SIGNED-ZEROS-NO-FAST-MATH: "-cc1"
 // CHECK-NO-SIGNED-ZEROS-NO-FAST-MATH-NOT: "-fno-signed-zeros"
 //
+// RUN: %clang -### -freciprocal-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-RECIPROCAL-MATH %s
+// CHECK-RECIPROCAL-MATH: "-cc1"
+// CHECK-RECIPROCAL-MATH: "-freciprocal-math"
+//
+// RUN: %clang -### -fno-fast-math -freciprocal-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-FAST-MATH-RECIPROCAL-MATH %s
+// CHECK-NO-FAST-MATH-RECIPROCAL-MATH: "-cc1"
+// CHECK-NO-FAST-MATH-RECIPROCAL-MATH: "-freciprocal-math"
+//
+// RUN: %clang -### -freciprocal-math -fno-fast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-RECIPROCAL-MATH-NO-FAST-MATH %s
+// CHECK-RECIPROCAL-MATH-NO-FAST-MATH: "-cc1"
+// CHECK-RECIPROCAL-MATH-NO-FAST-MATH-NOT: "-freciprocal-math"
+//
 // RUN: %clang -### -fno-honor-nans -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-NANS %s
 // CHECK-NO-NANS: "-cc1"

Original file line number	Diff line number	Diff line change
`@@ -70,6 +70,9 @@ CodeGenFunction::CodeGenFunction(CodeGenModule &cgm, bool suppressNewContext)`
`70`	`70`	`if (CGM.getCodeGenOpts().NoSignedZeros) {`
`71`	`71`	`FMF.setNoSignedZeros();`
`72`	`72`	`}`
	`73`	`+ if (CGM.getCodeGenOpts().ReciprocalMath) {`
	`74`	`+ FMF.setAllowReciprocal();`
	`75`	`+ }`
`73`	`76`	`Builder.SetFastMathFlags(FMF);`
`74`	`77`	`}`
`75`	`78`