Remove redundant option -menable-unsafe-fp-math.

There are currently two options that are used to tell the compiler to perform
unsafe floating-point optimizations:
'-ffast-math' and '-funsafe-math-optimizations'.

'-ffast-math' is enabled by default. It automatically enables the driver option
'-menable-unsafe-fp-math'.
Below is a table illustrating the special operations enabled automatically by
'-ffast-math', '-funsafe-math-optimizations' and '-menable-unsafe-fp-math'
respectively.

Special Operations -ffast-math	-funsafe-math-optimizations -menable-unsafe-fp-math
MathErrno	       0	         1	                    1
FiniteMathOnly         1 	         0                          0
AllowFPReassoc	       1         	 1                          1
NoSignedZero	       1                 1                          1
AllowRecip             1                 1                          1
ApproxFunc             1                 1                          1
RoundingMath	       0                 0                          0
UnsafeFPMath	       1                 0                          1
FPContract	       fast	         on	                    on

'-ffast-math' enables '-fno-math-errno', '-ffinite-math-only',
'-funsafe-math-optimzations' and sets 'FpContract' to 'fast'. The driver option
'-menable-unsafe-fp-math' enables the same special options than
'-funsafe-math-optimizations'. This is redundant.
We propose to remove the driver option '-menable-unsafe-fp-math' and use
instead, the setting of the special operations to set the function attribute
'unsafe-fp-math'. This attribute will be enabled only if those special
operations are enabled and if 'FPContract' is either 'fast' or set to the
default value.

Differential Revision: https://reviews.llvm.org/D135097

Author: zahiraam

clang/docs/ReleaseNotes.rst

@@ -598,6 +598,9 @@ Arm and AArch64 Support in Clang
 
 Floating Point Support in Clang
 -------------------------------
+- The driver option ``-menable-unsafe-fp-math`` has been removed. To enable
+  unsafe floating-point optimizations use ``-funsafe-math-optimizations`` or
+  ``-ffast-math`` instead.
 
 Internal API Changes
 --------------------

clang/include/clang/Driver/Options.td

@@ -1596,10 +1596,6 @@ defm fast_math : BoolFOption<"fast-math",
   PosFlag<SetTrue, [CC1Option], "Allow aggressive, lossy floating-point optimizations",
           [cl_fast_relaxed_math.KeyPath]>,
   NegFlag<SetFalse>>;
-def menable_unsafe_fp_math : Flag<["-"], "menable-unsafe-fp-math">, Flags<[CC1Option]>,
-  HelpText<"Allow unsafe floating-point math optimizations which may decrease precision">,
-  MarshallingInfoFlag<LangOpts<"UnsafeFPMath">>,
-  ImpliedByAnyOf<[cl_unsafe_math_optimizations.KeyPath, ffast_math.KeyPath]>;
 defm math_errno : BoolFOption<"math-errno",
   LangOpts<"MathErrno">, DefaultFalse,
   PosFlag<SetTrue, [CC1Option], "Require math functions to indicate errors by setting errno">,
@@ -1879,20 +1875,23 @@ def fsanitize_undefined_strip_path_components_EQ : Joined<["-"], "fsanitize-unde
 } // end -f[no-]sanitize* flags
 
 def funsafe_math_optimizations : Flag<["-"], "funsafe-math-optimizations">,
-  Group<f_Group>;
+  Group<f_Group>, Flags<[CC1Option]>,
+  HelpText<"Allow unsafe floating-point math optimizations which may decrease precision">,
+  MarshallingInfoFlag<LangOpts<"UnsafeFPMath">>,
+  ImpliedByAnyOf<[cl_unsafe_math_optimizations.KeyPath, ffast_math.KeyPath]>;
 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>;
 defm reciprocal_math : BoolFOption<"reciprocal-math",
   LangOpts<"AllowRecip">, DefaultFalse,
   PosFlag<SetTrue, [CC1Option], "Allow division operations to be reassociated",
-          [menable_unsafe_fp_math.KeyPath]>,
+          [funsafe_math_optimizations.KeyPath]>,
   NegFlag<SetFalse>>;
 defm approx_func : BoolFOption<"approx-func", LangOpts<"ApproxFunc">, DefaultFalse,
    PosFlag<SetTrue, [CC1Option], "Allow certain math function calls to be replaced "
            "with an approximately equivalent calculation",
-           [menable_unsafe_fp_math.KeyPath]>,
+           [funsafe_math_optimizations.KeyPath]>,
    NegFlag<SetFalse>>;
 defm finite_math_only : BoolFOption<"finite-math-only",
   LangOpts<"FiniteMathOnly">, DefaultFalse,
@@ -1901,7 +1900,7 @@ defm finite_math_only : BoolFOption<"finite-math-only",
 defm signed_zeros : BoolFOption<"signed-zeros",
   LangOpts<"NoSignedZero">, DefaultFalse,
   NegFlag<SetTrue, [CC1Option], "Allow optimizations that ignore the sign of floating point zeros",
-            [cl_no_signed_zeros.KeyPath, menable_unsafe_fp_math.KeyPath]>,
+            [cl_no_signed_zeros.KeyPath, funsafe_math_optimizations.KeyPath]>,
   PosFlag<SetFalse>>;
 def fhonor_nans : Flag<["-"], "fhonor-nans">, Group<f_Group>;
 def fno_honor_nans : Flag<["-"], "fno-honor-nans">, Group<f_Group>;
@@ -5426,7 +5425,7 @@ def menable_no_nans : Flag<["-"], "menable-no-nans">,
   MarshallingInfoFlag<LangOpts<"NoHonorNaNs">>, ImpliedByAnyOf<[ffinite_math_only.KeyPath]>;
 def mreassociate : Flag<["-"], "mreassociate">,
   HelpText<"Allow reassociation transformations for floating-point instructions">,
-  MarshallingInfoFlag<LangOpts<"AllowFPReassoc">>, ImpliedByAnyOf<[menable_unsafe_fp_math.KeyPath]>;
+  MarshallingInfoFlag<LangOpts<"AllowFPReassoc">>, ImpliedByAnyOf<[funsafe_math_optimizations.KeyPath]>;
 def mabi_EQ_ieeelongdouble : Flag<["-"], "mabi=ieeelongdouble">,
   HelpText<"Use IEEE 754 quadruple-precision for long double">,
   MarshallingInfoFlag<LangOpts<"PPCIEEELongDouble">>;

clang/lib/CodeGen/CGCall.cpp

@@ -1862,7 +1862,11 @@ void CodeGenModule::getDefaultFunctionAttributes(StringRef Name,
       FuncAttrs.addAttribute("no-nans-fp-math", "true");
     if (LangOpts.ApproxFunc)
       FuncAttrs.addAttribute("approx-func-fp-math", "true");
-    if (LangOpts.UnsafeFPMath)
+    if ((LangOpts.FastMath ||
+         !LangOpts.FastMath && LangOpts.AllowFPReassoc && LangOpts.AllowRecip &&
+             !LangOpts.FiniteMathOnly && LangOpts.NoSignedZero &&
+             LangOpts.ApproxFunc) &&
+        LangOpts.getDefaultFPContractMode() != LangOptions::FPModeKind::FPM_Off)
       FuncAttrs.addAttribute("unsafe-fp-math", "true");
     if (CodeGenOpts.SoftFloat)
       FuncAttrs.addAttribute("use-soft-float", "true");

clang/lib/Driver/ToolChains/Clang.cpp

@@ -3103,7 +3103,7 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
 
   if (!MathErrno && AssociativeMath && ReciprocalMath && !SignedZeros &&
       ApproxFunc && !TrappingMath)
-    CmdArgs.push_back("-menable-unsafe-fp-math");
+    CmdArgs.push_back("-funsafe-math-optimizations");
 
   if (!SignedZeros)
     CmdArgs.push_back("-fno-signed-zeros");

clang/test/CodeGen/fp-options-to-fast-math-flags.c

@@ -5,7 +5,7 @@
 // RUN: %clang_cc1 -triple x86_64-unknown-unknown -fno-signed-zeros -emit-llvm -o - %s | FileCheck -check-prefix CHECK-NO-SIGNED-ZEROS %s
 // RUN: %clang_cc1 -triple x86_64-unknown-unknown -mreassociate -emit-llvm -o - %s | FileCheck -check-prefix CHECK-REASSOC %s
 // RUN: %clang_cc1 -triple x86_64-unknown-unknown -freciprocal-math -emit-llvm -o - %s | FileCheck -check-prefix CHECK-RECIP %s
-// RUN: %clang_cc1 -triple x86_64-unknown-unknown -menable-unsafe-fp-math -emit-llvm -o - %s | FileCheck -check-prefix CHECK-UNSAFE %s
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown -funsafe-math-optimizations -emit-llvm -o - %s | FileCheck -check-prefix CHECK-UNSAFE %s
 // RUN: %clang_cc1 -triple x86_64-unknown-unknown -ffast-math -emit-llvm -o - %s | FileCheck -check-prefix CHECK-FAST %s
 
 float fn(float);

clang/test/CodeGen/func-attr.c

@@ -0,0 +1,12 @@
+// RUN: %clang -c -ffast-math -emit-llvm -S -o - %s \
+// RUN: | FileCheck %s
+
+// RUN: %clang -c -funsafe-math-optimizations -emit-llvm -S -o - %s \
+// RUN: | FileCheck %s
+
+float foo(float a, float b) {
+  return a+b;
+}
+
+// CHECK: define{{.*}} float @foo(float noundef %a, float noundef %b) [[FAST_ATTRS:#[0-9]+]]
+// CHECK: attributes [[FAST_ATTRS]] = { {{.*}} "approx-func-fp-math"="true" {{.*}} "no-signed-zeros-fp-math"="true" "no-trapping-math"="true" {{.*}} "unsafe-fp-math"="true"

clang/test/CodeGen/libcalls.c

@@ -1,6 +1,6 @@
 // RUN: %clang_cc1 -Wno-implicit-function-declaration -fmath-errno -emit-llvm -o - %s -triple i386-unknown-unknown | FileCheck -check-prefix CHECK-YES %s
 // RUN: %clang_cc1 -Wno-implicit-function-declaration -emit-llvm -o - %s -triple i386-unknown-unknown | FileCheck -check-prefix CHECK-NO %s
-// RUN: %clang_cc1 -Wno-implicit-function-declaration -menable-unsafe-fp-math -emit-llvm -o - %s -triple i386-unknown-unknown | FileCheck -check-prefix CHECK-FAST %s
+// RUN: %clang_cc1 -Wno-implicit-function-declaration -funsafe-math-optimizations -emit-llvm -o - %s -triple i386-unknown-unknown | FileCheck -check-prefix CHECK-FAST %s
 
 // CHECK-YES-LABEL: define{{.*}} void @test_sqrt
 // CHECK-NO-LABEL: define{{.*}} void @test_sqrt

clang/test/CodeGenCUDA/propagate-metadata.cu

@@ -22,7 +22,7 @@
 
 // RUN: %clang_cc1 -x cuda %s -emit-llvm -mlink-builtin-bitcode %t.bc \
 // RUN:   -fdenormal-fp-math-f32=preserve-sign -o - \
-// RUN:   -fcuda-is-device -menable-unsafe-fp-math -triple nvptx-unknown-unknown \
+// RUN:   -fcuda-is-device -funsafe-math-optimizations -triple nvptx-unknown-unknown \
 // RUN: | FileCheck %s --check-prefix=CHECK --check-prefix=FAST
 
 // Wrap everything in extern "C" so we don't have to worry about name mangling

clang/test/Driver/cl-options.c

@@ -43,23 +43,23 @@
 // EXTERNAL_I: "-isystem" "path"
 
 // RUN: %clang_cl /fp:fast /fp:except -### -- %s 2>&1 | FileCheck -check-prefix=fpexcept %s
-// fpexcept-NOT: -menable-unsafe-fp-math
+// fpexcept-NOT: -funsafe-math-optimizations
 // fpexcept: -ffp-exception-behavior=strict
 
 // RUN: %clang_cl /fp:fast /fp:except /fp:except- -### -- %s 2>&1 | FileCheck -check-prefix=fpexcept_ %s
-// fpexcept_: -menable-unsafe-fp-math
+// fpexcept_: -funsafe-math-optimizations
 // fpexcept_: -ffp-exception-behavior=ignore
 
 // RUN: %clang_cl /fp:precise /fp:fast -### -- %s 2>&1 | FileCheck -check-prefix=fpfast %s
-// fpfast: -menable-unsafe-fp-math
+// fpfast: -funsafe-math-optimizations
 // fpfast: -ffast-math
 
 // RUN: %clang_cl /fp:fast /fp:precise -### -- %s 2>&1 | FileCheck -check-prefix=fpprecise %s
-// fpprecise-NOT: -menable-unsafe-fp-math
+// fpprecise-NOT: -funsafe-math-optimizations
 // fpprecise-NOT: -ffast-math
 
 // RUN: %clang_cl /fp:fast /fp:strict -### -- %s 2>&1 | FileCheck -check-prefix=fpstrict %s
-// fpstrict-NOT: -menable-unsafe-fp-math
+// fpstrict-NOT: -funsafe-math-optimizations
 // fpstrict-NOT: -ffast-math
 // fpstrict: -ffp-contract=off
 

clang/test/Driver/fast-math.c

@@ -151,14 +151,14 @@
 // RUN:     -fno-signed-zeros -fno-trapping-math -fapprox-func -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-UNSAFE-MATH %s
 // CHECK-UNSAFE-MATH: "-cc1"
-// CHECK-UNSAFE-MATH: "-menable-unsafe-fp-math"
+// CHECK-UNSAFE-MATH: "-funsafe-math-optimizations"
 // CHECK-UNSAFE-MATH: "-mreassociate"
 //
 // RUN: %clang -### -fno-fast-math -fno-math-errno -fassociative-math -freciprocal-math \
 // RUN:     -fno-signed-zeros -fno-trapping-math -fapprox-func -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NO-FAST-MATH-UNSAFE-MATH %s
 // CHECK-NO-FAST-MATH-UNSAFE-MATH: "-cc1"
-// CHECK-NO-FAST-MATH-UNSAFE-MATH: "-menable-unsafe-fp-math"
+// CHECK-NO-FAST-MATH-UNSAFE-MATH: "-funsafe-math-optimizations"
 // CHECK-NO-FAST-MATH-UNSAFE-MATH: "-mreassociate"
 
 // The 2nd -fno-fast-math overrides -fassociative-math.
@@ -167,7 +167,7 @@
 // RUN:     -fno-fast-math -fno-signed-zeros -fno-trapping-math -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-UNSAFE-MATH-NO-FAST-MATH %s
 // CHECK-UNSAFE-MATH-NO-FAST-MATH: "-cc1"
-// CHECK-UNSAFE-MATH-NO-FAST-MATH-NOT: "-menable-unsafe-fp-math"
+// CHECK-UNSAFE-MATH-NO-FAST-MATH-NOT: "-funsafe-math-optimizations"
 // CHECK-UNSAFE-MATH-NO-FAST-MATH-NOT: "-mreassociate"
 //
 // Check that various umbrella flags also enable these frontend options.
@@ -280,7 +280,7 @@
 // RUN:   | FileCheck --check-prefix=CHECK-NO-UNSAFE-MATH %s
 
 // CHECK-NO-UNSAFE-MATH: "-cc1"
-// CHECK-NO-UNSAFE-MATH-NOT: "-menable-unsafe-fp-math"
+// CHECK-NO-UNSAFE-MATH-NOT: "-funsafe-math-optimizations"
 // CHECK-NO_UNSAFE-MATH-NOT: "-mreassociate"
 // CHECK-NO-UNSAFE-MATH: "-o"
 
@@ -292,9 +292,9 @@
 // RUN:   | FileCheck --check-prefix=CHECK-REASSOC-NO-UNSAFE-MATH %s
 
 // CHECK-REASSOC-NO-UNSAFE-MATH: "-cc1"
-// CHECK-REASSOC-NO-UNSAFE-MATH-NOT: "-menable-unsafe-fp-math"
+// CHECK-REASSOC-NO_UNSAFE-MATH-NOT: "-funsafe-math-optimizations"
 // CHECK-REASSOC-NO_UNSAFE-MATH: "-mreassociate"
-// CHECK-REASSOC-NO-UNSAFE-MATH-NOT: "-menable-unsafe-fp-math"
+// CHECK-REASSOC-NO-UNSAFE-MATH-NOT: "-funsafe-math-optimizations"
 // CHECK-REASSOC-NO-UNSAFE-MATH: "-o"
 
 
@@ -309,9 +309,9 @@
 // RUN:   | FileCheck --check-prefix=CHECK-NO-REASSOC-NO-UNSAFE-MATH %s
 
 // CHECK-NO-REASSOC-NO-UNSAFE-MATH: "-cc1"
-// CHECK-NO-REASSOC-NO-UNSAFE-MATH-NOT: "-menable-unsafe-fp-math"
+// CHECK-NO-REASSOC-NO_UNSAFE-MATH-NOT: "-funsafe-math-optimizations"
 // CHECK-NO-REASSOC-NO_UNSAFE-MATH-NOT: "-mreassociate"
-// CHECK-NO-REASSOC-NO-UNSAFE-MATH-NOT: "-menable-unsafe-fp-math"
+// CHECK-NO-REASSOC-NO_UNSAFE-MATH-NOT: "-funsafe-math-optimizations"
 // CHECK-NO-REASSOC-NO-UNSAFE-MATH: "-o"