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Currently the options ‘ffast-math’ and the option ‘ffp-contract’ are connect.
When ‘ffast-math’ is set, ffp-contract is altered this way:
-ffast-math/ Ofast -> ffp-contract=fast
-fno-fast-math -> if ffp-contract= fast then ffp-contract=on else
ffp-contract unchanged
This differs from gcc which doesn’t connect the two options, and triggered some
spurious warnings; see issue https://github.com/llvm/llvm-project/issues/54625.
The source of the problem is that the ‘ffast-math’ option is an on/off flag,
but the ‘ffp-contract’ is an on/off/fast flag. So when ‘fno-fast-math’ is used
there is no
obvious value for ‘ffp-contract’.
This patch is proposing a change to make the two options unrelated.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D123630
Files:
clang/lib/Driver/ToolChains/Clang.cpp
clang/test/CodeGen/ffp-contract-option.c
clang/test/CodeGen/ffp-model.c
clang/test/Driver/clang_f_opts.c
clang/test/Driver/fast-math.c
Index: clang/test/Driver/fast-math.c
===================================================================
--- clang/test/Driver/fast-math.c
+++ clang/test/Driver/fast-math.c
@@ -78,7 +78,7 @@
// CHECK-FAST-MATH-NO-APPROX-FUNC: "-fno-signed-zeros"
// CHECK-FAST-MATH-NO-APPROX-FUNC: "-mreassociate"
// CHECK-FAST-MATH-NO-APPROX-FUNC: "-freciprocal-math"
-// CHECK-FAST-MATH-NO-APPROX-FUNC: "-ffp-contract=fast"
+// CHECK-FAST-MATH-NO-APPROX-FUNC: "-ffp-contract=on"
// CHECK-FAST-MATH-NO-APPROX-FUNC-NOT: "-ffast-math"
// CHECK-FAST-MATH-NO-APPROX-FUNC-NOT: "-fapprox-func"
//
Index: clang/test/Driver/clang_f_opts.c
===================================================================
--- clang/test/Driver/clang_f_opts.c
+++ clang/test/Driver/clang_f_opts.c
@@ -34,9 +34,10 @@
// DEPRECATED-OFF-CHECK-NOT: -fdeprecated-macro
// RUN: %clang -### -S -ffp-contract=fast %s 2>&1 | FileCheck -check-prefix=FP-CONTRACT-FAST-CHECK %s
-// RUN: %clang -### -S -ffast-math %s 2>&1 | FileCheck -check-prefix=FP-CONTRACT-FAST-CHECK %s
+// RUN: %clang -### -S -ffast-math %s 2>&1 | FileCheck -check-prefix=FP-CONTRACT-ON-CHECK %s
// RUN: %clang -### -S -ffp-contract=off %s 2>&1 | FileCheck -check-prefix=FP-CONTRACT-OFF-CHECK %s
// FP-CONTRACT-FAST-CHECK: -ffp-contract=fast
+// FP-CONTRACT-ON-CHECK: -ffp-contract=on
// FP-CONTRACT-OFF-CHECK: -ffp-contract=off
// RUN: %clang -### -S -funroll-loops %s 2>&1 | FileCheck -check-prefix=CHECK-UNROLL-LOOPS %s
Index: clang/test/CodeGen/ffp-model.c
===================================================================
--- clang/test/CodeGen/ffp-model.c
+++ clang/test/CodeGen/ffp-model.c
@@ -36,13 +36,12 @@
// CHECK-STRICT-FAST: load float, float*
// CHECK-STRICT-FAST: load float, float*
- // CHECK-STRICT-FAST: call fast float @llvm.experimental.constrained.fmul.f32(float {{.*}}, float {{.*}}, {{.*}})
+ // CHECK-STRICT-FAST: call reassoc nnan ninf nsz arcp afn float @llvm.experimental.constrained.fmul.f32(float {{.*}}, float {{.*}}, {{.*}}, {{.*}})
// CHECK-STRICT-FAST: load float, float*
- // CHECK-STRICT-FAST: call fast float @llvm.experimental.constrained.fadd.f32(float {{.*}}, float {{.*}}, {{.*}}
+ // CHECK-STRICT-FAST: call reassoc nnan ninf nsz arcp afn float @llvm.experimental.constrained.fadd.f32(float {{.*}}, float {{.*}}, {{.*}})
// CHECK-FAST1: load float, float*
// CHECK-FAST1: load float, float*
- // CHECK-FAST1: fmul fast float {{.*}}, {{.*}}
- // CHECK-FAST1: load float, float* {{.*}}
- // CHECK-FAST1: fadd fast float {{.*}}, {{.*}}
+ // CHECK-FAST1: load float, float*
+ // CHECK-FAST1: call reassoc nnan ninf nsz arcp afn float @llvm.fmuladd.f32(float {{.*}}, float {{.*}}, float {{.*}})
}
Index: clang/test/CodeGen/ffp-contract-option.c
===================================================================
--- clang/test/CodeGen/ffp-contract-option.c
+++ clang/test/CodeGen/ffp-contract-option.c
@@ -35,7 +35,7 @@
// RUN: | FileCheck %s --check-prefixes=CHECK,CHECK-FPC-ON
// RUN: %clang -Xclang -no-opaque-pointers -S -emit-llvm -ffp-contract=fast -fno-fast-math \
-// RUN: %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-FPC-ON
+// RUN: %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-FPC-FAST
// RUN: %clang -Xclang -no-opaque-pointers -S -emit-llvm -ffp-contract=on -fno-fast-math \
// RUN: %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-FPC-ON
@@ -44,7 +44,7 @@
// RUN: %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-FPC-OFF
// RUN: %clang -Xclang -no-opaque-pointers -S -emit-llvm -ffp-model=fast -fno-fast-math \
-// RUN: %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-FPC-ON
+// RUN: %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-FPC-FAST
// RUN: %clang -Xclang -no-opaque-pointers -S -emit-llvm -ffp-model=precise -fno-fast-math \
// RUN: %s -o - | FileCheck %s --check-prefixes=CHECK,CHECK-FPC-ON
@@ -105,6 +105,12 @@
// CHECK-FPC-ON: load float, float*
// CHECK-FPC-ON: call float @llvm.fmuladd.f32(float {{.*}}, float {{.*}}, float {{.*}})
+ // CHECK-FPC-FAST: load float, float*
+ // CHECK-FPC-FAST: load float, float*
+ // CHECK-FPC-FAST: fmul contract float {{.*}}, {{.*}}
+ // CHECK-FPC-FAST: load float, float*
+ // CHECK-FPC-FAST: fadd contract float {{.*}}, {{.*}}
+
// CHECK-FPC-OFF: load float, float*
// CHECK-FPC-OFF: load float, float*
// CHECK-FPC-OFF: fmul float
Index: clang/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -2990,8 +2990,6 @@
SignedZeros = false;
TrappingMath = false;
RoundingFPMath = 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;
@@ -3010,7 +3008,6 @@
if (!JA.isDeviceOffloading(Action::OFK_Cuda) &&
!JA.isOffloading(Action::OFK_HIP))
if (FPContract == "fast") {
- FPContract = "on";
D.Diag(clang::diag::warn_drv_overriding_flag_option)
<< "-ffp-contract=fast"
<< "-ffp-contract=on";
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