Anastasia created this revision.
Anastasia added reviewers: rjmccall, arsenm.
Herald added subscribers: ebevhan, yaxunl, wdng.
Currently, clang will generate fused operation `fmuladd` for expressions like
`a*b+c`. However, I can't find anything in the spec that explains this
behavior. But clang was doing this for almost 10 years....
I looked at:
**s6.13.2 **where it details fp conract pragma:
// on-off-switch is one of ON, OFF, or DEFAULT.
// The DEFAULT value is ON.
#pragma OPENCL FP_CONTRACT on-off-switch
The default behavior here refers to the default value of the pragma when used
in the source code.
**s7.4** table 38
x * y + z
Implemented either as a correctly rounded fma or as a multiply and an add
both of which are correctly rounded.
This table described behavior when `-cl-unsafe-math-optimizations` flag is
passed.
I can't find anything else that would justify allowing fused operations,
therefore I assume this is not safe to do and can cause issues on some
applications/targets
https://reviews.llvm.org/D80440
Files:
clang/lib/Frontend/CompilerInvocation.cpp
clang/test/CodeGenOpenCL/relaxed-fpmath.cl
clang/test/CodeGenOpenCL/single-precision-constant.cl
Index: clang/test/CodeGenOpenCL/single-precision-constant.cl
===================================================================
--- clang/test/CodeGenOpenCL/single-precision-constant.cl
+++ clang/test/CodeGenOpenCL/single-precision-constant.cl
@@ -1,6 +1,7 @@
// RUN: %clang_cc1 %s -cl-single-precision-constant -emit-llvm -o - |
FileCheck %s
float fn(float f) {
- // CHECK: tail call float @llvm.fmuladd.f32(float %f, float 2.000000e+00,
float 1.000000e+00)
+ // CHECK: fmul float %f, 2.000000e+00
+ // CHECK: fadd float %mul, 1.000000e+00
return f*2. + 1.;
}
Index: clang/test/CodeGenOpenCL/relaxed-fpmath.cl
===================================================================
--- clang/test/CodeGenOpenCL/relaxed-fpmath.cl
+++ clang/test/CodeGenOpenCL/relaxed-fpmath.cl
@@ -17,7 +17,8 @@
}
float fused_mad(float a, float b, float c) {
- // NORMAL: tail call float @llvm.fmuladd.f32(float %a, float %b, float %c)
+ // NORMAL: fmul float
+ // NORMAL: fadd float
// FAST: fmul fast float
// FAST: fadd fast float
// MAD: fmul contract float
Index: clang/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- clang/lib/Frontend/CompilerInvocation.cpp
+++ clang/lib/Frontend/CompilerInvocation.cpp
@@ -2322,7 +2322,6 @@
Opts.AltiVec = 0;
Opts.ZVector = 0;
Opts.setLaxVectorConversions(LangOptions::LaxVectorConversionKind::None);
- Opts.setDefaultFPContractMode(LangOptions::FPM_On);
Opts.NativeHalfType = 1;
Opts.NativeHalfArgsAndReturns = 1;
Opts.OpenCLCPlusPlus = Opts.CPlusPlus;
Index: clang/test/CodeGenOpenCL/single-precision-constant.cl
===================================================================
--- clang/test/CodeGenOpenCL/single-precision-constant.cl
+++ clang/test/CodeGenOpenCL/single-precision-constant.cl
@@ -1,6 +1,7 @@
// RUN: %clang_cc1 %s -cl-single-precision-constant -emit-llvm -o - | FileCheck %s
float fn(float f) {
- // CHECK: tail call float @llvm.fmuladd.f32(float %f, float 2.000000e+00, float 1.000000e+00)
+ // CHECK: fmul float %f, 2.000000e+00
+ // CHECK: fadd float %mul, 1.000000e+00
return f*2. + 1.;
}
Index: clang/test/CodeGenOpenCL/relaxed-fpmath.cl
===================================================================
--- clang/test/CodeGenOpenCL/relaxed-fpmath.cl
+++ clang/test/CodeGenOpenCL/relaxed-fpmath.cl
@@ -17,7 +17,8 @@
}
float fused_mad(float a, float b, float c) {
- // NORMAL: tail call float @llvm.fmuladd.f32(float %a, float %b, float %c)
+ // NORMAL: fmul float
+ // NORMAL: fadd float
// FAST: fmul fast float
// FAST: fadd fast float
// MAD: fmul contract float
Index: clang/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- clang/lib/Frontend/CompilerInvocation.cpp
+++ clang/lib/Frontend/CompilerInvocation.cpp
@@ -2322,7 +2322,6 @@
Opts.AltiVec = 0;
Opts.ZVector = 0;
Opts.setLaxVectorConversions(LangOptions::LaxVectorConversionKind::None);
- Opts.setDefaultFPContractMode(LangOptions::FPM_On);
Opts.NativeHalfType = 1;
Opts.NativeHalfArgsAndReturns = 1;
Opts.OpenCLCPlusPlus = Opts.CPlusPlus;
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