Anastasia created this revision.
Anastasia added reviewers: rjmccall, arsenm.
Herald added subscribers: ebevhan, yaxunl, wdng.
Anastasia marked an inline comment as done.
Anastasia added inline comments.
Anastasia retitled this revision from "[RCF][OpenCL] Set fp contract flag on
-cl-mad-enable" to "[RFC][OpenCL] Set fp contract flag on -cl-mad-enable".
================
Comment at: clang/test/CodeGenOpenCL/relaxed-fpmath.cl:21
+float fused_mad(float a, float b, float c) {
+ // NORMAL: @llvm.fmuladd.f32
+ // FAST: fmul fast float
----------------
I don't find this behavior "NORMAL". I don't believe we should contract
expressions by default in OpenCL...
I think setting `contract` flag on fp instructions with `-cl-mad-enable` should
be sensible considering spec wording:
> -cl-mad-enable Allow a * b + c to be replaced by a mad. The mad computes a *
> b + c with reduced accuracy. For example, some OpenCL devices implement mad
> as truncate the result of a * b before adding it to c
However, I am unclear how it impacts `fdiv` instructions and etc, as I am not
sure how exactly it is optimized. LLVM reference manual says:
> contract
>
> Allow floating-point contraction (e.g. fusing a multiply followed by an
> addition into a fused multiply-and-add).
Presumably `contract` makes no effect in `fdiv`?
Now another question is whether we could remove `LessPreciseFPMAD` from CodeGen
options as I don't feel it has actual uses. Although I might be
misunderstanding this.
TODO: the same applies to `-cl-unsafe-math-optimizations`
https://reviews.llvm.org/D80416
Files:
clang/lib/Frontend/CompilerInvocation.cpp
clang/test/CodeGenOpenCL/relaxed-fpmath.cl
Index: clang/test/CodeGenOpenCL/relaxed-fpmath.cl
===================================================================
--- clang/test/CodeGenOpenCL/relaxed-fpmath.cl
+++ clang/test/CodeGenOpenCL/relaxed-fpmath.cl
@@ -12,10 +12,32 @@
// FAST: fdiv fast float
// FINITE: fdiv nnan ninf float
// UNSAFE: fdiv nnan nsz float
- // MAD: fdiv float
+ // MAD: fdiv contract float
// NOSIGNED: fdiv nsz float
return a / b;
}
+
+float fused_mad(float a, float b, float c) {
+ // NORMAL: @llvm.fmuladd.f32
+ // FAST: fmul fast float
+ // FAST: fadd fast float
+ // MAD: fmul contract float
+ // MAD: fadd contract float
+ return a*b+c;
+}
+
+float fused_mad_accross_stmts(float a, float b, float c) {
+ // NORMAL: fmul float
+ // NORMAL: fadd float
+ // FAST: fmul fast float
+ // FAST: fadd fast float
+ // MAD: fmul contract float
+ // MAD: fadd contract float
+ float t = a*b;
+ return t+c;
+}
+
+
// CHECK: attributes
// NORMAL: "less-precise-fpmad"="false"
Index: clang/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- clang/lib/Frontend/CompilerInvocation.cpp
+++ clang/lib/Frontend/CompilerInvocation.cpp
@@ -2944,7 +2944,7 @@
Opts.NoBitFieldTypeAlign = Args.hasArg(OPT_fno_bitfield_type_align);
Opts.SinglePrecisionConstants =
Args.hasArg(OPT_cl_single_precision_constant);
Opts.FastRelaxedMath = Args.hasArg(OPT_cl_fast_relaxed_math);
- if (Opts.FastRelaxedMath)
+ if (Opts.FastRelaxedMath || Args.hasArg(OPT_cl_mad_enable))
Opts.setDefaultFPContractMode(LangOptions::FPM_Fast);
Opts.HexagonQdsp6Compat = Args.hasArg(OPT_mqdsp6_compat);
Opts.FakeAddressSpaceMap = Args.hasArg(OPT_ffake_address_space_map);
Index: clang/test/CodeGenOpenCL/relaxed-fpmath.cl
===================================================================
--- clang/test/CodeGenOpenCL/relaxed-fpmath.cl
+++ clang/test/CodeGenOpenCL/relaxed-fpmath.cl
@@ -12,10 +12,32 @@
// FAST: fdiv fast float
// FINITE: fdiv nnan ninf float
// UNSAFE: fdiv nnan nsz float
- // MAD: fdiv float
+ // MAD: fdiv contract float
// NOSIGNED: fdiv nsz float
return a / b;
}
+
+float fused_mad(float a, float b, float c) {
+ // NORMAL: @llvm.fmuladd.f32
+ // FAST: fmul fast float
+ // FAST: fadd fast float
+ // MAD: fmul contract float
+ // MAD: fadd contract float
+ return a*b+c;
+}
+
+float fused_mad_accross_stmts(float a, float b, float c) {
+ // NORMAL: fmul float
+ // NORMAL: fadd float
+ // FAST: fmul fast float
+ // FAST: fadd fast float
+ // MAD: fmul contract float
+ // MAD: fadd contract float
+ float t = a*b;
+ return t+c;
+}
+
+
// CHECK: attributes
// NORMAL: "less-precise-fpmad"="false"
Index: clang/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- clang/lib/Frontend/CompilerInvocation.cpp
+++ clang/lib/Frontend/CompilerInvocation.cpp
@@ -2944,7 +2944,7 @@
Opts.NoBitFieldTypeAlign = Args.hasArg(OPT_fno_bitfield_type_align);
Opts.SinglePrecisionConstants = Args.hasArg(OPT_cl_single_precision_constant);
Opts.FastRelaxedMath = Args.hasArg(OPT_cl_fast_relaxed_math);
- if (Opts.FastRelaxedMath)
+ if (Opts.FastRelaxedMath || Args.hasArg(OPT_cl_mad_enable))
Opts.setDefaultFPContractMode(LangOptions::FPM_Fast);
Opts.HexagonQdsp6Compat = Args.hasArg(OPT_mqdsp6_compat);
Opts.FakeAddressSpaceMap = Args.hasArg(OPT_ffake_address_space_map);
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