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[SelectionDAG] Copy FP flags when visiting a binary instruction. 

Summary:
We noticed in Julia that the sequence below no longer turned into
a sequence of FMA instructions in LLVM 7+, but it did in LLVM 6.

```
    %29 = fmul contract <4 x double> %wide.load, %wide.load16
    %30 = fmul contract <4 x double> %wide.load13, %wide.load17
    %31 = fmul contract <4 x double> %wide.load14, %wide.load18
    %32 = fmul contract <4 x double> %wide.load15, %wide.load19
    %33 = fadd fast <4 x double> %vec.phi, %29
    %34 = fadd fast <4 x double> %vec.phi10, %30
    %35 = fadd fast <4 x double> %vec.phi11, %31
    %36 = fadd fast <4 x double> %vec.phi12, %32
```

Unlike Clang, Julia doesn't set the `unsafe-fp-math=true` function
attribute, but rather emits more local instruction flags.

This partially undoes https://reviews.llvm.org/D46854 and if required I can try to minimize the test further.

Reviewers: spatel, mcberg2017

Reviewed By: spatel

Subscribers: chriselrod, merge_guards_bot, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D71495
This commit is contained in:
Valentin Churavy 2019-12-22 14:25:50 -05:00
parent b2c1ba5b1f
commit fb0ccff6e5
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GPG Key ID: 02E09F0CCD46FF9D
2 changed files with 9 additions and 3 deletions
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7
llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
View File

@ -3124,6 +3124,13 @@ void SelectionDAGBuilder::visitBinary(const User &I, unsigned Opcode) {
if (isVectorReductionOp(&I)) {
Flags.setVectorReduction(true);
LLVM_DEBUG(dbgs() << "Detected a reduction operation:" << I << "\n");
// If no flags are set we will propagate the incoming flags, if any flags
// are set, we will intersect them with the incoming flag and so we need to
// copy the FMF flags here.
if (auto *FPOp = dyn_cast<FPMathOperator>(&I)) {
Flags.copyFMF(*FPOp);
}
}
SDValue Op1 = getValue(I.getOperand(0));

5
llvm/test/CodeGen/X86/fmf-reduction.ll
View File

@ -1,14 +1,13 @@
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
; RUN: llc < %s -mtriple=x86_64-- -mattr=fma | FileCheck %s
; FIXME: Propagation of IR FMF should not drop flags when adding the DAG reduction flag.
; Propagation of IR FMF should not drop flags when adding the DAG reduction flag.
; This should include an FMA instruction, not separate FMUL/FADD.
define double @julia_dotf(<4 x double> %x, <4 x double> %y, <4 x double> %z, i1 %t3) {
; CHECK-LABEL: julia_dotf:
; CHECK: # %bb.0:
; CHECK-NEXT: vmulpd %ymm1, %ymm0, %ymm0
; CHECK-NEXT: vaddpd %ymm0, %ymm2, %ymm0
; CHECK-NEXT: vfmadd213pd {{.*#+}} ymm0 = (ymm1 * ymm0) + ymm2
; CHECK-NEXT: vextractf128 $1, %ymm0, %xmm1
; CHECK-NEXT: vaddpd %xmm1, %xmm0, %xmm0
; CHECK-NEXT: vpermilpd {{.*#+}} xmm1 = xmm0[1,0]