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[LoopVectorize] Fix assertion failure in Fcmp vectorization

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Summary:
When vectorizing fcmps we can trip on incorrect cast assertion when setting the
FastMathFlags after generating the vectorized FCmp.
This can happen if the FCmp can be folded to true or false directly. The fix
here is to set the FastMathFlag using the FastMathFlagBuilder *before* creating
the FCmp Instruction. This is what's done by other optimizations such as
InstCombine.
Added a test case which trips on cast assertion without this patch.

Reviewers: Ayal, mssimpso, mkuper, gilr

Reviewed by: Ayal, mssimpso

Subscribers: llvm-commits, mzolotukhin

Differential Revision: https://reviews.llvm.org/D36244

llvm-svn: 310389
This commit is contained in:
Anna Thomas 2017-08-08 18:07:44 +00:00
parent 3a6ef98b8f
commit ce71877c5e
2 changed files with 28 additions and 1 deletions
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4
lib/Transforms/Vectorize/LoopVectorize.cpp
View File

@ -4863,8 +4863,10 @@ void InnerLoopVectorizer::vectorizeInstruction(Instruction &I) {
Value *B = getOrCreateVectorValue(Cmp->getOperand(1), Part);
Value *C = nullptr;
if (FCmp) {
// Propagate fast math flags.
IRBuilder<>::FastMathFlagGuard FMFG(Builder);
Builder.setFastMathFlags(Cmp->getFastMathFlags());
C = Builder.CreateFCmp(Cmp->getPredicate(), A, B);
cast<FCmpInst>(C)->copyFastMathFlags(Cmp);
} else {
C = Builder.CreateICmp(Cmp->getPredicate(), A, B);
}

25
test/Transforms/LoopVectorize/fcmp-vectorize.ll Normal file
View File

@ -0,0 +1,25 @@
; RUN: opt -loop-vectorize -force-vector-width=4 -force-vector-interleave=1 -S %s | FileCheck %s
; Avoid crashing while trying to vectorize fcmp that can be folded to vector of
; i1 true.
define void @test1() {
; CHECK-LABEL: test1(
; CHECK-LABEL: vector.body:
; CHECK-NEXT: %index = phi i32 [ 0, %vector.ph ], [ %index.next, %vector.body ]
; CHECK-NEXT: %broadcast.splatinsert = insertelement <4 x i32> undef, i32 %index, i32 0
; CHECK: %induction = add <4 x i32> %broadcast.splat, <i32 0, i32 1, i32 2, i32 3>
; CHECK: %index.next = add i32 %index, 4
entry:
br label %loop
loop: ; preds = %loop, %entry
%iv = phi i32 [ 0, %entry ], [ %ivnext, %loop ]
%fcmp = fcmp uno float 0.000000e+00, 0.000000e+00
%ivnext = add nsw i32 %iv, 1
%cnd = icmp sgt i32 %iv, 142
br i1 %cnd, label %exit, label %loop
exit: ; preds = %loop
ret void
}