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[SLP] avoid unreachable code crash/infloop

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Example based on the post-commit comments for D88735.
This commit is contained in:
Sanjay Patel 2020-11-17 15:09:06 -05:00
parent 8e1729917d
commit 1cf013898b
2 changed files with 39 additions and 2 deletions
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6
lib/Transforms/Vectorize/SLPVectorizer.cpp
View File

@ -7686,10 +7686,12 @@ bool SLPVectorizerPass::vectorizeChainsInBlock(BasicBlock *BB, BoUpSLP &R) {
// Try to vectorize the incoming values of the PHI, to catch reductions
// that feed into PHIs.
for (unsigned I = 0, E = P->getNumIncomingValues(); I != E; I++) {
// Skip if the incoming block is the current BB for now.
// Skip if the incoming block is the current BB for now. Also, bypass
// unreachable IR for efficiency and to avoid crashing.
// TODO: Collect the skipped incoming values and try to vectorize them
// after processing BB.
if (BB == P->getIncomingBlock(I))
if (BB == P->getIncomingBlock(I) ||
!DT->isReachableFromEntry(P->getIncomingBlock(I)))
continue;
Changed |= vectorizeRootInstruction(nullptr, P->getIncomingValue(I),

35
test/Transforms/SLPVectorizer/X86/horizontal.ll
View File

@ -1731,4 +1731,39 @@ exit:
ret i32 %sum.1
}
; Make sure we do not crash or infinite loop on ill-formed IR.
define void @unreachable_block() {
; CHECK-LABEL: @unreachable_block(
; CHECK-NEXT: bb.0:
; CHECK-NEXT: br label [[BB_1:%.*]]
; CHECK: dead:
; CHECK-NEXT: [[T0:%.*]] = add i16 [[T0]], undef
; CHECK-NEXT: br label [[BB_1]]
; CHECK: bb.1:
; CHECK-NEXT: [[T1:%.*]] = phi i16 [ undef, [[BB_0:%.*]] ], [ [[T0]], [[DEAD:%.*]] ]
; CHECK-NEXT: ret void
;
; STORE-LABEL: @unreachable_block(
; STORE-NEXT: bb.0:
; STORE-NEXT: br label [[BB_1:%.*]]
; STORE: dead:
; STORE-NEXT: [[T0:%.*]] = add i16 [[T0]], undef
; STORE-NEXT: br label [[BB_1]]
; STORE: bb.1:
; STORE-NEXT: [[T1:%.*]] = phi i16 [ undef, [[BB_0:%.*]] ], [ [[T0]], [[DEAD:%.*]] ]
; STORE-NEXT: ret void
;
bb.0:
br label %bb.1
dead:
%t0 = add i16 %t0, undef ; unreachable IR may depend on itself
br label %bb.1
bb.1:
%t1 = phi i16 [ undef, %bb.0 ], [ %t0, %dead ]
ret void
}
declare i32 @__gxx_personality_v0(...)