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[GuardWidening] Ignore guards with trivial conditions

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Guard widening should not spend efforts on dealing with guards with trivial true/false conditions.
Such guards can easily be eliminated by any further cleanup pass like instcombine. However we
should not unconditionally delete them because it may be profitable to widen other conditions
into such guards.

Differential Revision: https://reviews.llvm.org/D50247
Reviewed By: fedor.sergeev

llvm-svn: 340381
This commit is contained in:
Max Kazantsev 2018-08-22 02:40:49 +00:00
parent 8c95eeae9d
commit c8eea01630
2 changed files with 32 additions and 0 deletions
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6
lib/Transforms/Scalar/GuardWidening.cpp
View File

@ -347,6 +347,12 @@ bool GuardWideningImpl::eliminateGuardViaWidening(
Instruction *GuardInst, const df_iterator<DomTreeNode *> &DFSI,
const DenseMap<BasicBlock *, SmallVector<Instruction *, 8>> &
GuardsInBlock, bool InvertCondition) {
// Ignore trivial true or false conditions. These instructions will be
// trivially eliminated by any cleanup pass. Do not erase them because other
// guards can possibly be widened into them.
if (isa<ConstantInt>(getCondition(GuardInst)))
return false;
Instruction *BestSoFar = nullptr;
auto BestScoreSoFar = WS_IllegalOrNegative;
auto *GuardInstLoop = LI.getLoopFor(GuardInst->getParent());

26
test/Transforms/GuardWidening/basic.ll
View File

@ -379,3 +379,29 @@ left:
right:
ret void
}
; Make sure we do not widen guard by trivial true conditions into something.
define void @f_15(i1 %cond_0, i1 %cond_1) {
; CHECK-LABEL: @f_15(
entry:
; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 %cond_0) [ "deopt"() ]
; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ]
; CHECK: ret void
call void(i1, ...) @llvm.experimental.guard(i1 %cond_0) [ "deopt"() ]
call void(i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ]
ret void
}
; Make sure we do not widen guard by trivial false conditions into something.
define void @f_16(i1 %cond_0, i1 %cond_1) {
; CHECK-LABEL: @f_16(
entry:
; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 %cond_0) [ "deopt"() ]
; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 false) [ "deopt"() ]
; CHECK: ret void
call void(i1, ...) @llvm.experimental.guard(i1 %cond_0) [ "deopt"() ]
call void(i1, ...) @llvm.experimental.guard(i1 false) [ "deopt"() ]
ret void
}