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[JumpThread] Do RAUW in case Cond folds to a constant in the CFG

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Summary: [JumpThread] Do RAUW in case Cond folds to a constant in the CFG

Reviewers: sanjoy

Reviewed By: sanjoy

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D32407

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301804 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Xin Tong 2017-05-01 15:34:17 +00:00
parent 195d3fa988
commit fc533c3fb3
2 changed files with 81 additions and 8 deletions
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32
lib/Transforms/Scalar/JumpThreading.cpp
View File

@ -1250,6 +1250,8 @@ bool JumpThreadingPass::ProcessThreadableEdges(Value *Cond, BasicBlock *BB,
BasicBlock *OnlyDest = nullptr;
BasicBlock *MultipleDestSentinel = (BasicBlock*)(intptr_t)~0ULL;
Constant *OnlyVal = nullptr;
Constant *MultipleVal = (Constant *)(intptr_t)~0ULL;
for (const auto &PredValue : PredValues) {
BasicBlock *Pred = PredValue.second;
@ -1277,10 +1279,17 @@ bool JumpThreadingPass::ProcessThreadableEdges(Value *Cond, BasicBlock *BB,
}
// If we have exactly one destination, remember it for efficiency below.
if (PredToDestList.empty())
if (PredToDestList.empty()) {
OnlyDest = DestBB;
else if (OnlyDest != DestBB)
OnlyDest = MultipleDestSentinel;
OnlyVal = Val;
} else {
if (OnlyDest != DestBB)
OnlyDest = MultipleDestSentinel;
// It possible we have same destination, but different value, e.g. default
// case in switchinst.
if (Val != OnlyVal)
OnlyVal = MultipleVal;
}
PredToDestList.push_back(std::make_pair(Pred, DestBB));
}
@ -1310,11 +1319,18 @@ bool JumpThreadingPass::ProcessThreadableEdges(Value *Cond, BasicBlock *BB,
// If the condition is now dead due to the removal of the old terminator,
// erase it.
auto *CondInst = dyn_cast<Instruction>(Cond);
if (CondInst && CondInst->use_empty())
CondInst->eraseFromParent();
// FIXME: in case this instruction is defined in the current BB and it
// resolves to a single value from all predecessors, we can do RAUW.
if (auto *CondInst = dyn_cast<Instruction>(Cond)) {
if (CondInst->use_empty() && !CondInst->mayHaveSideEffects())
CondInst->eraseFromParent();
else if (OnlyVal && OnlyVal != MultipleVal &&
CondInst->getParent() == BB) {
// If we just learned Cond is the same value for all uses of the
// condition, replace it with a constant value
CondInst->replaceAllUsesWith(OnlyVal);
if (!CondInst->mayHaveSideEffects())
CondInst->eraseFromParent();
}
}
return true;
}
}

57
test/Transforms/JumpThreading/fold-not-thread.ll
View File

@ -133,3 +133,60 @@ L3:
ret void
}
; Make sure we can do the RAUW for %add...
;
; CHECK-LABEL: @rauw_if_possible(
; CHECK: call void @f4(i32 96)
define void @rauw_if_possible(i32 %value) nounwind {
entry:
%cmp = icmp eq i32 %value, 32
br i1 %cmp, label %L0, label %L3
L0:
call i32 @f2()
call i32 @f2()
%add = add i32 %value, 64
switch i32 %add, label %L3 [
i32 32, label %L1
i32 96, label %L2
]
L1:
call void @f3()
ret void
L2:
call void @f4(i32 %add)
ret void
L3:
call void @f3()
ret void
}
; Make sure we can NOT do the RAUW for %add...
;
; CHECK-LABEL: @rauw_if_possible2(
; CHECK: call void @f4(i32 %add)
define void @rauw_if_possible2(i32 %value) nounwind {
entry:
%cmp = icmp eq i32 %value, 32
%add = add i32 %value, 64
br i1 %cmp, label %L0, label %L2
L0:
call i32 @f2()
call i32 @f2()
switch i32 %add, label %L3 [
i32 32, label %L1
i32 96, label %L2
]
L1:
call void @f3()
ret void
L2:
call void @f4(i32 %add)
ret void
L3:
call void @f3()
ret void
}