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[SCCP] Remove manual folding of terminator instructions.

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Summary:
BranchInst, SwitchInst (with non-default case) with Undef as input is not
possible at this point. As we always default-fold terminator to one target in
ResolvedUndefsIn and set the input accordingly.

So we should only have constantint/blockaddress here.

If ConstantFoldTerminator fails, that could mean 2 things.

1. ConstantFoldTerminator is doing something unexpected, i.e. not folding on constantint
or blockaddress and not making blocks that should be dead dead.
2. This is not a terminator on constantint or blockaddress. Its on a constant or
overdefined, then this block should not be dead.

In both cases, we should assert.

Reviewers: davide, efriedma, sanjoy

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D30381

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@296281 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Xin Tong 2017-02-26 02:11:24 +00:00
parent a11dc45cbd
commit 650a66fb4c
1 changed files with 3 additions and 26 deletions
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29
lib/Transforms/Scalar/SCCP.cpp
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@ -1824,32 +1824,9 @@ static bool runIPSCCP(Module &M, const DataLayout &DL,
if (!I) continue;
bool Folded = ConstantFoldTerminator(I->getParent());
if (!Folded) {
// The constant folder may not have been able to fold the terminator
// if this is a branch or switch on undef. Fold it manually as a
// branch to the first successor.
#ifndef NDEBUG
if (auto *BI = dyn_cast<BranchInst>(I)) {
assert(BI->isConditional() && isa<UndefValue>(BI->getCondition()) &&
"Branch should be foldable!");
} else if (auto *SI = dyn_cast<SwitchInst>(I)) {
assert(isa<UndefValue>(SI->getCondition()) && "Switch should fold");
} else {
llvm_unreachable("Didn't fold away reference to block!");
}
#endif
// Make this an uncond branch to the first successor.
TerminatorInst *TI = I->getParent()->getTerminator();
BranchInst::Create(TI->getSuccessor(0), TI);
// Remove entries in successor phi nodes to remove edges.
for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i)
TI->getSuccessor(i)->removePredecessor(TI->getParent());
// Remove the old terminator.
TI->eraseFromParent();
}
assert(Folded &&
"Expect TermInst on constantint or blockaddress to be folded");
(void) Folded;
}
// Finally, delete the basic block.