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[SCCP] Remove manual folding of terminator instructions.

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There are two cases handled here:
1) a branch on undef
2) a switch with an undef condition.

Both cases are currently handled by ResolvedUndefsIn. If we have
a branch on undef, we force its value to false (which is trivially
foldable). If we have a switch on undef, we force to the first
constant (which is also foldable).

llvm-svn: 288725
This commit is contained in:
Davide Italiano 2016-12-05 23:04:21 +00:00
parent a3b8e3dbfd
commit 0faf2ea882
1 changed files with 2 additions and 27 deletions
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29
lib/Transforms/Scalar/SCCP.cpp
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@ -1828,33 +1828,8 @@ static bool runIPSCCP(Module &M, const DataLayout &DL,
// Ignore blockaddress users; BasicBlock's dtor will handle them.
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(ConstantFoldTerminator(I->getParent()) &&
"Terminator should've been folded");
}
// Finally, delete the basic block.