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Teach SimplifyCFG to turn

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(indirectbr (select cond, blockaddress(@fn, BlockA),
                            blockaddress(@fn, BlockB)))
into
  (br cond, BlockA, BlockB).


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@120943 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Frits van Bommel
2010-12-05 18:29:03 +00:00
parent 9637d5b22e
commit 7ac40c3ffa
2 changed files with 190 additions and 2 deletions
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lib/Transforms/Utils/SimplifyCFG.cpp
+72 -2
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@@ -374,6 +374,8 @@ static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
} else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
if (BI->isConditional())
Cond = dyn_cast<Instruction>(BI->getCondition());
} else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
Cond = dyn_cast<Instruction>(IBI->getAddress());
}
TI->eraseFromParent();
@@ -1718,6 +1720,71 @@ static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
return true;
}
// SimplifyIndirectBrOnSelect - Replaces
// (indirectbr (select cond, blockaddress(@fn, BlockA),
// blockaddress(@fn, BlockB)))
// with
// (br cond, BlockA, BlockB).
static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
// Check that both operands of the select are block addresses.
BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
if (!TBA || !FBA)
return false;
// Extract the actual blocks.
BasicBlock *TrueBB = TBA->getBasicBlock();
BasicBlock *FalseBB = FBA->getBasicBlock();
// Remove any superfluous successor edges from the CFG.
// First, figure out which successors to preserve.
// If TrueBB and FalseBB are equal, only try to preserve one copy of that
// successor.
BasicBlock *KeepEdge1 = TrueBB;
BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
// Then remove the rest.
for (unsigned I = 0, E = IBI->getNumSuccessors(); I != E; ++I) {
BasicBlock *Succ = IBI->getSuccessor(I);
// Make sure only to keep exactly one copy of each edge.
if (Succ == KeepEdge1)
KeepEdge1 = 0;
else if (Succ == KeepEdge2)
KeepEdge2 = 0;
else
Succ->removePredecessor(IBI->getParent());
}
// Insert an appropriate new terminator.
if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
if (TrueBB == FalseBB)
// We were only looking for one successor, and it was present.
// Create an unconditional branch to it.
BranchInst::Create(TrueBB, IBI);
else
// We found both of the successors we were looking for.
// Create a conditional branch sharing the condition of the select.
BranchInst::Create(TrueBB, FalseBB, SI->getCondition(), IBI);
} else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
// Neither of the selected blocks were successors, so this
// indirectbr must be unreachable.
new UnreachableInst(IBI->getContext(), IBI);
} else {
// One of the selected values was a successor, but the other wasn't.
// Insert an unconditional branch to the one that was found;
// the edge to the one that wasn't must be unreachable.
if (KeepEdge1 == 0)
// Only TrueBB was found.
BranchInst::Create(TrueBB, IBI);
else
// Only FalseBB was found.
BranchInst::Create(FalseBB, IBI);
}
EraseTerminatorInstAndDCECond(IBI);
return true;
}
bool SimplifyCFGOpt::run(BasicBlock *BB) {
bool Changed = false;
Function *Fn = BB->getParent();
@@ -2072,13 +2139,16 @@ bool SimplifyCFGOpt::run(BasicBlock *BB) {
if (IBI->getNumDestinations() == 0) {
// If the indirectbr has no successors, change it to unreachable.
new UnreachableInst(IBI->getContext(), IBI);
IBI->eraseFromParent();
EraseTerminatorInstAndDCECond(IBI);
Changed = true;
} else if (IBI->getNumDestinations() == 1) {
// If the indirectbr has one successor, change it to a direct branch.
BranchInst::Create(IBI->getDestination(0), IBI);
IBI->eraseFromParent();
EraseTerminatorInstAndDCECond(IBI);
Changed = true;
} else if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
if (SimplifyIndirectBrOnSelect(IBI, SI))
return SimplifyCFG(BB) | true;
}
}