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pull a bunch of logic out of SimplifyCFG into a helper fn
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@23407 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
parent
7c439929bc
commit
f58c1a578e
@ -1018,6 +1018,116 @@ static bool FoldCondBranchOnPHI(BranchInst *BI) {
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return false;
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return false;
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}
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}
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/// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
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/// PHI node, see if we can eliminate it.
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static bool FoldTwoEntryPHINode(PHINode *PN) {
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// Ok, this is a two entry PHI node. Check to see if this is a simple "if
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// statement", which has a very simple dominance structure. Basically, we
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// are trying to find the condition that is being branched on, which
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// subsequently causes this merge to happen. We really want control
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// dependence information for this check, but simplifycfg can't keep it up
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// to date, and this catches most of the cases we care about anyway.
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//
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BasicBlock *BB = PN->getParent();
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BasicBlock *IfTrue, *IfFalse;
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Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
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if (!IfCond) return false;
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DEBUG(std::cerr << "FOUND IF CONDITION! " << *IfCond << " T: "
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<< IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
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// Loop over the PHI's seeing if we can promote them all to select
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// instructions. While we are at it, keep track of the instructions
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// that need to be moved to the dominating block.
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std::set<Instruction*> AggressiveInsts;
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bool CanPromote = true;
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BasicBlock::iterator AfterPHIIt = BB->begin();
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while (isa<PHINode>(AfterPHIIt)) {
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PHINode *PN = cast<PHINode>(AfterPHIIt++);
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if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
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if (PN->getIncomingValue(0) != PN)
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PN->replaceAllUsesWith(PN->getIncomingValue(0));
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else
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PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
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} else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
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&AggressiveInsts) ||
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!DominatesMergePoint(PN->getIncomingValue(1), BB,
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&AggressiveInsts)) {
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CanPromote = false;
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}
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}
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// Did we eliminate all PHI's?
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if (!CanPromote && AfterPHIIt != BB->begin())
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return false;
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// If we all PHI nodes are promotable, check to make sure that all
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// instructions in the predecessor blocks can be promoted as well. If
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// not, we won't be able to get rid of the control flow, so it's not
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// worth promoting to select instructions.
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BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
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PN = cast<PHINode>(BB->begin());
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BasicBlock *Pred = PN->getIncomingBlock(0);
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if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
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IfBlock1 = Pred;
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DomBlock = *pred_begin(Pred);
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for (BasicBlock::iterator I = Pred->begin();
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!isa<TerminatorInst>(I); ++I)
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if (!AggressiveInsts.count(I)) {
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// This is not an aggressive instruction that we can promote.
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// Because of this, we won't be able to get rid of the control
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// flow, so the xform is not worth it.
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return false;
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}
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}
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Pred = PN->getIncomingBlock(1);
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if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
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IfBlock2 = Pred;
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DomBlock = *pred_begin(Pred);
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for (BasicBlock::iterator I = Pred->begin();
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!isa<TerminatorInst>(I); ++I)
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if (!AggressiveInsts.count(I)) {
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// This is not an aggressive instruction that we can promote.
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// Because of this, we won't be able to get rid of the control
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// flow, so the xform is not worth it.
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return false;
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}
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}
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// If we can still promote the PHI nodes after this gauntlet of tests,
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// do all of the PHI's now.
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// Move all 'aggressive' instructions, which are defined in the
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// conditional parts of the if's up to the dominating block.
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if (IfBlock1) {
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DomBlock->getInstList().splice(DomBlock->getTerminator(),
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IfBlock1->getInstList(),
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IfBlock1->begin(),
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IfBlock1->getTerminator());
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}
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if (IfBlock2) {
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DomBlock->getInstList().splice(DomBlock->getTerminator(),
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IfBlock2->getInstList(),
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IfBlock2->begin(),
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IfBlock2->getTerminator());
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}
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while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
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// Change the PHI node into a select instruction.
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Value *TrueVal =
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PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
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Value *FalseVal =
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PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
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std::string Name = PN->getName(); PN->setName("");
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PN->replaceAllUsesWith(new SelectInst(IfCond, TrueVal, FalseVal,
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Name, AfterPHIIt));
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BB->getInstList().erase(PN);
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}
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return true;
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}
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namespace {
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namespace {
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/// ConstantIntOrdering - This class implements a stable ordering of constant
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/// ConstantIntOrdering - This class implements a stable ordering of constant
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@ -1620,118 +1730,8 @@ bool llvm::SimplifyCFG(BasicBlock *BB) {
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// If there is a trivial two-entry PHI node in this basic block, and we can
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// If there is a trivial two-entry PHI node in this basic block, and we can
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// eliminate it, do so now.
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// eliminate it, do so now.
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if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
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if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
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if (PN->getNumIncomingValues() == 2) {
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if (PN->getNumIncomingValues() == 2)
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// Ok, this is a two entry PHI node. Check to see if this is a simple "if
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Changed |= FoldTwoEntryPHINode(PN);
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// statement", which has a very simple dominance structure. Basically, we
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// are trying to find the condition that is being branched on, which
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// subsequently causes this merge to happen. We really want control
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// dependence information for this check, but simplifycfg can't keep it up
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// to date, and this catches most of the cases we care about anyway.
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//
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BasicBlock *IfTrue, *IfFalse;
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if (Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse)) {
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DEBUG(std::cerr << "FOUND IF CONDITION! " << *IfCond << " T: "
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<< IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
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// Loop over the PHI's seeing if we can promote them all to select
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// instructions. While we are at it, keep track of the instructions
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// that need to be moved to the dominating block.
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std::set<Instruction*> AggressiveInsts;
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bool CanPromote = true;
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BasicBlock::iterator AfterPHIIt = BB->begin();
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while (isa<PHINode>(AfterPHIIt)) {
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PHINode *PN = cast<PHINode>(AfterPHIIt++);
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if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
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if (PN->getIncomingValue(0) != PN)
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PN->replaceAllUsesWith(PN->getIncomingValue(0));
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else
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PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
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} else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
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&AggressiveInsts) ||
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!DominatesMergePoint(PN->getIncomingValue(1), BB,
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&AggressiveInsts)) {
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CanPromote = false;
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break;
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}
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}
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// Did we eliminate all PHI's?
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CanPromote |= AfterPHIIt == BB->begin();
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// If we all PHI nodes are promotable, check to make sure that all
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// instructions in the predecessor blocks can be promoted as well. If
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// not, we won't be able to get rid of the control flow, so it's not
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// worth promoting to select instructions.
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BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
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if (CanPromote) {
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PN = cast<PHINode>(BB->begin());
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BasicBlock *Pred = PN->getIncomingBlock(0);
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if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
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IfBlock1 = Pred;
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DomBlock = *pred_begin(Pred);
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for (BasicBlock::iterator I = Pred->begin();
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!isa<TerminatorInst>(I); ++I)
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if (!AggressiveInsts.count(I)) {
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// This is not an aggressive instruction that we can promote.
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// Because of this, we won't be able to get rid of the control
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// flow, so the xform is not worth it.
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CanPromote = false;
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break;
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}
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}
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Pred = PN->getIncomingBlock(1);
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if (CanPromote &&
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cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
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IfBlock2 = Pred;
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DomBlock = *pred_begin(Pred);
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for (BasicBlock::iterator I = Pred->begin();
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!isa<TerminatorInst>(I); ++I)
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if (!AggressiveInsts.count(I)) {
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// This is not an aggressive instruction that we can promote.
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// Because of this, we won't be able to get rid of the control
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// flow, so the xform is not worth it.
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CanPromote = false;
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break;
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}
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}
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}
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// If we can still promote the PHI nodes after this gauntlet of tests,
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// do all of the PHI's now.
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if (CanPromote) {
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// Move all 'aggressive' instructions, which are defined in the
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// conditional parts of the if's up to the dominating block.
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if (IfBlock1) {
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DomBlock->getInstList().splice(DomBlock->getTerminator(),
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IfBlock1->getInstList(),
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IfBlock1->begin(),
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IfBlock1->getTerminator());
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}
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if (IfBlock2) {
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DomBlock->getInstList().splice(DomBlock->getTerminator(),
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IfBlock2->getInstList(),
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IfBlock2->begin(),
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IfBlock2->getTerminator());
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}
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while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
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// Change the PHI node into a select instruction.
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Value *TrueVal =
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PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
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Value *FalseVal =
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PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
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std::string Name = PN->getName(); PN->setName("");
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PN->replaceAllUsesWith(new SelectInst(IfCond, TrueVal, FalseVal,
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Name, AfterPHIIt));
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BB->getInstList().erase(PN);
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}
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Changed = true;
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}
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}
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}
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return Changed;
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return Changed;
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}
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}
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