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https://github.com/c64scene-ar/llvm-6502.git
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factor another large hunk of code out into its own function.
No functionality change. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@53530 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
parent
4f60e4de90
commit
867661ac8b
@ -1509,6 +1509,173 @@ static bool FoldBranchToCommonDest(BranchInst *BI) {
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return false;
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}
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/// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
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/// predecessor of another block, this function tries to simplify it. We know
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/// that PBI and BI are both conditional branches, and BI is in one of the
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/// successor blocks of PBI - PBI branches to BI.
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static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
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assert(PBI->isConditional() && BI->isConditional());
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BasicBlock *BB = BI->getParent();
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// If this block ends with a branch instruction, and if there is a
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// predecessor that ends on a branch of the same condition, make
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// this conditional branch redundant.
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if (PBI->getCondition() == BI->getCondition() &&
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PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
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// Okay, the outcome of this conditional branch is statically
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// knowable. If this block had a single pred, handle specially.
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if (BB->getSinglePredecessor()) {
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// Turn this into a branch on constant.
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bool CondIsTrue = PBI->getSuccessor(0) == BB;
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BI->setCondition(ConstantInt::get(Type::Int1Ty, CondIsTrue));
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return true; // Nuke the branch on constant.
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}
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// Otherwise, if there are multiple predecessors, insert a PHI that merges
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// in the constant and simplify the block result. Subsequent passes of
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// simplifycfg will thread the block.
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if (BlockIsSimpleEnoughToThreadThrough(BB)) {
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PHINode *NewPN = PHINode::Create(Type::Int1Ty,
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BI->getCondition()->getName() + ".pr",
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BB->begin());
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for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
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if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
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PBI != BI && PBI->isConditional() &&
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PBI->getCondition() == BI->getCondition() &&
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PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
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bool CondIsTrue = PBI->getSuccessor(0) == BB;
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NewPN->addIncoming(ConstantInt::get(Type::Int1Ty,
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CondIsTrue), *PI);
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} else {
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NewPN->addIncoming(BI->getCondition(), *PI);
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}
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BI->setCondition(NewPN);
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// This will thread the branch.
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return true;
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}
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}
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// If this is a conditional branch in an empty block, and if any
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// predecessors is a conditional branch to one of our destinations,
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// fold the conditions into logical ops and one cond br.
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if (&BB->front() == BI) {
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int PBIOp, BIOp;
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if (PBI->getSuccessor(0) == BI->getSuccessor(0)) {
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PBIOp = BIOp = 0;
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} else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) {
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PBIOp = 0; BIOp = 1;
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} else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) {
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PBIOp = 1; BIOp = 0;
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} else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) {
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PBIOp = BIOp = 1;
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} else {
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PBIOp = BIOp = -1;
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}
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// Check to make sure that the other destination of this branch
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// isn't BB itself. If so, this is an infinite loop that will
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// keep getting unwound.
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if (PBIOp != -1 && PBI->getSuccessor(PBIOp) == BB)
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PBIOp = BIOp = -1;
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// Do not perform this transformation if it would require
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// insertion of a large number of select instructions. For targets
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// without predication/cmovs, this is a big pessimization.
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if (PBIOp != -1) {
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BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
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unsigned NumPhis = 0;
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for (BasicBlock::iterator II = CommonDest->begin();
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isa<PHINode>(II); ++II, ++NumPhis) {
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if (NumPhis > 2) {
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// Disable this xform.
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PBIOp = -1;
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break;
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}
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}
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}
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// Finally, if everything is ok, fold the branches to logical ops.
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if (PBIOp != -1) {
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BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
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BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
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// If OtherDest *is* BB, then this is a basic block with just
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// a conditional branch in it, where one edge (OtherDesg) goes
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// back to the block. We know that the program doesn't get
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// stuck in the infinite loop, so the condition must be such
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// that OtherDest isn't branched through. Forward to CommonDest,
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// and avoid an infinite loop at optimizer time.
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if (OtherDest == BB)
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OtherDest = CommonDest;
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DOUT << "FOLDING BRs:" << *PBI->getParent()
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<< "AND: " << *BI->getParent();
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DOUT << *PBI->getParent()->getParent();
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// BI may have other predecessors. Because of this, we leave
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// it alone, but modify PBI.
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// Make sure we get to CommonDest on True&True directions.
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Value *PBICond = PBI->getCondition();
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if (PBIOp)
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PBICond = BinaryOperator::CreateNot(PBICond,
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PBICond->getName()+".not",
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PBI);
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Value *BICond = BI->getCondition();
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if (BIOp)
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BICond = BinaryOperator::CreateNot(BICond,
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BICond->getName()+".not",
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PBI);
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// Merge the conditions.
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Value *Cond =
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BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
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// Modify PBI to branch on the new condition to the new dests.
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PBI->setCondition(Cond);
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PBI->setSuccessor(0, CommonDest);
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PBI->setSuccessor(1, OtherDest);
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// OtherDest may have phi nodes. If so, add an entry from PBI's
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// block that are identical to the entries for BI's block.
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PHINode *PN;
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for (BasicBlock::iterator II = OtherDest->begin();
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(PN = dyn_cast<PHINode>(II)); ++II) {
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Value *V = PN->getIncomingValueForBlock(BB);
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PN->addIncoming(V, PBI->getParent());
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}
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// We know that the CommonDest already had an edge from PBI to
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// it. If it has PHIs though, the PHIs may have different
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// entries for BB and PBI's BB. If so, insert a select to make
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// them agree.
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for (BasicBlock::iterator II = CommonDest->begin();
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(PN = dyn_cast<PHINode>(II)); ++II) {
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Value * BIV = PN->getIncomingValueForBlock(BB);
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unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
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Value *PBIV = PN->getIncomingValue(PBBIdx);
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if (BIV != PBIV) {
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// Insert a select in PBI to pick the right value.
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Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
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PBIV->getName()+".mux", PBI);
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PN->setIncomingValue(PBBIdx, NV);
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}
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}
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DOUT << "INTO: " << *PBI->getParent();
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DOUT << *PBI->getParent()->getParent();
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// This basic block is probably dead. We know it has at least
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// one fewer predecessor.
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return true;
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}
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}
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return false;
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}
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namespace {
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/// ConstantIntOrdering - This class implements a stable ordering of constant
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@ -1745,163 +1912,13 @@ bool llvm::SimplifyCFG(BasicBlock *BB) {
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if (FoldBranchToCommonDest(BI))
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return SimplifyCFG(BB) | 1;
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// Scan predessor blocks for conditional branches.
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// Scan predecessor blocks for conditional branches.
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for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
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if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
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if (PBI != BI && PBI->isConditional()) {
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// If this block ends with a branch instruction, and if there is a
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// predecessor that ends on a branch of the same condition, make
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// this conditional branch redundant.
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if (PBI->getCondition() == BI->getCondition() &&
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PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
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// Okay, the outcome of this conditional branch is statically
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// knowable. If this block had a single pred, handle specially.
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if (BB->getSinglePredecessor()) {
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// Turn this into a branch on constant.
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bool CondIsTrue = PBI->getSuccessor(0) == BB;
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BI->setCondition(ConstantInt::get(Type::Int1Ty, CondIsTrue));
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return SimplifyCFG(BB); // Nuke the branch on constant.
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}
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// Otherwise, if there are multiple predecessors, insert a PHI
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// that merges in the constant and simplify the block result.
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if (BlockIsSimpleEnoughToThreadThrough(BB)) {
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PHINode *NewPN = PHINode::Create(Type::Int1Ty,
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BI->getCondition()->getName()
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+ ".pr", BB->begin());
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for (PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
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if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
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PBI != BI && PBI->isConditional() &&
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PBI->getCondition() == BI->getCondition() &&
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PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
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bool CondIsTrue = PBI->getSuccessor(0) == BB;
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NewPN->addIncoming(ConstantInt::get(Type::Int1Ty,
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CondIsTrue), *PI);
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} else {
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NewPN->addIncoming(BI->getCondition(), *PI);
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}
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BI->setCondition(NewPN);
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// This will thread the branch.
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return SimplifyCFG(BB) | true;
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}
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}
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// If this is a conditional branch in an empty block, and if any
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// predecessors is a conditional branch to one of our destinations,
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// fold the conditions into logical ops and one cond br.
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if (&BB->front() == BI) {
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int PBIOp, BIOp;
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if (PBI->getSuccessor(0) == BI->getSuccessor(0)) {
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PBIOp = BIOp = 0;
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} else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) {
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PBIOp = 0; BIOp = 1;
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} else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) {
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PBIOp = 1; BIOp = 0;
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} else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) {
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PBIOp = BIOp = 1;
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} else {
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PBIOp = BIOp = -1;
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}
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// Check to make sure that the other destination of this branch
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// isn't BB itself. If so, this is an infinite loop that will
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// keep getting unwound.
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if (PBIOp != -1 && PBI->getSuccessor(PBIOp) == BB)
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PBIOp = BIOp = -1;
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// Do not perform this transformation if it would require
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// insertion of a large number of select instructions. For targets
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// without predication/cmovs, this is a big pessimization.
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if (PBIOp != -1) {
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BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
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unsigned NumPhis = 0;
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for (BasicBlock::iterator II = CommonDest->begin();
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isa<PHINode>(II); ++II, ++NumPhis) {
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if (NumPhis > 2) {
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// Disable this xform.
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PBIOp = -1;
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break;
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}
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}
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}
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// Finally, if everything is ok, fold the branches to logical ops.
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if (PBIOp != -1) {
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BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
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BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
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// If OtherDest *is* BB, then this is a basic block with just
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// a conditional branch in it, where one edge (OtherDesg) goes
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// back to the block. We know that the program doesn't get
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// stuck in the infinite loop, so the condition must be such
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// that OtherDest isn't branched through. Forward to CommonDest,
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// and avoid an infinite loop at optimizer time.
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if (OtherDest == BB)
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OtherDest = CommonDest;
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DOUT << "FOLDING BRs:" << *PBI->getParent()
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<< "AND: " << *BI->getParent();
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// BI may have other predecessors. Because of this, we leave
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// it alone, but modify PBI.
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// Make sure we get to CommonDest on True&True directions.
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Value *PBICond = PBI->getCondition();
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if (PBIOp)
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PBICond = BinaryOperator::CreateNot(PBICond,
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PBICond->getName()+".not",
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PBI);
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Value *BICond = BI->getCondition();
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if (BIOp)
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BICond = BinaryOperator::CreateNot(BICond,
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BICond->getName()+".not",
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PBI);
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// Merge the conditions.
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Value *Cond =
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BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
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// Modify PBI to branch on the new condition to the new dests.
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PBI->setCondition(Cond);
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PBI->setSuccessor(0, CommonDest);
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PBI->setSuccessor(1, OtherDest);
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// OtherDest may have phi nodes. If so, add an entry from PBI's
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// block that are identical to the entries for BI's block.
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PHINode *PN;
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for (BasicBlock::iterator II = OtherDest->begin();
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(PN = dyn_cast<PHINode>(II)); ++II) {
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Value *V = PN->getIncomingValueForBlock(BB);
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PN->addIncoming(V, PBI->getParent());
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}
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// We know that the CommonDest already had an edge from PBI to
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// it. If it has PHIs though, the PHIs may have different
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// entries for BB and PBI's BB. If so, insert a select to make
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// them agree.
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for (BasicBlock::iterator II = CommonDest->begin();
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(PN = dyn_cast<PHINode>(II)); ++II) {
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Value * BIV = PN->getIncomingValueForBlock(BB);
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unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
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Value *PBIV = PN->getIncomingValue(PBBIdx);
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if (BIV != PBIV) {
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// Insert a select in PBI to pick the right value.
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Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
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PBIV->getName()+".mux", PBI);
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PN->setIncomingValue(PBBIdx, NV);
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}
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}
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DOUT << "INTO: " << *PBI->getParent();
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// This basic block is probably dead. We know it has at least
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// one fewer predecessor.
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return SimplifyCFG(BB) | true;
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}
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}
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}
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if (PBI != BI && PBI->isConditional())
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if (SimplifyCondBranchToCondBranch(PBI, BI))
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return SimplifyCFG(BB) | true;
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}
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} else if (isa<UnreachableInst>(BB->getTerminator())) {
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// If there are any instructions immediately before the unreachable that can
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