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Split some code out of the main SimplifyCFG loop into its own function.
Fix said code to handle merging return instructions together correctly when handling multiple return values. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@50199 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
parent
3c02aca238
commit
c9e495c534
@ -1165,6 +1165,105 @@ static bool FoldTwoEntryPHINode(PHINode *PN) {
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return true;
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return true;
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}
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}
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/// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
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/// to two returning blocks, try to merge them together into one return,
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/// introducing a select if the return values disagree.
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static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
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assert(BI->isConditional() && "Must be a conditional branch");
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BasicBlock *TrueSucc = BI->getSuccessor(0);
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BasicBlock *FalseSucc = BI->getSuccessor(1);
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ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
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ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
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// Check to ensure both blocks are empty (just a return) or optionally empty
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// with PHI nodes. If there are other instructions, merging would cause extra
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// computation on one path or the other.
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BasicBlock::iterator BBI = TrueRet;
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if (BBI != TrueSucc->begin() && !isa<PHINode>(--BBI))
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return false; // Not empty with optional phi nodes.
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BBI = FalseRet;
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if (BBI != FalseSucc->begin() && !isa<PHINode>(--BBI))
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return false; // Not empty with optional phi nodes.
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// Okay, we found a branch that is going to two return nodes. If
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// there is no return value for this function, just change the
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// branch into a return.
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if (FalseRet->getNumOperands() == 0) {
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TrueSucc->removePredecessor(BI->getParent());
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FalseSucc->removePredecessor(BI->getParent());
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ReturnInst::Create(0, BI);
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BI->eraseFromParent();
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return true;
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}
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// Otherwise, build up the result values for the new return.
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SmallVector<Value*, 4> TrueResult;
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SmallVector<Value*, 4> FalseResult;
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for (unsigned i = 0, e = TrueRet->getNumOperands(); i != e; ++i) {
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// Otherwise, figure out what the true and false return values are
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// so we can insert a new select instruction.
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Value *TrueValue = TrueRet->getOperand(i);
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Value *FalseValue = FalseRet->getOperand(i);
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// Unwrap any PHI nodes in the return blocks.
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if (PHINode *TVPN = dyn_cast<PHINode>(TrueValue))
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if (TVPN->getParent() == TrueSucc)
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TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
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if (PHINode *FVPN = dyn_cast<PHINode>(FalseValue))
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if (FVPN->getParent() == FalseSucc)
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FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
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// In order for this transformation to be safe, we must be able to
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// unconditionally execute both operands to the return. This is
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// normally the case, but we could have a potentially-trapping
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// constant expression that prevents this transformation from being
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// safe.
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if (ConstantExpr *TCV = dyn_cast<ConstantExpr>(TrueValue))
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if (TCV->canTrap())
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return false;
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if (ConstantExpr *FCV = dyn_cast<ConstantExpr>(FalseValue))
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if (FCV->canTrap())
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return false;
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TrueResult.push_back(TrueValue);
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FalseResult.push_back(FalseValue);
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}
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// Okay, we collected all the mapped values and checked them for sanity, and
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// defined to really do this transformation. First, update the CFG.
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TrueSucc->removePredecessor(BI->getParent());
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FalseSucc->removePredecessor(BI->getParent());
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// Insert select instructions where needed.
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Value *BrCond = BI->getCondition();
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for (unsigned i = 0, e = TrueRet->getNumOperands(); i != e; ++i) {
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// Insert a select if the results differ.
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if (TrueResult[i] == FalseResult[i] || isa<UndefValue>(FalseResult[i]))
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continue;
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if (isa<UndefValue>(TrueResult[i])) {
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TrueResult[i] = FalseResult[i];
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continue;
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}
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TrueResult[i] = SelectInst::Create(BrCond, TrueResult[i],
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FalseResult[i], "retval", BI);
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}
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Value *RI = ReturnInst::Create(&TrueResult[0], TrueResult.size(), BI);
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DOUT << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
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<< "\n " << *BI << "NewRet = " << *RI
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<< "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc;
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BI->eraseFromParent();
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if (Instruction *BrCondI = dyn_cast<Instruction>(BrCond))
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ErasePossiblyDeadInstructionTree(BrCondI);
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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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/// integers that does not depend on their address. This is important for
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/// integers that does not depend on their address. This is important for
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@ -1292,73 +1391,12 @@ bool llvm::SimplifyCFG(BasicBlock *BB) {
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while (!CondBranchPreds.empty()) {
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while (!CondBranchPreds.empty()) {
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BranchInst *BI = CondBranchPreds.back();
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BranchInst *BI = CondBranchPreds.back();
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CondBranchPreds.pop_back();
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CondBranchPreds.pop_back();
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BasicBlock *TrueSucc = BI->getSuccessor(0);
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BasicBlock *FalseSucc = BI->getSuccessor(1);
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BasicBlock *OtherSucc = TrueSucc == BB ? FalseSucc : TrueSucc;
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// Check to see if the non-BB successor is also a return block.
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// Check to see if the non-BB successor is also a return block.
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if (isa<ReturnInst>(OtherSucc->getTerminator())) {
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if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
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// Check to see if there are only PHI instructions in this block.
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isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
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BasicBlock::iterator OSI = OtherSucc->getTerminator();
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SimplifyCondBranchToTwoReturns(BI))
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if (OSI == OtherSucc->begin() || isa<PHINode>(--OSI)) {
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return true;
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// Okay, we found a branch that is going to two return nodes. If
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// there is no return value for this function, just change the
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// branch into a return.
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if (RI->getNumOperands() == 0) {
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TrueSucc->removePredecessor(BI->getParent());
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FalseSucc->removePredecessor(BI->getParent());
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ReturnInst::Create(0, BI);
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BI->getParent()->getInstList().erase(BI);
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return true;
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}
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// Otherwise, figure out what the true and false return values are
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// so we can insert a new select instruction.
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Value *TrueValue = TrueSucc->getTerminator()->getOperand(0);
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Value *FalseValue = FalseSucc->getTerminator()->getOperand(0);
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// Unwrap any PHI nodes in the return blocks.
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if (PHINode *TVPN = dyn_cast<PHINode>(TrueValue))
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if (TVPN->getParent() == TrueSucc)
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TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
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if (PHINode *FVPN = dyn_cast<PHINode>(FalseValue))
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if (FVPN->getParent() == FalseSucc)
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FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
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// In order for this transformation to be safe, we must be able to
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// unconditionally execute both operands to the return. This is
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// normally the case, but we could have a potentially-trapping
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// constant expression that prevents this transformation from being
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// safe.
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if ((!isa<ConstantExpr>(TrueValue) ||
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!cast<ConstantExpr>(TrueValue)->canTrap()) &&
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(!isa<ConstantExpr>(TrueValue) ||
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!cast<ConstantExpr>(TrueValue)->canTrap())) {
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TrueSucc->removePredecessor(BI->getParent());
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FalseSucc->removePredecessor(BI->getParent());
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// Insert a new select instruction.
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Value *NewRetVal;
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Value *BrCond = BI->getCondition();
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if (TrueValue != FalseValue)
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NewRetVal = SelectInst::Create(BrCond, TrueValue,
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FalseValue, "retval", BI);
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else
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NewRetVal = TrueValue;
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DOUT << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
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<< "\n " << *BI << "Select = " << *NewRetVal
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<< "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc;
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ReturnInst::Create(NewRetVal, BI);
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BI->eraseFromParent();
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if (Instruction *BrCondI = dyn_cast<Instruction>(BrCond))
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if (isInstructionTriviallyDead(BrCondI))
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BrCondI->eraseFromParent();
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return true;
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}
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}
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}
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}
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}
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}
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}
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} else if (isa<UnwindInst>(BB->begin())) {
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} else if (isa<UnwindInst>(BB->begin())) {
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@ -0,0 +1,43 @@
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; RUN: llvm-as < %s | opt -simplifycfg -disable-output
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; rdar://5882392
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target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128"
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target triple = "x86_64-apple-darwin9"
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%struct.Py_complex = type { double, double }
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define %struct.Py_complex @_Py_c_pow(double %a.0, double %a.1, double %b.0, double %b.1) nounwind {
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entry:
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%tmp7 = fcmp une double %b.0, 0.000000e+00 ; <i1> [#uses=1]
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%tmp11 = fcmp une double %b.1, 0.000000e+00 ; <i1> [#uses=1]
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%bothcond = or i1 %tmp7, %tmp11 ; <i1> [#uses=1]
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br i1 %bothcond, label %bb15, label %bb53
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bb15: ; preds = %entry
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%tmp18 = fcmp une double %a.0, 0.000000e+00 ; <i1> [#uses=1]
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%tmp24 = fcmp une double %a.1, 0.000000e+00 ; <i1> [#uses=1]
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%bothcond1 = or i1 %tmp18, %tmp24 ; <i1> [#uses=1]
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br i1 %bothcond1, label %bb29, label %bb27
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bb27: ; preds = %bb15
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%tmp28 = call i32* @__error( ) nounwind ; <i32*> [#uses=1]
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store i32 33, i32* %tmp28, align 4
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ret double undef, double undef
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bb29: ; preds = %bb15
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%tmp36 = fcmp une double %b.1, 0.000000e+00 ; <i1> [#uses=1]
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br i1 %tmp36, label %bb39, label %bb47
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bb39: ; preds = %bb29
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br label %bb47
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bb47: ; preds = %bb39, %bb29
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ret double undef, double undef
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bb53: ; preds = %entry
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ret double undef, double undef
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}
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declare i32* @__error()
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declare double @pow(double, double) nounwind readonly
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declare double @cos(double) nounwind readonly
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