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Fix cast instructions that end up in bad places in GCC output
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@1117 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -354,6 +354,88 @@ bool CleanupGCCOutput::doOneCleanupPass(Method *M) {
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}
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// FixCastsAndPHIs - The LLVM GCC has a tendancy to intermix Cast instructions
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// in with the PHI nodes. These cast instructions are potentially there for two
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// different reasons:
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//
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// 1. The cast could be for an early PHI, and be accidentally inserted before
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// another PHI node. In this case, the PHI node should be moved to the end
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// of the PHI nodes in the basic block. We know that it is this case if
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// the source for the cast is a PHI node in this basic block.
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//
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// 2. If not #1, the cast must be a source argument for one of the PHI nodes
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// in the current basic block. If this is the case, the cast should be
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// lifted into the basic block for the appropriate predecessor.
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//
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static inline bool FixCastsAndPHIs(BasicBlock *BB) {
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bool Changed = false;
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BasicBlock::iterator InsertPos = BB->begin();
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// Find the end of the interesting instructions...
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while (isa<PHINode>(*InsertPos) || isa<CastInst>(*InsertPos)) ++InsertPos;
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// Back the InsertPos up to right after the last PHI node.
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while (InsertPos != BB->begin() && isa<CastInst>(*(InsertPos-1))) --InsertPos;
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// No PHI nodes, quick exit.
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if (InsertPos == BB->begin()) return false;
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// Loop over all casts trapped between the PHI's...
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BasicBlock::iterator I = BB->begin();
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while (I != InsertPos) {
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if (CastInst *CI = dyn_cast<CastInst>(*I)) { // Fix all cast instructions
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Value *Src = CI->getOperand(0);
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// Move the cast instruction to the current insert position...
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--InsertPos; // New position for cast to go...
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swap(*InsertPos, *I); // Cast goes down, PHI goes up
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if (isa<PHINode>(Src) && // Handle case #1
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cast<PHINode>(Src)->getParent() == BB) {
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// We're done for case #1
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} else { // Handle case #2
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// In case #2, we have to do a few things:
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// 1. Remove the cast from the current basic block.
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// 2. Identify the PHI node that the cast is for.
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// 3. Find out which predecessor the value is for.
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// 4. Move the cast to the end of the basic block that it SHOULD be
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//
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// Remove the cast instruction from the basic block. The remove only
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// invalidates iterators in the basic block that are AFTER the removed
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// element. Because we just moved the CastInst to the InsertPos, no
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// iterators get invalidated.
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//
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BB->getInstList().remove(InsertPos);
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// Find the PHI node. Since this cast was generated specifically for a
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// PHI node, there can only be a single PHI node using it.
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//
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assert(CI->use_size() == 1 && "Exactly one PHI node should use cast!");
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PHINode *PN = cast<PHINode>(*CI->use_begin());
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// Find out which operand of the PHI it is...
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unsigned i;
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for (i = 0; i < PN->getNumIncomingValues(); ++i)
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if (PN->getIncomingValue(i) == CI)
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break;
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assert(i != PN->getNumIncomingValues() && "PHI doesn't use cast!");
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// Get the predecessor the value is for...
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BasicBlock *Pred = PN->getIncomingBlock(i);
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// Reinsert the cast right before the terminator in Pred.
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Pred->getInstList().insert(Pred->end()-1, CI);
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}
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} else {
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++I;
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}
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}
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return Changed;
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}
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// RefactorPredecessor - When we find out that a basic block is a repeated
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// predecessor in a PHI node, we have to refactor the method until there is at
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@ -451,6 +533,8 @@ static bool fixLocalProblems(Method *M) {
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for (unsigned MI = 0; MI < M->size(); ++MI) {
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BasicBlock *BB = M->getBasicBlocks()[MI];
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Changed |= FixCastsAndPHIs(BB);
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if (isa<PHINode>(BB->front())) {
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const vector<BasicBlock*> Preds(BB->pred_begin(), BB->pred_end());
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