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Fix bug: test/Regression/Transforms/ADCE/2002-07-29-Segfault.ll

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llvm-svn: 3129
This commit is contained in:
Chris Lattner 2002-07-29 22:31:39 +00:00
parent 2f7ce877c5
commit 5aef91b716
1 changed files with 60 additions and 28 deletions
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88
lib/Transforms/Scalar/ADCE.cpp
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@ -8,6 +8,7 @@
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Type.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/iTerminators.h"
@ -209,41 +210,72 @@ bool ADCE::doADCE() {
BasicBlock *BB = I;
TerminatorInst *TI = BB->getTerminator();
// Loop over all of the successors, looking for ones that are not alive
for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
// Loop over all of the successors, looking for ones that are not alive.
// We cannot save the number of successors in the terminator instruction
// here because we may remove them if we don't have a postdominator...
//
for (unsigned i = 0; i != TI->getNumSuccessors(); ++i)
if (!AliveBlocks.count(TI->getSuccessor(i))) {
// Scan up the postdominator tree, looking for the first
// postdominator that is alive, and the last postdominator that is
// dead...
//
PostDominatorTree::Node *LastNode = DT[TI->getSuccessor(i)];
PostDominatorTree::Node *NextNode = LastNode->getIDom();
while (!AliveBlocks.count(NextNode->getNode())) {
LastNode = NextNode;
NextNode = NextNode->getIDom();
}
// Get the basic blocks that we need...
BasicBlock *LastDead = LastNode->getNode();
BasicBlock *NextAlive = NextNode->getNode();
// Make the conditional branch now go to the next alive block...
TI->getSuccessor(i)->removePredecessor(BB);
TI->setSuccessor(i, NextAlive);
// If there are PHI nodes in NextAlive, we need to add entries to
// the PHI nodes for the new incoming edge. The incoming values
// should be identical to the incoming values for LastDead.
// There is a special case here... if there IS no post-dominator for
// the block we have no owhere to point our branch to. Instead,
// convert it to a return. This can only happen if the code
// branched into an infinite loop. Note that this may not be
// desirable, because we _are_ altering the behavior of the code.
// This is a well known drawback of ADCE, so in the future if we
// choose to revisit the decision, this is where it should be.
//
for (BasicBlock::iterator II = NextAlive->begin();
PHINode *PN = dyn_cast<PHINode>(&*II); ++II) {
// Get the incoming value for LastDead...
int OldIdx = PN->getBasicBlockIndex(LastDead);
assert(OldIdx != -1 && "LastDead is not a pred of NextAlive!");
Value *InVal = PN->getIncomingValue(OldIdx);
// Add an incoming value for BB now...
PN->addIncoming(InVal, BB);
if (LastNode == 0) { // No postdominator!
// Call RemoveSuccessor to transmogrify the terminator instruction
// to not contain the outgoing branch, or to create a new
// terminator if the form fundementally changes (ie unconditional
// branch to return). Note that this will change a branch into an
// infinite loop into a return instruction!
//
RemoveSuccessor(TI, i);
// RemoveSuccessor may replace TI... make sure we have a fresh
// pointer... and e variable.
//
TI = BB->getTerminator();
// Rescan this successor...
--i;
} else {
PostDominatorTree::Node *NextNode = LastNode->getIDom();
while (!AliveBlocks.count(NextNode->getNode())) {
LastNode = NextNode;
NextNode = NextNode->getIDom();
}
// Get the basic blocks that we need...
BasicBlock *LastDead = LastNode->getNode();
BasicBlock *NextAlive = NextNode->getNode();
// Make the conditional branch now go to the next alive block...
TI->getSuccessor(i)->removePredecessor(BB);
TI->setSuccessor(i, NextAlive);
// If there are PHI nodes in NextAlive, we need to add entries to
// the PHI nodes for the new incoming edge. The incoming values
// should be identical to the incoming values for LastDead.
//
for (BasicBlock::iterator II = NextAlive->begin();
PHINode *PN = dyn_cast<PHINode>(&*II); ++II) {
// Get the incoming value for LastDead...
int OldIdx = PN->getBasicBlockIndex(LastDead);
assert(OldIdx != -1 && "LastDead is not a pred of NextAlive!");
Value *InVal = PN->getIncomingValue(OldIdx);
// Add an incoming value for BB now...
PN->addIncoming(InVal, BB);
}
}
}