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Implement testcase CFGSimplify/EqualPHIEdgeBlockMerge.ll 

llvm-svn: 5699
This commit is contained in:
Chris Lattner 2003-03-05 21:01:52 +00:00
parent 25743e9cda
commit 31116bafed
1 changed files with 24 additions and 10 deletions
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34
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
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@ -14,8 +14,9 @@
// PropagatePredecessors - This gets "Succ" ready to have the predecessors from
// "BB". This is a little tricky because "Succ" has PHI nodes, which need to
// have extra slots added to them to hold the merge edges from BB's
// predecessors. This function returns true (failure) if the Succ BB already
// has a predecessor that is a predecessor of BB.
// predecessors, and BB itself might have had PHI nodes in it. This function
// returns true (failure) if the Succ BB already has a predecessor that is a
// predecessor of BB and incoming PHI arguments would not be discernable.
//
// Assumption: Succ is the single successor for BB.
//
@ -31,12 +32,27 @@ static bool PropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
const std::vector<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB));
// Check to see if one of the predecessors of BB is already a predecessor of
// Succ. If so, we cannot do the transformation!
// Succ. If so, we cannot do the transformation if there are any PHI nodes
// with incompatible values coming in from the two edges!
//
for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
PI != PE; ++PI)
if (find(BBPreds.begin(), BBPreds.end(), *PI) != BBPreds.end())
return true;
for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ); PI != PE; ++PI)
if (find(BBPreds.begin(), BBPreds.end(), *PI) != BBPreds.end()) {
// Loop over all of the PHI nodes checking to see if there are
// incompatible values coming in.
BasicBlock::iterator BBI = Succ->begin();
while (PHINode *PN = dyn_cast<PHINode>(&*BBI++)) {
// Loop up the entries in the PHI node for BB and for *PI if the values
// coming in are non-equal, we cannot merge these two blocks (instead we
// should insert a conditional move or something, then merge the
// blocks).
int Idx1 = PN->getBasicBlockIndex(BB);
int Idx2 = PN->getBasicBlockIndex(*PI);
assert(Idx1 != -1 && Idx2 != -1 &&
"Didn't have entries for my predecessors??");
if (PN->getIncomingValue(Idx1) != PN->getIncomingValue(Idx2))
return true; // Values are not equal...
}
}
// Loop over all of the PHI nodes in the successor BB
for (BasicBlock::iterator I = Succ->begin();
@ -57,9 +73,7 @@ static bool PropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
// SimplifyCFG - This function is used to do simplification of a CFG. For
// example, it adjusts branches to branches to eliminate the extra hop, it
// eliminates unreachable basic blocks, and does other "peephole" optimization
// of the CFG. It returns true if a modification was made, and returns an
// iterator that designates the first element remaining after the block that
// was deleted.
// of the CFG. It returns true if a modification was made.
//
// WARNING: The entry node of a function may not be simplified.
//