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Expose a smarter way to break critical edges.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@31256 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner
2006-10-28 06:44:56 +00:00
parent f6de8ad1a2
commit 27e1f90d85
2 changed files with 35 additions and 9 deletions
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lib/Transforms/Utils/BreakCriticalEdges.cpp
+24 -5
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@@ -100,10 +100,12 @@ bool llvm::isCriticalEdge(const TerminatorInst *TI, unsigned SuccNum) {
// SplitCriticalEdge - If this edge is a critical edge, insert a new node to
// split the critical edge. This will update DominatorSet, ImmediateDominator,
// DominatorTree, and DominatorFrontier information if it is available, thus
// calling this pass will not invalidate either of them. This returns true if
// the edge was split, false otherwise.
// calling this pass will not invalidate any of them. This returns true if
// the edge was split, false otherwise. This ensures that all edges to that
// dest go to one block instead of each going to a different block.
//
bool llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, Pass *P) {
bool llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, Pass *P,
bool MergeIdenticalEdges) {
if (!isCriticalEdge(TI, SuccNum)) return false;
BasicBlock *TIBB = TI->getParent();
BasicBlock *DestBB = TI->getSuccessor(SuccNum);
@@ -114,13 +116,13 @@ bool llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, Pass *P) {
// Create our unconditional branch...
new BranchInst(DestBB, NewBB);
// Branch to the new block, breaking the edge...
// Branch to the new block, breaking the edge.
TI->setSuccessor(SuccNum, NewBB);
// Insert the block into the function... right after the block TI lives in.
Function &F = *TIBB->getParent();
F.getBasicBlockList().insert(TIBB->getNext(), NewBB);
// If there are any PHI nodes in DestBB, we need to update them so that they
// merge incoming values from NewBB instead of from TIBB.
//
@@ -132,6 +134,23 @@ bool llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, Pass *P) {
int BBIdx = PN->getBasicBlockIndex(TIBB);
PN->setIncomingBlock(BBIdx, NewBB);
}
// If there are any other edges from TIBB to DestBB, update those to go
// through the split block, making those edges non-critical as well (and
// reducing the number of phi entries in the DestBB if relevant).
if (MergeIdenticalEdges) {
for (unsigned i = SuccNum+1, e = TI->getNumSuccessors(); i != e; ++i) {
if (TI->getSuccessor(i) != DestBB) continue;
// Remove an entry for TIBB from DestBB phi nodes.
DestBB->removePredecessor(TIBB);
// We found another edge to DestBB, go to NewBB instead.
TI->setSuccessor(i, NewBB);
}
}
// If we don't have a pass object, we can't update anything...
if (P == 0) return true;