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Simplify this code. LoopDeletion doesn't need to explicit check that 

the loop exiting block dominates the latch block; if ScalarEvolution
can prove that the trip-count is finite, that's sufficient.

llvm-svn: 85165
This commit is contained in:
Dan Gohman 2009-10-26 22:18:58 +00:00
parent 672927f393
commit 34e38afa96
1 changed files with 2 additions and 24 deletions
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26
llvm/lib/Transforms/Scalar/LoopDeletion.cpp
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@ -33,8 +33,6 @@ namespace {
// Possibly eliminate loop L if it is dead.
bool runOnLoop(Loop* L, LPPassManager& LPM);
bool SingleDominatingExit(Loop* L,
SmallVector<BasicBlock*, 4>& exitingBlocks);
bool IsLoopDead(Loop* L, SmallVector<BasicBlock*, 4>& exitingBlocks,
SmallVector<BasicBlock*, 4>& exitBlocks,
bool &Changed, BasicBlock *Preheader);
@ -63,25 +61,6 @@ Pass* llvm::createLoopDeletionPass() {
return new LoopDeletion();
}
/// SingleDominatingExit - Checks that there is only a single blocks that
/// branches out of the loop, and that it also g the latch block. Loops
/// with multiple or non-latch-dominating exiting blocks could be dead, but we'd
/// have to do more extensive analysis to make sure, for instance, that the
/// control flow logic involved was or could be made loop-invariant.
bool LoopDeletion::SingleDominatingExit(Loop* L,
SmallVector<BasicBlock*, 4>& exitingBlocks) {
if (exitingBlocks.size() != 1)
return false;
BasicBlock* latch = L->getLoopLatch();
if (!latch)
return false;
DominatorTree& DT = getAnalysis<DominatorTree>();
return DT.dominates(exitingBlocks[0], latch);
}
/// IsLoopDead - Determined if a loop is dead. This assumes that we've already
/// checked for unique exit and exiting blocks, and that the code is in LCSSA
/// form.
@ -154,9 +133,8 @@ bool LoopDeletion::runOnLoop(Loop* L, LPPassManager& LPM) {
if (exitBlocks.size() != 1)
return false;
// Loops with multiple exits or exits that don't dominate the latch
// are too complicated to handle correctly.
if (!SingleDominatingExit(L, exitingBlocks))
// Loops with multiple exits are too complicated to handle correctly.
if (exitingBlocks.size() != 1)
return false;
// Finally, we have to check that the loop really is dead.