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Make loop-simplify produce better loops by turning PHI nodes like X = phi [X, Y]

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into just Y.  This often occurs when it seperates loops that have collapsed loop
headers.  This implements LoopSimplify/phi-node-simplify.ll


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@22746 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2005-08-10 02:07:32 +00:00
parent 8d56cdd0d1
commit 94f4032448
1 changed files with 16 additions and 1 deletions
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17
lib/Transforms/Utils/LoopSimplify.cpp
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@ -71,7 +71,7 @@ namespace {
AU.addPreserved<ImmediateDominators>(); AU.addPreserved<ImmediateDominators>();
AU.addPreserved<DominatorTree>(); AU.addPreserved<DominatorTree>();
AU.addPreserved<DominanceFrontier>(); AU.addPreserved<DominanceFrontier>();
AU.addPreservedID(BreakCriticalEdgesID); // No crit edges added.... AU.addPreservedID(BreakCriticalEdgesID); // No critical edges added.
} }
private: private:
bool ProcessLoop(Loop *L); bool ProcessLoop(Loop *L);
@ -190,8 +190,23 @@ bool LoopSimplify::ProcessLoop(Loop *L) {
Changed = true; Changed = true;
} }
// Scan over the PHI nodes in the loop header. Since they now have only two
// incoming values (the loop is canonicalized), we may have simplified the PHI
// down to 'X = phi [X, Y]', which should be replaced with 'Y'.
PHINode *PN;
DominatorSet &DS = getAnalysis<DominatorSet>();
for (BasicBlock::iterator I = L->getHeader()->begin();
(PN = dyn_cast<PHINode>(I++)); )
if (Value *V = PN->hasConstantValue(true))
if (!isa<Instruction>(V) ||
DS.dominates(cast<Instruction>(V)->getParent(), L->getHeader())) {
PN->replaceAllUsesWith(V);
PN->eraseFromParent();
}
for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
Changed |= ProcessLoop(*I); Changed |= ProcessLoop(*I);
return Changed; return Changed;
} }