Re-apply r101000, with a fix: Don't eliminate an icmp which is part of
the loop exit test. This usually doesn't come up for a variety of
reasons, but it isn't impossible, so make IndVarSimplify handle it
conservatively.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@101008 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp
index f87d693..5dbde99 100644
--- a/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -97,6 +97,7 @@
private:
+ void EliminateIVComparisons();
void RewriteNonIntegerIVs(Loop *L);
ICmpInst *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount,
@@ -336,6 +337,40 @@
SE->forgetLoop(L);
}
+void IndVarSimplify::EliminateIVComparisons() {
+ // Look for ICmp users.
+ for (IVUsers::iterator I = IU->begin(), E = IU->end(); I != E;) {
+ IVStrideUse &UI = *I++;
+ ICmpInst *ICmp = dyn_cast<ICmpInst>(UI.getUser());
+ if (!ICmp) continue;
+
+ bool Swapped = UI.getOperandValToReplace() == ICmp->getOperand(1);
+ ICmpInst::Predicate Pred = ICmp->getPredicate();
+ if (Swapped) Pred = ICmpInst::getSwappedPredicate(Pred);
+
+ // Get the SCEVs for the ICmp operands.
+ const SCEV *S = IU->getReplacementExpr(UI);
+ const SCEV *X = SE->getSCEV(ICmp->getOperand(!Swapped));
+
+ // Simplify unnecessary loops away.
+ const Loop *ICmpLoop = LI->getLoopFor(ICmp->getParent());
+ S = SE->getSCEVAtScope(S, ICmpLoop);
+ X = SE->getSCEVAtScope(X, ICmpLoop);
+
+ // If the condition is always true or always false, replace it with
+ // a constant value.
+ if (SE->isKnownPredicate(Pred, S, X))
+ ICmp->replaceAllUsesWith(ConstantInt::getTrue(ICmp->getContext()));
+ else if (SE->isKnownPredicate(ICmpInst::getInversePredicate(Pred), S, X))
+ ICmp->replaceAllUsesWith(ConstantInt::getFalse(ICmp->getContext()));
+ else
+ continue;
+
+ DEBUG(dbgs() << "INDVARS: Eliminated comparison: " << *ICmp << '\n');
+ ICmp->eraseFromParent();
+ }
+}
+
bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
IU = &getAnalysis<IVUsers>();
LI = &getAnalysis<LoopInfo>();
@@ -427,10 +462,19 @@
ExitingBlock) {
assert(NeedCannIV &&
"LinearFunctionTestReplace requires a canonical induction variable");
+
// Can't rewrite non-branch yet.
- if (BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator()))
+ if (BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator())) {
+ // Eliminate comparisons which are always true or always false, due to
+ // the known backedge-taken count. This may include comparisons which
+ // are currently controlling (part of) the loop exit, so we can only do
+ // it when we know we're going to insert our own loop exit code.
+ EliminateIVComparisons();
+
+ // Insert new loop exit code.
NewICmp = LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar,
ExitingBlock, BI, Rewriter);
+ }
}
// Rewrite IV-derived expressions. Clears the rewriter cache.