From 5614769d557600fda3cf73b481581fe32fbff258 Mon Sep 17 00:00:00 2001 From: Andrew Trick Date: Sat, 16 Jul 2011 01:18:53 +0000 Subject: [PATCH] indvars: fix a pass-sensitivity issue that would hit the SCEVExpander assertion I added in r135333. Check for the existence of a preheader before expanding a recurrence. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@135335 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/Scalar/IndVarSimplify.cpp | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp index 96a43cb6656..dee3d38d72a 100644 --- a/lib/Transforms/Scalar/IndVarSimplify.cpp +++ b/lib/Transforms/Scalar/IndVarSimplify.cpp @@ -140,7 +140,7 @@ namespace { void RewriteIVExpressions(Loop *L, SCEVExpander &Rewriter); - ICmpInst *LinearFunctionTestReplace(Loop *L, const SCEV *IVLimit, + ICmpInst *LinearFunctionTestReplace(Loop *L, const SCEV *BackedgeTakenCount, PHINode *IndVar, SCEVExpander &Rewriter); @@ -1823,7 +1823,18 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) { "canonical IV disrupted BackedgeTaken expansion"); assert(NeedCannIV && "LinearFunctionTestReplace requires a canonical induction variable"); - NewICmp = LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar, Rewriter); + // Check preconditions for proper SCEVExpander operation. SCEV does not + // express SCEVExpander's dependencies, such as LoopSimplify. Instead any + // pass that uses the SCEVExpander must do it. This does not work well for + // loop passes because SCEVExpander makes assumptions about all loops, while + // LoopPassManager only forces the current loop to be simplified. + // + // FIXME: SCEV expansion has no way to bail out, so the caller must + // explicitly check any assumptions made by SCEV. Brittle. + const SCEVAddRecExpr *AR = dyn_cast(BackedgeTakenCount); + if (!AR || AR->getLoop()->getLoopPreheader()) + NewICmp = + LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar, Rewriter); } // Rewrite IV-derived expressions. if (!DisableIVRewrite) -- 2.34.1