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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.

llvm-svn: 135335
This commit is contained in:
Andrew Trick 2011-07-16 01:18:53 +00:00
parent 9ea55dc2d6
commit c591f3afc3
1 changed files with 13 additions and 2 deletions
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15
llvm/lib/Transforms/Scalar/IndVarSimplify.cpp
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@ -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<SCEVAddRecExpr>(BackedgeTakenCount);
if (!AR || AR->getLoop()->getLoopPreheader())
NewICmp =
LinearFunctionTestReplace(L, BackedgeTakenCount, IndVar, Rewriter);
}
// Rewrite IV-derived expressions.
if (!DisableIVRewrite)