Two fixes. First, stop using the ugly shouldSubstituteIndVar method.
Second, disable substitution of quadratic addrec expressions to avoid putting
multiplies in loops!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@14358 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp
index 56f0213..5c4c63b 100644
--- a/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -602,7 +602,13 @@
if (PN->getType()->isInteger()) { // FIXME: when we have fast-math, enable!
SCEVHandle SCEV = SE->getSCEV(PN);
if (SCEV->hasComputableLoopEvolution(L))
- if (SE->shouldSubstituteIndVar(SCEV)) // HACK!
+ // FIXME: Without a strength reduction pass, it is an extremely bad idea
+ // to indvar substitute anything more complex than a linear induction
+ // variable. Doing so will put expensive multiply instructions inside
+ // of the loop. For now just disable indvar subst on anything more
+ // complex than a linear addrec.
+ if (!isa<SCEVAddRecExpr>(SCEV) ||
+ cast<SCEVAddRecExpr>(SCEV)->getNumOperands() < 3)
IndVars.push_back(std::make_pair(PN, SCEV));
}