[SCEV] Disable canonical expansion for non-affine addrecs.

Reviewed By: apilipenko

Differential Revision: https://reviews.llvm.org/D65276

Patch by Evgeniy Brevnov (ybrevnov@azul.com)

llvm-svn: 372789

1 files changed, 12 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolutionExpander.cpp b/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
index e8a95d35482..251717f64e0 100644
--- a/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
@@ -1486,7 +1486,18 @@ Value *SCEVExpander::expandAddRecExprLiterally(const SCEVAddRecExpr *S) {
 }
 
 Value *SCEVExpander::visitAddRecExpr(const SCEVAddRecExpr *S) {
-  if (!CanonicalMode) return expandAddRecExprLiterally(S);
+  // In canonical mode we compute the addrec as an expression of a canonical IV
+  // using evaluateAtIteration and expand the resulting SCEV expression. This
+  // way we avoid introducing new IVs to carry on the comutation of the addrec
+  // throughout the loop.
+  //
+  // For nested addrecs evaluateAtIteration might need a canonical IV of a
+  // type wider than the addrec itself. Emitting a canonical IV of the
+  // proper type might produce non-legal types, for example expanding an i64
+  // {0,+,2,+,1} addrec would need an i65 canonical IV. To avoid this just fall
+  // back to non-canonical mode for nested addrecs.
+  if (!CanonicalMode || (S->getNumOperands() > 2))
+    return expandAddRecExprLiterally(S);
 
   Type *Ty = SE.getEffectiveSCEVType(S->getType());
   const Loop *L = S->getLoop();