[PATCH] D18867: [IndVarSimplify] Eliminate zext of a signed IV when the IV is known to be non-negative

[Li Huang via llvm-commits]

lihuang created this revision.
lihuang added reviewers: sanjoy, reames, mbodart.
lihuang added a subscriber: llvm-commits.

[IndVarSimplify] Eliminate zext of a signed IV when widening if the IV is known to be non-negative.

This was part of a previous diff (D18777), now separated into a new diff. This change eliminates zexts of IV when IV is treated as unsigned and is known to be non-negative.

The change in D18777 will fail a front-end test (Frontend/optimization-remark-options.c) and this change should fix this test.

http://reviews.llvm.org/D18867

Files:
  lib/Transforms/Scalar/IndVarSimplify.cpp

Index: lib/Transforms/Scalar/IndVarSimplify.cpp
===================================================================
--- lib/Transforms/Scalar/IndVarSimplify.cpp
+++ lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -35,6 +35,7 @@
 #include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/CFG.h"
 #include "llvm/IR/Constants.h"
@@ -1304,7 +1305,8 @@
     }
   }
   // Our raison d'etre! Eliminate sign and zero extension.
-  if (IsSigned ? isa<SExtInst>(DU.NarrowUse) : isa<ZExtInst>(DU.NarrowUse)) {
+  if ((IsSigned ? isa<SExtInst>(DU.NarrowUse) : isa<ZExtInst>(DU.NarrowUse)) ||
+      (isa<ZExtInst>(DU.NarrowUse) && DU.NeverNegative)) {
     Value *NewDef = DU.WideDef;
     if (DU.NarrowUse->getType() != WideType) {
       unsigned CastWidth = SE->getTypeSizeInBits(DU.NarrowUse->getType());
@@ -1396,7 +1398,8 @@
   const SCEV *NarrowSCEV = SE->getSCEV(NarrowDef);
   bool NeverNegative =
       SE->isKnownPredicate(ICmpInst::ICMP_SGE, NarrowSCEV,
-                           SE->getConstant(NarrowSCEV->getType(), 0));
+                           SE->getConstant(NarrowSCEV->getType(), 0)) ||
+      isKnownNonNegative(NarrowDef, NarrowDef->getModule()->getDataLayout(), 0);
   for (User *U : NarrowDef->users()) {
     Instruction *NarrowUser = cast<Instruction>(U);
 


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