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());
   for (User *U : NarrowDef->users()) {
     Instruction *NarrowUser = cast<Instruction>(U);
 
Index: test/Transforms/IndVarSimplify/iv-zext.ll
===================================================================
--- test/Transforms/IndVarSimplify/iv-zext.ll
+++ test/Transforms/IndVarSimplify/iv-zext.ll
@@ -1,10 +1,11 @@
 ; RUN: opt < %s -indvars -S | FileCheck %s
-; CHECK-NOT: and
-; CHECK-NOT: zext
 
 target datalayout = "p:64:64:64-n32:64"
 
 define void @foo(double* %d, i64 %n) nounwind {
+; CHECK-LABEL: @foo(
+; CHECK-NOT: and
+; CHECK-NOT: zext
 entry:
 	br label %loop
 
@@ -31,3 +32,40 @@
 return:
 	ret void
 }
+
+; When widening IV, trunc and zext are not needed if the 
+; original 32-bit integer is known to be non-negative
+define void @foo1(i32* %A, i32* %B, i32* %C, i32 %N) {
+; CHECK-LABEL: @foo1(
+; CHECK-NOT: trunc
+; CHECK-NOT: zext
+entry:
+  br label %for.cond
+
+for.cond:                                      
+  %i.0 = phi i32 [ 0, %entry ], [ %inc, %for.inc ]
+  %cmp = icmp slt i32 %i.0, %N
+  br i1 %cmp, label %for.body, label %for.end
+
+for.body:                                    
+  %idxprom = sext i32 %i.0 to i64
+  %arrayidx = getelementptr inbounds i32, i32* %B, i64 %idxprom
+  %0 = load i32, i32* %arrayidx, align 4
+  %add = add nsw i32 %i.0, 1
+  %idxprom1 = zext i32 %add to i64
+  %arrayidx2 = getelementptr inbounds i32, i32* %C, i64 %idxprom1
+  %1 = load i32, i32* %arrayidx2, align 4
+  %add3 = add nsw i32 %0, %1
+  %idxprom4 = sext i32 %i.0 to i64
+  %arrayidx5 = getelementptr inbounds i32, i32* %A, i64 %idxprom4
+  store i32 %add3, i32* %arrayidx5, align 4
+  br label %for.inc
+
+for.inc:                                    
+  %inc = add nsw i32 %i.0, 1
+  br label %for.cond
+
+for.end:                    
+  ret void
+}
+