1 files changed, 14 insertions, 6 deletions

diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp
index d51e034..235aaaa 100644
--- a/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -532,7 +532,8 @@ void IndVarSimplify::RewriteLoopExitValues(Loop *L, SCEVExpander &Rewriter) {
         // and varies predictably *inside* the loop.  Evaluate the value it
         // contains when the loop exits, if possible.
         const SCEV *ExitValue = SE->getSCEVAtScope(Inst, L->getParentLoop());
-        if (!SE->isLoopInvariant(ExitValue, L) || !isSafeToExpand(ExitValue))
+        if (!SE->isLoopInvariant(ExitValue, L) ||
+            !isSafeToExpand(ExitValue, *SE))
           continue;
 
         // Computing the value outside of the loop brings no benefit if :
@@ -1479,8 +1480,14 @@ static Value *genLoopLimit(PHINode *IndVar, const SCEV *IVCount, Loop *L,
   if (IndVar->getType()->isPointerTy()
       && !IVCount->getType()->isPointerTy()) {
 
+    // IVOffset will be the new GEP offset that is interpreted by GEP as a
+    // signed value. IVCount on the other hand represents the loop trip count,
+    // which is an unsigned value. FindLoopCounter only allows induction
+    // variables that have a positive unit stride of one. This means we don't
+    // have to handle the case of negative offsets (yet) and just need to zero
+    // extend IVCount.
     Type *OfsTy = SE->getEffectiveSCEVType(IVInit->getType());
-    const SCEV *IVOffset = SE->getTruncateOrSignExtend(IVCount, OfsTy);
+    const SCEV *IVOffset = SE->getTruncateOrZeroExtend(IVCount, OfsTy);
 
     // Expand the code for the iteration count.
     assert(SE->isLoopInvariant(IVOffset, L) &&
@@ -1492,7 +1499,7 @@ static Value *genLoopLimit(PHINode *IndVar, const SCEV *IVCount, Loop *L,
     assert(AR->getStart() == SE->getSCEV(GEPBase) && "bad loop counter");
     // We could handle pointer IVs other than i8*, but we need to compensate for
     // gep index scaling. See canExpandBackedgeTakenCount comments.
-    assert(SE->getSizeOfExpr(
+    assert(SE->getSizeOfExpr(IntegerType::getInt64Ty(IndVar->getContext()),
              cast<PointerType>(GEPBase->getType())->getElementType())->isOne()
            && "unit stride pointer IV must be i8*");
 
@@ -1506,9 +1513,10 @@ static Value *genLoopLimit(PHINode *IndVar, const SCEV *IVCount, Loop *L,
     // BECount = (IVEnd - IVInit - 1) => IVLimit = IVInit (postinc).
     //
     // Valid Cases: (1) both integers is most common; (2) both may be pointers
-    // for simple memset-style loops; (3) IVInit is an integer and IVCount is a
-    // pointer may occur when enable-iv-rewrite generates a canonical IV on top
-    // of case #2.
+    // for simple memset-style loops.
+    //
+    // IVInit integer and IVCount pointer would only occur if a canonical IV
+    // were generated on top of case #2, which is not expected.
 
     const SCEV *IVLimit = 0;
     // For unit stride, IVCount = Start + BECount with 2's complement overflow.