Revert 72493 and replace it with a more conservative fix, for now: don't

rewrite the comparison if there is any implicit extension or truncation
on the induction variable. I'm planning for IVUsers to eventually take
over some of the work of this code, and for it to be generalized.

llvm-svn: 72496

1 files changed, 8 insertions, 7 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 834a95d7318..92270b5b647 100644
--- a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -1993,6 +1993,12 @@ ICmpInst *LoopStrengthReduce::ChangeCompareStride(Loop *L, ICmpInst *Cond,
           ValidScale(!CommonExprs->isZero(), Scale, UsersToProcess))
         continue;
 
+      // Avoid rewriting the compare instruction with an iv which has
+      // implicit extension or truncation built into it.
+      // TODO: This is over-conservative.
+      if (SE->getTypeSizeInBits(CondUse->getOffset()->getType()) != TyBits)
+        continue;
+
       // If scale is negative, use swapped predicate unless it's testing
       // for equality.
       if (Scale < 0 && !Cond->isEquality())
@@ -2005,16 +2011,11 @@ ICmpInst *LoopStrengthReduce::ChangeCompareStride(Loop *L, ICmpInst *Cond,
         ConstantInt *CI = ConstantInt::get(NewCmpIntTy, NewCmpVal);
         NewCmpRHS = ConstantExpr::getIntToPtr(CI, NewCmpTy);
       }
-      NewOffset = CondUse->getOffset();
-      if (CondUse->isSigned())
-        NewOffset = SE->getNoopOrSignExtend(CondUse->getOffset(), NewCmpTy);
-      else
-        NewOffset = SE->getNoopOrZeroExtend(CondUse->getOffset(), NewCmpTy);
       NewOffset = TyBits == NewTyBits
-        ? SE->getMulExpr(NewOffset,
+        ? SE->getMulExpr(CondUse->getOffset(),
                          SE->getConstant(ConstantInt::get(CmpTy, Scale)))
         : SE->getConstant(ConstantInt::get(NewCmpIntTy,
-          cast<SCEVConstant>(NewOffset)->getValue()
+          cast<SCEVConstant>(CondUse->getOffset())->getValue()
             ->getSExtValue()*Scale));
       break;
     }