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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72496 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 834a95d731851df7186ce5a7723025b8a2147d7d..92270b5b64738b36b5afeac205c6e2a81719e112 100644 (file)
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/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;
     }

diff --git a/test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness-2.ll b/test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness-2.ll
index e3cb3a509535396bc836fe37995198b43724d4d2..f77aea393701d599bba27a510ffe477d53f49067 100644 (file)
--- a/test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness-2.ll
+++ b/test/Transforms/LoopStrengthReduce/change-compare-stride-trickiness-2.ll
@@ -31,3 +31,28 @@ if.end52:            ; preds = %for.cond.i.preheader
        %indvar.next689 = add i64 %indvar688, 1         ; <i64> [#uses=1]
        br i1 %phitmp654, label %for.cond.i.preheader, label %if.end
 }
+
+define void @promote(%struct.dumperinfo* %di) nounwind {
+entry:
+       br label %if.end
+
+if.end:                ; preds = %if.end52, %entry
+       br label %for.cond.i.preheader
+
+for.cond.i.preheader:          ; preds = %if.end52, %if.end
+       %indvar688 = phi i32 [ 0, %if.end ], [ %indvar.next689, %if.end52 ]             ; <i64> [#uses=3]
+       %tmp690 = shl i32 %indvar688, 12                ; <i64> [#uses=1]
+       %pa.0642 = add i32 %tmp690, 0           ; <i64> [#uses=1]
+       %tmp692693 = add i32 %indvar688, 1              ; <i32> [#uses=1]
+       %phitmp = sext i32 %tmp692693 to i64            ; <i64> [#uses=1]
+       br i1 false, label %if.end52, label %land.lhs.true.i
+
+land.lhs.true.i:               ; preds = %for.cond.i.preheader
+       %shr2.i = lshr i32 %pa.0642, 18         ; <i64> [#uses=0]
+       unreachable
+
+if.end52:              ; preds = %for.cond.i.preheader
+       %phitmp654 = icmp ult i64 %phitmp, 512          ; <i1> [#uses=1]
+       %indvar.next689 = add i32 %indvar688, 1         ; <i64> [#uses=1]
+       br i1 %phitmp654, label %for.cond.i.preheader, label %if.end
+}