Fix PR2355: bug in ChangeCompareStride. When the loop termination compare is the only use of its iv stride, the stride can be eliminated by moving it to another stride. If the scale is negative, swap the predicate instead of using a inverse predicate.

llvm-svn: 54415

2 files changed, 26 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 83bdb2cd176..3d82fd279c5 100644
--- a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -1624,10 +1624,10 @@ ICmpInst *LoopStrengthReduce::ChangeCompareStride(Loop *L, ICmpInst *Cond,
         continue;
       }
 
-      // If scale is negative, use inverse predicate unless it's testing
+      // If scale is negative, use swapped predicate unless it's testing
       // for equality.
       if (Scale < 0 && !Cond->isEquality())
-        Predicate = ICmpInst::getInversePredicate(Predicate);
+        Predicate = ICmpInst::getSwappedPredicate(Predicate);
 
       NewStride = &StrideOrder[i];
       break;
diff --git a/llvm/test/Transforms/LoopStrengthReduce/2008-08-06-CmpStride.ll b/llvm/test/Transforms/LoopStrengthReduce/2008-08-06-CmpStride.ll
new file mode 100644
index 00000000000..3700c69812d
--- /dev/null
+++ b/llvm/test/Transforms/LoopStrengthReduce/2008-08-06-CmpStride.ll
@@ -0,0 +1,24 @@
+; RUN: llvm-as < %s | opt -loop-reduce | llvm-dis | grep ugt
+; PR2355
+
+@.str = internal constant [4 x i8] c"%d\0A\00"
+
+declare i32 @printf(i8* noalias , ...) nounwind
+
+define i32 @main() nounwind {
+entry:
+        br label %forbody
+
+forbody:
+        %i.0 = phi i32 [ 0, %entry ], [ %inc, %forbody ]                ; <i32>[#uses=3]
+        %sub14 = sub i32 1027, %i.0             ; <i32> [#uses=1]
+        %mul15 = mul i32 %sub14, 10             ; <i32> [#uses=1]
+        %add166 = or i32 %mul15, 1              ; <i32> [#uses=1] *
+        call i32 (i8*, ...)* @printf( i8* noalias  getelementptr ([4 x i8]* @.str, i32 0, i32 0), i32 %add166 ) nounwind
+        %inc = add i32 %i.0, 1          ; <i32> [#uses=3]
+        %cmp = icmp ult i32 %inc, 1027          ; <i1> [#uses=1]
+        br i1 %cmp, label %forbody, label %afterfor
+
+afterfor:               ; preds = %forcond
+        ret i32 0
+}