From 907dc2bc37f4b82c606cb62f52d0b2f0a9e7d557 Mon Sep 17 00:00:00 2001
From: Evan Cheng <evan.cheng@apple.com>
Date: Wed, 6 Aug 2008 18:04:43 +0000
Subject: [PATCH] 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
---
 .../Transforms/Scalar/LoopStrengthReduce.cpp  |  4 ++--
 .../2008-08-06-CmpStride.ll                   | 24 +++++++++++++++++++
 2 files changed, 26 insertions(+), 2 deletions(-)
 create mode 100644 llvm/test/Transforms/LoopStrengthReduce/2008-08-06-CmpStride.ll

diff --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 83bdb2cd176b..3d82fd279c54 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 000000000000..3700c69812dc
--- /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
+}