Fix PR14361: wrong simplification of A+B==B+A. You may think that the old logic

replaced by this patch is equivalent to the new logic, but you'd be wrong, and
that's exactly where the bug was.  There's a similar bug in instsimplify which
manifests itself as instsimplify failing to simplify this, rather than doing it
wrong, see next commit.

llvm-svn: 168181

2 files changed, 32 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 8cb4a59cba9..e223a049f0b 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -2356,8 +2356,20 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
         // Try not to increase register pressure.
         BO0->hasOneUse() && BO1->hasOneUse()) {
       // Determine Y and Z in the form icmp (X+Y), (X+Z).
-      Value *Y = (A == C || A == D) ? B : A;
-      Value *Z = (C == A || C == B) ? D : C;
+      Value *Y, *Z;
+      if (A == C) {
+        Y = B;
+        Z = D;
+      } else if (A == D) {
+        Y = B;
+        Z = C;
+      } else if (B == C) {
+        Y = A;
+        Z = D;
+      } else if (B == D) {
+        Y = A;
+        Z = C;
+      }
       return new ICmpInst(Pred, Y, Z);
     }
 
diff --git a/llvm/test/Transforms/InstCombine/icmp.ll b/llvm/test/Transforms/InstCombine/icmp.ll
index eaff87d695e..8e064a4f2fc 100644
--- a/llvm/test/Transforms/InstCombine/icmp.ll
+++ b/llvm/test/Transforms/InstCombine/icmp.ll
@@ -659,3 +659,21 @@ define i1 @test64(i8 %a, i32 %b) nounwind {
 ; CHECK-NEXT: %c = icmp eq i8 %1, %a
 ; CHECK-NEXT: ret i1 %c
 }
+
+define i1 @test65(i64 %A, i64 %B) {
+  %s1 = add i64 %A, %B
+  %s2 = add i64 %A, %B
+  %cmp = icmp eq i64 %s1, %s2
+; CHECK: @test65
+; CHECK-NEXT: ret i1 true
+  ret i1 %cmp
+}
+
+define i1 @test66(i64 %A, i64 %B) {
+  %s1 = add i64 %A, %B
+  %s2 = add i64 %B, %A
+  %cmp = icmp eq i64 %s1, %s2
+; CHECK: @test66
+; CHECK-NEXT: ret i1 true
+  ret i1 %cmp
+}