From 12b5fa5f6e42eb8849d8b3bc7b1dbe676a6d8326 Mon Sep 17 00:00:00 2001
From: Jingyue Wu <jingyue@google.com>
Date: Wed, 13 May 2015 18:12:24 +0000
Subject: [PATCH] [NaryReassociate] avoid running forever

Avoid running forever by checking we are not reassociating an expression into
the same form.

Tested with @avoid_infinite_loops in nary-add.ll


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237269 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/NaryReassociate.cpp   | 12 ++++++++----
 test/Transforms/NaryReassociate/nary-add.ll | 11 +++++++++++
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/lib/Transforms/Scalar/NaryReassociate.cpp b/lib/Transforms/Scalar/NaryReassociate.cpp
index 7d3080dcd9b..af61068c97b 100644
--- a/lib/Transforms/Scalar/NaryReassociate.cpp
+++ b/lib/Transforms/Scalar/NaryReassociate.cpp
@@ -217,10 +217,14 @@ Instruction *NaryReassociate::tryReassociateAdd(Value *LHS, Value *RHS,
     //   = (A + RHS) + B or (B + RHS) + A
     const SCEV *AExpr = SE->getSCEV(A), *BExpr = SE->getSCEV(B);
     const SCEV *RHSExpr = SE->getSCEV(RHS);
-    if (auto *NewI = tryReassociatedAdd(SE->getAddExpr(AExpr, RHSExpr), B, I))
-      return NewI;
-    if (auto *NewI = tryReassociatedAdd(SE->getAddExpr(BExpr, RHSExpr), A, I))
-      return NewI;
+    if (BExpr != RHSExpr) {
+      if (auto *NewI = tryReassociatedAdd(SE->getAddExpr(AExpr, RHSExpr), B, I))
+        return NewI;
+    }
+    if (AExpr != RHSExpr) {
+      if (auto *NewI = tryReassociatedAdd(SE->getAddExpr(BExpr, RHSExpr), A, I))
+        return NewI;
+    }
   }
   return nullptr;
 }
diff --git a/test/Transforms/NaryReassociate/nary-add.ll b/test/Transforms/NaryReassociate/nary-add.ll
index 39d7c59ef9d..b3093ff6ecd 100644
--- a/test/Transforms/NaryReassociate/nary-add.ll
+++ b/test/Transforms/NaryReassociate/nary-add.ll
@@ -196,3 +196,14 @@ define void @iterative(i32 %a, i32 %b, i32 %c) {
 
   ret void
 }
+
+define void @avoid_infinite_loop(i32 %a, i32 %b) {
+; CHECK-LABEL: @avoid_infinite_loop
+  %ab = add i32 %a, %b
+; CHECK-NEXT: %ab
+  %ab2 = add i32 %ab, %b
+; CHECK-NEXT: %ab2
+  call void @foo(i32 %ab2)
+; CHECK-NEXT: @foo(i32 %ab2)
+  ret void
+}