From e60bb15982dc40517e078c3858fdc0716d43abb5 Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Thu, 8 Apr 2010 23:36:27 +0000
Subject: [PATCH] Avoid allocating a value of zero in a register if the initial
 formula inputs happen to negate each other.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@100828 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/LoopStrengthReduce.cpp | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index e50b13d63d5..4669b60e8d8 100644
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -262,11 +262,15 @@ void Formula::InitialMatch(const SCEV *S, Loop *L,
   SmallVector<const SCEV *, 4> Bad;
   DoInitialMatch(S, L, Good, Bad, SE, DT);
   if (!Good.empty()) {
-    BaseRegs.push_back(SE.getAddExpr(Good));
+    const SCEV *Sum = SE.getAddExpr(Good);
+    if (!Sum->isZero())
+      BaseRegs.push_back(Sum);
     AM.HasBaseReg = true;
   }
   if (!Bad.empty()) {
-    BaseRegs.push_back(SE.getAddExpr(Bad));
+    const SCEV *Sum = SE.getAddExpr(Bad);
+    if (!Sum->isZero())
+      BaseRegs.push_back(Sum);
     AM.HasBaseReg = true;
   }
 }
-- 
2.34.1