From c746503425fc04e25af680d244f9f351675210d5 Mon Sep 17 00:00:00 2001
From: Akira Hatanaka <ahatanaka@mips.com>
Date: Mon, 7 Oct 2013 19:13:53 +0000
Subject: [PATCH] [mips] Disable tail merging when long branch pass is enabled.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192124 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Target/Mips/MipsTargetMachine.cpp | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/lib/Target/Mips/MipsTargetMachine.cpp b/lib/Target/Mips/MipsTargetMachine.cpp
index 06f78e0ab36..5046c1b782f 100644
--- a/lib/Target/Mips/MipsTargetMachine.cpp
+++ b/lib/Target/Mips/MipsTargetMachine.cpp
@@ -135,7 +135,13 @@ namespace {
 class MipsPassConfig : public TargetPassConfig {
 public:
   MipsPassConfig(MipsTargetMachine *TM, PassManagerBase &PM)
-    : TargetPassConfig(TM, PM) {}
+    : TargetPassConfig(TM, PM) {
+    // The current implementation of long branch pass requires a scratch
+    // register ($at) to be available before branch instructions. Tail merging
+    // can break this requirement, so disable it when long branch pass is
+    // enabled.
+    EnableTailMerge = !getMipsSubtarget().enableLongBranchPass();
+  }
 
   MipsTargetMachine &getMipsTargetMachine() const {
     return getTM<MipsTargetMachine>();