[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

1 files changed, 7 insertions, 1 deletions

diff --git a/lib/Target/Mips/MipsTargetMachine.cpp b/lib/Target/Mips/MipsTargetMachine.cpp
index 06f78e0..5046c1b 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>();