From a38cfb2fceb266bd78164021c08284dc59a1e8a3 Mon Sep 17 00:00:00 2001
From: Eli Friedman <eli.friedman@gmail.com>
Date: Wed, 6 Jul 2011 23:41:48 +0000
Subject: [PATCH] When tail-merging multiple blocks, make sure to correctly
 update the live-in list on the merged block to correctly account for the
 live-outs of all the predecessors.  They might not be the same in all cases
 (the testcase I have involves a PHI node where one of the operands is an
 IMPLICIT_DEF).

Unfortunately, the testcase I have is large and confidential, so I don't have a test to commit at the moment; I'll see if I can come up with something smaller where this issue reproduces.

<rdar://problem/9716278>



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134565 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/CodeGen/BranchFolding.cpp | 31 +++++++++++++++++++++----------
 lib/CodeGen/BranchFolding.h   |  2 ++
 2 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/lib/CodeGen/BranchFolding.cpp b/lib/CodeGen/BranchFolding.cpp
index 4df7b469294..99090a8269d 100644
--- a/lib/CodeGen/BranchFolding.cpp
+++ b/lib/CodeGen/BranchFolding.cpp
@@ -366,11 +366,31 @@ static unsigned ComputeCommonTailLength(MachineBasicBlock *MBB1,
   return TailLen;
 }
 
+void BranchFolder::MaintainLiveIns(MachineBasicBlock *CurMBB,
+                                   MachineBasicBlock *NewMBB) {
+  if (RS) {
+    RS->enterBasicBlock(CurMBB);
+    if (!CurMBB->empty())
+      RS->forward(prior(CurMBB->end()));
+    BitVector RegsLiveAtExit(TRI->getNumRegs());
+    RS->getRegsUsed(RegsLiveAtExit, false);
+    for (unsigned int i = 0, e = TRI->getNumRegs(); i != e; i++)
+      if (RegsLiveAtExit[i])
+        NewMBB->addLiveIn(i);
+  }
+}
+
 /// ReplaceTailWithBranchTo - Delete the instruction OldInst and everything
 /// after it, replacing it with an unconditional branch to NewDest.
 void BranchFolder::ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
                                            MachineBasicBlock *NewDest) {
+  MachineBasicBlock *CurMBB = OldInst->getParent();
+
   TII->ReplaceTailWithBranchTo(OldInst, NewDest);
+
+  // For targets that use the register scavenger, we must maintain LiveIns.
+  MaintainLiveIns(CurMBB, NewDest);
+
   ++NumTailMerge;
 }
 
@@ -399,16 +419,7 @@ MachineBasicBlock *BranchFolder::SplitMBBAt(MachineBasicBlock &CurMBB,
   NewMBB->splice(NewMBB->end(), &CurMBB, BBI1, CurMBB.end());
 
   // For targets that use the register scavenger, we must maintain LiveIns.
-  if (RS) {
-    RS->enterBasicBlock(&CurMBB);
-    if (!CurMBB.empty())
-      RS->forward(prior(CurMBB.end()));
-    BitVector RegsLiveAtExit(TRI->getNumRegs());
-    RS->getRegsUsed(RegsLiveAtExit, false);
-    for (unsigned int i = 0, e = TRI->getNumRegs(); i != e; i++)
-      if (RegsLiveAtExit[i])
-        NewMBB->addLiveIn(i);
-  }
+  MaintainLiveIns(&CurMBB, NewMBB);
 
   return NewMBB;
 }
diff --git a/lib/CodeGen/BranchFolding.h b/lib/CodeGen/BranchFolding.h
index 4ed42c03464..df795dfc248 100644
--- a/lib/CodeGen/BranchFolding.h
+++ b/lib/CodeGen/BranchFolding.h
@@ -95,6 +95,8 @@ namespace llvm {
     bool TailMergeBlocks(MachineFunction &MF);
     bool TryTailMergeBlocks(MachineBasicBlock* SuccBB,
                        MachineBasicBlock* PredBB);
+    void MaintainLiveIns(MachineBasicBlock *CurMBB,
+                         MachineBasicBlock *NewMBB);
     void ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
                                  MachineBasicBlock *NewDest);
     MachineBasicBlock *SplitMBBAt(MachineBasicBlock &CurMBB,
-- 
2.34.1