Insert IMPLICIT_DEFS for undef uses in tail merging

Tail merging can convert an undef use into a normal one when creating a
common tail. Doing so can make the register live out from a block which
previously contained the undef use. To keep the liveness up-to-date,
insert IMPLICIT_DEFs in such blocks when necessary.

To enable this patch the computeLiveIns() function which used to
compute live-ins for a block and set them immediately is split into new
functions:
- computeLiveIns() just computes the live-ins in a LivePhysRegs set.
- addLiveIns() applies the live-ins to a block live-in list.
- computeAndAddLiveIns() is a convenience function combining the other
  two functions and behaving like computeLiveIns() before this patch.

Based on a patch by Krzysztof Parzyszek <kparzysz@codeaurora.org>

Differential Revision: https://reviews.llvm.org/D37034

llvm-svn: 312668

1 files changed, 2 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/BranchRelaxation.cpp b/llvm/lib/CodeGen/BranchRelaxation.cpp
index 27ee12c4c5f..cbee43ecd20 100644
--- a/llvm/lib/CodeGen/BranchRelaxation.cpp
+++ b/llvm/lib/CodeGen/BranchRelaxation.cpp
@@ -259,7 +259,7 @@ MachineBasicBlock *BranchRelaxation::splitBlockBeforeInstr(MachineInstr &MI,
 
   // Need to fix live-in lists if we track liveness.
   if (TRI->trackLivenessAfterRegAlloc(*MF))
-    computeLiveIns(LiveRegs, MF->getRegInfo(), *NewBB);
+    computeAndAddLiveIns(LiveRegs, *NewBB);
 
   ++NumSplit;
 
@@ -348,7 +348,7 @@ bool BranchRelaxation::fixupConditionalBranch(MachineInstr &MI) {
 
     // Need to fix live-in lists if we track liveness.
     if (TRI->trackLivenessAfterRegAlloc(*MF))
-      computeLiveIns(LiveRegs, MF->getRegInfo(), NewBB);
+      computeAndAddLiveIns(LiveRegs, NewBB);
   }
 
   // We now have an appropriate fall-through block in place (either naturally or