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, 4 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/BranchFolding.h b/llvm/lib/CodeGen/BranchFolding.h
index 92681137e4c..f6efcb718c9 100644
--- a/llvm/lib/CodeGen/BranchFolding.h
+++ b/llvm/lib/CodeGen/BranchFolding.h
@@ -146,8 +146,8 @@ namespace llvm {
 
     /// Delete the instruction OldInst and everything after it, replacing it
     /// with an unconditional branch to NewDest.
-    void ReplaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
-                                 MachineBasicBlock *NewDest);
+    void replaceTailWithBranchTo(MachineBasicBlock::iterator OldInst,
+                                 MachineBasicBlock &NewDest);
 
     /// Given a machine basic block and an iterator into it, split the MBB so
     /// that the part before the iterator falls into the part starting at the
@@ -182,8 +182,8 @@ namespace llvm {
                                    unsigned &commonTailIndex);
 
     /// Create merged DebugLocs of identical instructions across SameTails and
-    /// assign it to the instruction in common tail.
-    void MergeCommonTailDebugLocs(unsigned commonTailIndex);
+    /// assign it to the instruction in common tail; merge MMOs and undef flags.
+    void mergeCommonTails(unsigned commonTailIndex);
 
     bool OptimizeBranches(MachineFunction &MF);