Tail merging wasn't working for predecessors of landing pads. PR 1496.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@37427 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 22 insertions, 0 deletions

diff --git a/lib/CodeGen/BranchFolding.cpp b/lib/CodeGen/BranchFolding.cpp
index 2f25800cd0..ffde173e69 100644
--- a/lib/CodeGen/BranchFolding.cpp
+++ b/lib/CodeGen/BranchFolding.cpp
@@ -622,6 +622,28 @@ bool BranchFolder::TailMergeBlocks(MachineFunction &MF) {
             if (!FBB)
               FBB = next(MachineFunction::iterator(PBB));
           }
+          // Failing case:  the only way IBB can be reached from PBB is via
+          // exception handling.  Happens for landing pads.  Would be nice
+          // to have a bit in the edge so we didn't have to do all this.
+          if (IBB->isLandingPad()) {
+            MachineFunction::iterator IP = PBB;  IP++;
+            MachineBasicBlock* PredNextBB = NULL;
+            if (IP!=MF.end())
+              PredNextBB = IP;
+            if (TBB==NULL) {
+              if (IBB!=PredNextBB)      // fallthrough
+                continue;
+            } else if (FBB) {
+              if (TBB!=IBB && FBB!=IBB)   // cbr then ubr
+                continue;
+            } else if (Cond.size() == 0) {
+              if (TBB!=IBB)               // ubr
+                continue;
+            } else {
+              if (TBB!=IBB && IBB!=PredNextBB)  // cbr
+                continue;
+            }
+          }
           // Remove the unconditional branch at the end, if any.
           if (TBB && (Cond.size()==0 || FBB)) {
             TII->RemoveBranch(*PBB);