Improve branch folding by recgonizing that explict successor relationships impact the value of fall-through choices.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@44785 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 5 insertions, 0 deletions

diff --git a/lib/CodeGen/BranchFolding.cpp b/lib/CodeGen/BranchFolding.cpp
index d4b1e90fd5..0f8c6629ba 100644
--- a/lib/CodeGen/BranchFolding.cpp
+++ b/lib/CodeGen/BranchFolding.cpp
@@ -775,6 +775,11 @@ static bool IsBetterFallthrough(MachineBasicBlock *MBB1,
   // optimize branches that branch to either a return block or an assert block
   // into a fallthrough to the return.
   if (MBB1->empty() || MBB2->empty()) return false;
+ 
+  // If there is a clear successor ordering we make sure that one block
+  // will fall through to the next
+  if (MBB1->isSuccessor(MBB2)) return true;
+  if (MBB2->isSuccessor(MBB1)) return false;
 
   MachineInstr *MBB1I = --MBB1->end();
   MachineInstr *MBB2I = --MBB2->end();