Revert the main portion of r31856. It was causing BranchFolding

to break up CFG diamonds by banishing one of the blocks to the end of
the function, which is bad for code density and branch size.

This does pessimize MultiSource/Benchmarks/Ptrdist/yacr2, the
benchmark cited as the reason for the change, however I've examined
the code and it looks more like a case of gaming a particular
branch than of being generally applicable.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@84803 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 5 insertions, 5 deletions

diff --git a/lib/CodeGen/BranchFolding.cpp b/lib/CodeGen/BranchFolding.cpp
index f9abeacbdb..66c5aa5ff7 100644
--- a/lib/CodeGen/BranchFolding.cpp
+++ b/lib/CodeGen/BranchFolding.cpp
@@ -945,15 +945,15 @@ bool BranchFolder::OptimizeBlock(MachineBasicBlock *MBB) {
       }
     }
     
-    // If this block doesn't fall through (e.g. it ends with an uncond branch or
-    // has no successors) and if the pred falls through into this block, and if
-    // it would otherwise fall through into the block after this, move this
-    // block to the end of the function.
+    // If this block has no successors (e.g. it is a return block or ends with
+    // a call to a no-return function like abort or __cxa_throw) and if the pred
+    // falls through into this block, and if it would otherwise fall through
+    // into the block after this, move this block to the end of the function.
     //
     // We consider it more likely that execution will stay in the function (e.g.
     // due to loops) than it is to exit it.  This asserts in loops etc, moving
     // the assert condition out of the loop body.
-    if (!PriorCond.empty() && PriorFBB == 0 &&
+    if (MBB->succ_empty() && !PriorCond.empty() && PriorFBB == 0 &&
         MachineFunction::iterator(PriorTBB) == FallThrough &&
         !CanFallThrough(MBB)) {
       bool DoTransform = true;