diff options
| -rw-r--r-- | lib/Transforms/Scalar/TailDuplication.cpp | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/lib/Transforms/Scalar/TailDuplication.cpp b/lib/Transforms/Scalar/TailDuplication.cpp index acf0db0ebe..43aaced378 100644 --- a/lib/Transforms/Scalar/TailDuplication.cpp +++ b/lib/Transforms/Scalar/TailDuplication.cpp @@ -127,6 +127,25 @@ bool TailDup::shouldEliminateUnconditionalBranch(TerminatorInst *TI) { for (; PI != PE; ++PI) if (TooMany-- == 0) return false; } + + // Finally, if this unconditional branch is a fall-through, be careful about + // tail duplicating it. In particular, we don't want to taildup it if the + // original block will still be there after taildup is completed: doing so + // would eliminate the fall-through, requiring unconditional branches. + Function::iterator DestI = Dest; + if (&*--DestI == BI->getParent()) { + // The uncond branch is a fall-through. Tail duplication of the block is + // will eliminate the fall-through-ness and end up cloning the terminator + // at the end of the Dest block. Since the original Dest block will + // continue to exist, this means that one or the other will not be able to + // fall through. One typical example that this helps with is code like: + // if (a) + // foo(); + // if (b) + // foo(); + // Cloning the 'if b' block into the end of the first foo block is messy. + return false; + } return true; } |