From 546c4e6e848e7e05f9318a172838f7ad474f81e8 Mon Sep 17 00:00:00 2001
From: Rafael Auler <rafaelauler@fb.com>
Date: Wed, 21 Oct 2015 16:25:16 -0700
Subject: [PATCH] Fix bug in BinaryFunction::fixBranches() in llvm-flo

Summary:
When the ignore-nops patch landed, it exposed a bug in fixBranches()
where it ignored empty BBs. However, we cannot ignore empty BBs when it is
reordered and its fall-through changes. We must update it with a jump to the
original fall-through. This patch fixes this.

(cherry picked from FBD2568244)
---
 bolt/BinaryFunction.cpp | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/bolt/BinaryFunction.cpp b/bolt/BinaryFunction.cpp
index 9c7467b5cfd8..8eb462f1fa31 100644
--- a/bolt/BinaryFunction.cpp
+++ b/bolt/BinaryFunction.cpp
@@ -858,8 +858,6 @@ void BinaryFunction::fixBranches() {
 
   for (unsigned I = 0, E = BasicBlocksLayout.size(); I != E; ++I) {
     BinaryBasicBlock *BB = BasicBlocksLayout[I];
-    if (BB->begin() == BB->end())
-      continue;
 
     const MCSymbol *TBB = nullptr;
     const MCSymbol *FBB = nullptr;
@@ -884,7 +882,7 @@ void BinaryFunction::fixBranches() {
     if (CondBranch == nullptr && UncondBranch == nullptr) {
       // Case 1a: Last instruction is a return, so it does *not* fall through to
       // the next block.
-      if (MIA->isReturn(BB->back()))
+      if (!BB->empty() && MIA->isReturn(BB->back()))
         continue;
       // Case 1b: Layout has changed and the fallthrough is not the same. Need
       // to add a new unconditional branch to jump to the old fallthrough.