From 0505181006f1088b2cb28a7240d5f27613783307 Mon Sep 17 00:00:00 2001
From: Scott Constable <scott.d.constable@intel.com>
Date: Fri, 10 Apr 2020 17:32:39 -0700
Subject: [PATCH] [X86] Fix to X86LoadValueInjectionRetHardeningPass for
 possible segfault

`MBB.back()` could segfault if `MBB.empty()`. Fixed by checking for `MBB.empty()` in the loop.

Differential Revision: https://reviews.llvm.org/D77584
---
 llvm/lib/Target/X86/X86LoadValueInjectionRetHardening.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/llvm/lib/Target/X86/X86LoadValueInjectionRetHardening.cpp b/llvm/lib/Target/X86/X86LoadValueInjectionRetHardening.cpp
index 9c36e86099f999..6e1134a259501a 100644
--- a/llvm/lib/Target/X86/X86LoadValueInjectionRetHardening.cpp
+++ b/llvm/lib/Target/X86/X86LoadValueInjectionRetHardening.cpp
@@ -99,6 +99,9 @@ bool X86LoadValueInjectionRetHardeningPass::runOnMachineFunction(
 
   bool Modified = false;
   for (auto &MBB : MF) {
+    if (MBB.empty())
+      continue;
+
     MachineInstr &MI = MBB.back();
     if (MI.getOpcode() != X86::RETQ)
       continue;