From: Petr Pavlu <petr.pavlu@arm.com>
Date: Mon, 16 Nov 2015 16:41:13 +0000 (+0000)
Subject: [ARM] Prevent use of a value pointed by end() iterator when placing a jump table
X-Git-Url: http://plrg.eecs.uci.edu/git/?p=oota-llvm.git;a=commitdiff_plain;h=1890cef0c5eea500cd3a54022d95f82fee313daf

[ARM] Prevent use of a value pointed by end() iterator when placing a jump table

Function ARMConstantIslands::doInitialJumpTablePlacement() iterates over all
basic blocks in a machine function. It calls `MI = MBB.getLastNonDebugInstr()`
to get the last instruction in each block and then uses MI->getOpcode() to
decide what to do. If getLastNonDebugInstr() returns MBB.end() (for example,
when the block does not contain any instructions) then calling getOpcode() on
this value is incorrect. Avoid this problem by checking the result of
getLastNonDebugInstr().

Differential Revision: http://reviews.llvm.org/D14694


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@253222 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Target/ARM/ARMConstantIslandPass.cpp b/lib/Target/ARM/ARMConstantIslandPass.cpp
index 416c5fd5cd7..0bf2d374df6 100644
--- a/lib/Target/ARM/ARMConstantIslandPass.cpp
+++ b/lib/Target/ARM/ARMConstantIslandPass.cpp
@@ -589,6 +589,8 @@ void ARMConstantIslands::doInitialJumpTablePlacement(
   MachineBasicBlock *LastCorrectlyNumberedBB = nullptr;
   for (MachineBasicBlock &MBB : *MF) {
     auto MI = MBB.getLastNonDebugInstr();
+    if (MI == MBB.end())
+      continue;
 
     unsigned JTOpcode;
     switch (MI->getOpcode()) {