[llvm] r271278 - Do not modify a std::vector while looping it.

[Yaron Keren via llvm-commits]

Author: yrnkrn
Date: Tue May 31 08:45:05 2016
New Revision: 271278

URL: http://llvm.org/viewvc/llvm-project?rev=271278&view=rev
Log:
Do not modify a std::vector while looping it. 

Introduced in r271244, this is probably undefined behaviour and asserts when
compiled with Visual C++ debug mode. 

On further note, the loop is quadratic with regard to the number of successors
since removeSuccessor is linear and could probably be modified to linear time.


Modified:
    llvm/trunk/lib/Target/X86/X86ISelLowering.cpp

Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=271278&r1=271277&r2=271278&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Tue May 31 08:45:05 2016
@@ -23841,8 +23841,12 @@ X86TargetLowering::EmitSjLjDispatchBlock
       Subtarget.getRegisterInfo()->getCalleeSavedRegs(MF);
   for (MachineBasicBlock *MBB : InvokeBBs) {
     // Remove the landing pad successor from the invoke block and replace it
-    // with the new dispatch block
-    for (auto MBBS : make_range(MBB->succ_rbegin(), MBB->succ_rend())) {
+    // with the new dispatch block.
+    // Keep a copy of Successors since it's modified inside the loop.
+    SmallVector<MachineBasicBlock *, 8> Successors(MBB->succ_rbegin(),
+                                                   MBB->succ_rend());
+    // FIXME: Avoid quadratic complexity.
+    for (auto MBBS : Successors) {
       if (MBBS->isEHPad()) {
         MBB->removeSuccessor(MBBS);
         MBBLPads.push_back(MBBS);