[llvm] r254794 - CodeGen: Move the SlotIndexes BumpPtrAllocator before the list it allocates

[Justin Bogner via llvm-commits]

Author: bogner
Date: Fri Dec  4 17:00:54 2015
New Revision: 254794

URL: http://llvm.org/viewvc/llvm-project?rev=254794&view=rev
Log:
CodeGen: Move the SlotIndexes BumpPtrAllocator before the list it allocates

When a `SlotIndexes` is destroyed, `ileAllocator` will currently be
destructed before `IndexList`, but all of `IndexList`'s storage has
been allocated by `ileAllocator`. This means we'll call destructors on
garbage data, which is very bad. This can be avoided by putting the
BumpPtrAllocator earlier in the class than anything it allocates.

Unfortunately, I don't know how to test this. It depends very much on
memory layout, and the only evidence I have that this is actually
happening in practice are backtraces that might be explained by this.
By inspection though, the code is obviously dangerous/wrong, and this
is the right thing to do.

I'll follow up later with a patch that calls clearAndLeakNodesUnsafely
on the list, since there isn't much point in destructing them when
they're allocated in a BPA anyway, but I figured it makes sense to
commit the correctness fix separately from that optimization.

Modified:
    llvm/trunk/include/llvm/CodeGen/SlotIndexes.h

Modified: llvm/trunk/include/llvm/CodeGen/SlotIndexes.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/CodeGen/SlotIndexes.h?rev=254794&r1=254793&r2=254794&view=diff
==============================================================================
--- llvm/trunk/include/llvm/CodeGen/SlotIndexes.h (original)
+++ llvm/trunk/include/llvm/CodeGen/SlotIndexes.h Fri Dec  4 17:00:54 2015
@@ -333,6 +333,8 @@ namespace llvm {
   /// This pass assigns indexes to each instruction.
   class SlotIndexes : public MachineFunctionPass {
   private:
+    // IndexListEntry allocator.
+    BumpPtrAllocator ileAllocator;
 
     typedef ilist<IndexListEntry> IndexList;
     IndexList indexList;
@@ -353,9 +355,6 @@ namespace llvm {
     /// and MBB id.
     SmallVector<IdxMBBPair, 8> idx2MBBMap;
 
-    // IndexListEntry allocator.
-    BumpPtrAllocator ileAllocator;
-
     IndexListEntry* createEntry(MachineInstr *mi, unsigned index) {
       IndexListEntry *entry =
         static_cast<IndexListEntry*>(