[llvm-commits] [llvm] r162733 - in /llvm/trunk: include/llvm/CodeGen/SelectionDAGNodes.h include/llvm/Target/TargetSelectionDAG.td lib/CodeGen/SelectionDAG/SelectionDAG.cpp test/CodeGen/Hexagon/newvaluejump.ll test/CodeGen/Hexagon/newvaluestore.l

[Hal Finkel]

On Wed, 29 Aug 2012 13:52:05 -0700
Jakob Stoklund Olesen <stoklund at 2pi.dk> wrote:

> 
> On Aug 29, 2012, at 11:45 AM, Eli Friedman <eli.friedman at gmail.com>
> wrote:
> 
> >> +  unsigned Flags = MachineMemOperand::MOVolatile;
> >> +  if (Opcode != ISD::ATOMIC_STORE)
> >> +    Flags |= MachineMemOperand::MOLoad;
> >> +  if (Opcode != ISD::ATOMIC_LOAD)
> >> +    Flags |= MachineMemOperand::MOStore;
> > 
> > I'm not sure this is safe; I suppose it depends on how exactly
> > "volatile" is defined, though.  Specifically, it's unsafe to move an
> > arbitrary load from after an "acquire" load to before it.
> 
> OK, r162857 should bring us back to the old behavior.
> 
> MachineInstr::isSafeToMove() now treats volatile and atomic loads as
> if they were 'stores'. Here, 'store' means a barrier for moving a
> load instruction.

Should these semantics be documented somewhere in the language
reference?

 -Hal

> 
> Thanks, Eli
> 
> /jakob
> 
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-- 
Hal Finkel
Postdoctoral Appointee
Leadership Computing Facility
Argonne National Laboratory