rnk added inline comments.
================
Comment at: lib/CodeGen/CGBuiltin.cpp:3003
+ case Builtin::BI_InterlockedCompareExchangePointer:
+ case Builtin::BI_InterlockedCompareExchangePointer_nf: {
llvm::Type *RTy;
----------------
mgrang wrote:
> rnk wrote:
> > Is the no fence version really equivalent to this seq_cst version here?
> I don't see InterlockedCompareExchangePointer creating a fence but it should.
> (since it is the fence version). So maybe that needs to be fixed (and
> possibly other fence functions).
>
> InterlockedCompareExchangePointer_nf should not create a fence so the current
> implementation seems correct.
Hm, if we're supposed to have fences, we're probably missing them everywhere. I
thought the atomicrmw orderings were enough, but that shows what I know about
the C++ memory model. =p
We don't generate a fence for this intrinsic when MSVC does:
```
unsigned char test_arm(long *base, long idx) {
return _interlockedbittestandreset_acq(base, idx);
}
```
@efriedma, is MSVC over-emitting extra fences, or are we under-emitting? If
this is their "bug", should we be bug-for-bug compatible with it so we get the
same observable memory states?
Repository:
rC Clang
https://reviews.llvm.org/D52807
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