efriedma added inline comments.
================
Comment at: clang/lib/Basic/Targets/Sparc.cpp:224
+ Builder.defineMacro("__GCC_HAVE_SYNC_COMPARE_AND_SWAP_8");
+ }
}
----------------
ro wrote:
> efriedma wrote:
> > ro wrote:
> > > efriedma wrote:
> > > > This probably should be refactored so the target-independent code
> > > > generates it based on MaxAtomicInlineWidth, instead of duplicating it
> > > > for each target. But I guess you don't need to do that here.
> > > >
> > > > From the other code, the `getCPUGeneration(CPU) == CG_V9` check should
> > > > only guard the definition of __GCC_HAVE_SYNC_COMPARE_AND_SWAP_8?
> > > > This probably should be refactored so the target-independent code
> > > > generates it based on MaxAtomicInlineWidth, instead of duplicating it
> > > > for each target. But I guess you don't need to do that here.
> > >
> > > Good: one issue at a time ;-)
> > >
> > > > From the other code, the `getCPUGeneration(CPU) == CG_V9` check should
> > > > only guard the definition of __GCC_HAVE_SYNC_COMPARE_AND_SWAP_8?
> > >
> > > I don't think so: at least `gcc` defines none of the four with `-m32
> > > -mcpu=v8` and all with `-m32 -mcpu=v9`.
> > This code, the code that sets MaxAtomicInlineWidth, and the code
> > inSPARCISelLowering.cpp that calls setMaxAtomicSizeInBitsSupported() all
> > need to agree about the supported atomic operations.
> >
> > I guess the current setting of MaxAtomicInlineWidth is wrong?
> I'd say so, yes: gcc -m32 inlines ops on `_Atomic long long` while `clang-11
> -m32 -mcpu=v9` doesn't.
Oh, hmm, it looks like the backend's support for 32-bit v9 is really limited;
we basically generate v8 code, with a couple limited exceptions. Probably okay
to make clang assume 64-bit atomics are actually supported, even if we don't
inline the implementation at the moment; they should still behave correctly.
I was more wondering about what we do for v8: we set MaxAtomicInlineWidth to
32, but I don't think it supports atomic cmpxchg at all.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D86621/new/
https://reviews.llvm.org/D86621
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