[PATCH] D86621: [clang][Sparc] Default to -mcpu=v9 for SparcV8 on Solaris

[Eli Friedman via Phabricator via cfe-commits]

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:
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  https://reviews.llvm.org/D86621/new/

https://reviews.llvm.org/D86621