[PATCH] D127189: [clang][AIX] Add option to control quadword lock free atomics ABI on AIX

[ChenZheng via Phabricator via cfe-commits]

shchenz added a comment.

Thanks for the explanation. I am more clear now about the background.



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Comment at: clang/include/clang/Driver/Options.td:3611
   HelpText<"Enable the default Altivec ABI on AIX (AIX only). Uses only volatile vector registers.">;
+def maix_quadword_atomics : Flag<["-"], "maix64-quadword-atomics">,
+  Group<m_Group>, Flags<[CC1Option]>,
----------------
lkail wrote:
> shchenz wrote:
> > amyk wrote:
> > > Would it be better if we called this `maix64-quadword-atomics` instead? 
> > Do we need to change the backend check below too?
> > ```
> > bool PPCTargetLowering::shouldInlineQuadwordAtomics() const {
> >   // TODO: 16-byte atomic type support for AIX is in progress; we should be able
> >   // to inline 16-byte atomic ops on AIX too in the future.
> >   return Subtarget.isPPC64() &&
> >          (EnableQuadwordAtomics || !Subtarget.getTargetTriple().isOSAIX()) &&
> >          Subtarget.hasQuadwordAtomics();
> > }
> > ```
> We don't need to change this yet. When we are compiling a quadword lock free libatomic, we use options `-mabi=quadword-atomics -mllvm -ppc-quadword-atomics` to enforce generating quadword lock-free code on AIX.
This makes me confuse. We need to two different options to control the frontend and backend behavior?

Is it the final usage? Or we will add a follow up patch to map the backend one to the FE one? IMO finally we only need the driver option `-mabi=quadword-atomics` to control the final code generation for 128 bit atomic operations, right?


================
Comment at: clang/lib/Basic/Targets/PPC.cpp:854
+      HasQuadwordAtomics)
+    MaxAtomicInlineWidth = 128;
 }
----------------
lkail wrote:
> shchenz wrote:
> > Can we set `MaxAtomicInlineWidth` in `PPC64TargetInfo::setMaxAtomicWidth()`? There is a `TODO` there
> The `TODO` marks our roadmap towards enabling quardword lock free atomics on AIX too. Putting adjustment here is implementation reason: we don't context of `LanguageOptions` in `PPC64TargetInfo::PPC64TargetInfo`.
OK, fair enough.


Repository:
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  https://reviews.llvm.org/D127189/new/

https://reviews.llvm.org/D127189