[PATCH] D151312: [PowerPC][AIX] Enable quadword atomics by default for AIX

[Hubert Tong via Phabricator via llvm-commits]

hubert.reinterpretcast added inline comments.


================
Comment at: llvm/lib/Target/PowerPC/PPCISelLowering.cpp:18411
 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()) &&
+  return Subtarget.isPPC64() && EnableQuadwordAtomics &&
          Subtarget.hasQuadwordAtomics();
----------------
lkail wrote:
> hubert.reinterpretcast wrote:
> > lkail wrote:
> > > hubert.reinterpretcast wrote:
> > > > With this, turning off `EnableQuadwordAtomics` will have an effect for non-AIX platforms. I think this function should be left alone (except for updating the comment to say that the ability to turn off quadword atomics for AIX is a historical artifact).
> > > That's a good point. Will update the comment.
> > I meant that perhaps the functionality should be left the same as before? Otherwise, the scope of the patch is bigger than necessary (and tests may need expansion).
> Is it still necessary to keep `EnableQuadwordAtomics`(and defaults to `true`) for AIX? Since the updated libatomic is already delivered, I don't see the essentiality to keep it.
It is my understanding that the minimum requirements for the `libatomic` that has lock-free quadword atomics enabled is the same as that for Clang/LLVM on AIX in general, right? I would then agree that we may not need `EnableQuadwordAtomics` anymore; however, I think the patch here should update the LLVM release notes to indicate what version of the `libatomic` library in required.

If I am not mistaken, the `libatomic` functionality that is needed is (at least currently) available only as part of the (redistributable) IBM Open XL runtimes.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D151312/new/

https://reviews.llvm.org/D151312