[PATCH] D135948: [LoongArch] Add codegen support for cmpxchg on LA64

Thu Oct 27 04:56:31 PDT 2022

gonglingqin added inline comments.

================
Comment at: llvm/test/CodeGen/LoongArch/ir-instruction/atomic-cmpxchg.ll:326
+; LA64-NEXT:  .LBB10_4:
+; LA64-NEXT:    bstrpick.d $a0, $a1, 31, 0
+; LA64-NEXT:    xor $a0, $a3, $a0
----------------
xen0n wrote:
> This seems wrong: the following `xor` insn responsible for the `same value -> 0` part operates on full GRLen, but here `a1` i.e. `%cmp` gets zero-extended to `a0`, yet `a3` i.e. the value from memory is loaded with `ll.w` that sign-extends. I expect this will fail for cases where `cmp == *ptr && cmp < 0`.
> 
> Either this should be a sign-extension, or the comparison shouldn't be `xor`.
Thanks for the fact checking! I will fix it.

Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D135948/new/

https://reviews.llvm.org/D135948