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

Thu Oct 27 00:40:02 PDT 2022

xen0n added inline comments.

================
Comment at: llvm/test/CodeGen/LoongArch/ir-instruction/atomic-cmpxchg.ll:201
+; LA64-NEXT:  .LBB6_4:
+; LA64-NEXT:    move $a0, $a3
+; LA64-NEXT:    ret
----------------
gonglingqin wrote:
> xen0n wrote:
> > Okay so my suspicion is confirmed, and the implementation is wrong... the [[ https://llvm.org/docs/LangRef.html#cmpxchg-instruction | result of a strong `cmpxchg` ]] should be 1 if `$a3 == $a1`, and 0 otherwise. It shouldn't be the original value.
> > 
> > Please check if I'm misunderstanding anything...
> > The original value at the location is returned, together with a flag indicating success (true) or failure (false).
> The return values of cmpxchg include {original value, i1}, which is checked in this test case for original value.
> 
> ```
>   %res = extractvalue { i32, i1 } %tmp, 0
>   ret i32 %res
> ```
Ah I see. It's compound. Then how about some more tests checking the `i1` part too?

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

https://reviews.llvm.org/D135948