[llvm-dev] Are derived pointers caught by RS4GC?

[Philip Reames via llvm-dev]

Please see my previous email re: rematerialization.  This code appears 
correct and as expected.

Philip

On 7/20/21 11:22 AM, Kavindu Gimhan Zoysa wrote:
> Hi Philip,
>
> It is the same output I got that make sense. But as explained in this 
> example https://llvm.org/docs/Statepoints.html#base-derived-pointers 
> <https://llvm.org/docs/Statepoints.html#base-derived-pointers> (the 
> example available in this section), I thought *%gep *should be 
> included in gc-live operand bundle. Isn't that correct?
>
> Kavindu Gimhan Zoysa,
> BSc(Hons) | ENTC | UoM,
> ATL | WSO2
>
> GitHub <https://github.com/KavinduZoysa> LinkedIn 
> <https://www.linkedin.com/in/kavindu-gimhan-zoysa-85939a122/> Medium 
> <https://medium.com/@kavindugimhanzoysa>
>
>
> On Tue, 20 Jul 2021 at 22:53, Philip Reames <listmail at philipreames.com 
> <mailto:listmail at philipreames.com>> wrote:
>
>     $ ./opt -S llvm-dev.ll -rewrite-statepoints-for-gc
>     ; ModuleID = 'llvm-dev.ll'
>     source_filename = "llvm-dev.ll"
>
>     define void @dummy_func() {
>       ret void
>     }
>
>     define i8 addrspace(1)* @test1(i8 addrspace(1)* %obj) gc
>     "statepoint-example" {
>       %gep = getelementptr i8, i8 addrspace(1)* %obj, i64 20000
>       %statepoint_token = call token (i64, i32, void ()*, i32, i32,
>     ...) @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 2882400000,
>     i32 0, void ()* @dummy_func, i32 0, i32 0, i32 0, i32 0) [
>     "gc-live"(i8 addrspace(1)* %obj) ]
>     *%obj.relocated = call coldcc i8 addrspace(1)*
>     @llvm.experimental.gc.relocate.p1i8(token %statepoint_token, i32
>     0, i32 0) ; (%obj, %obj)*
>     *%gep.remat = getelementptr i8, i8 addrspace(1)* %obj.relocated,
>     i64 20000*
>       %p = getelementptr i8, i8 addrspace(1)* %gep.remat, i64 -20000
>       store i8 2, i8 addrspace(1)* %gep.remat, align 1
>       ret i8 addrspace(1)* %p
>     }
>
>     Works for me.  This output is entirely correct as we relocated the
>     base pointer and then rematerialized the derived pointer
>     afterwards.  This is almost always profitable over directly
>     relocating both obj and derived pointers.
>
>     Philip
>
>     On 7/20/21 7:45 AM, Kavindu Gimhan Zoysa via llvm-dev wrote:
>>
>>         define void @dummy_func() {
>>           ret void
>>         }
>>         define i8 addrspace(1)* @test1(i8 addrspace(1)* %obj) gc
>>         "statepoint-example" {
>>           %gep = getelementptr i8, i8 addrspace(1)* %obj, i64 20000
>>           call void @dummy_func()
>>           %p = getelementptr i8, i8 addrspace(1)* %gep, i64 -20000
>>           store i8 2, i8 addrspace(1)* %gep
>>           ret i8 addrspace(1)* %p
>>         }
>>
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