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

[Kavindu Gimhan Zoysa via llvm-dev]

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 (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>
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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