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

[Philip Reames via llvm-dev]

$ ./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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