[llvm-dev] Stackmap offset computation on AArch64

[Philip Reames via llvm-dev]

Looking at PrologEpilogInserter and searching for STATEPOINT is a a good 
starting point.

Philip

On 7/27/19 2:22 AM, Sam Elliott via llvm-dev wrote:
> I think you should be looking in AArch64FrameLowering.cpp. The relevant function is AArch64FrameLowering::getFrameIndexReference, I believe.
>
> Sam
>
>> On 26 Jul 2019, at 10:55AM, Loïc Ottet via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>>
>> Hi all,
>>
>> I am trying to implement statepoints for the AArch64 target and I’m running into the issue where the following bitcode:
>>
>> define i32 addrspace(1)* @test(i32 addrspace(1)* %ptr) gc "statepoint-example" {
>> entry:
>>   call token (i64, i32, i1 ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_i1f(i64 0, i32 0, i1 ()* @foo, i32 0, i32 0, i32 0, i32 0, i32 addrspace(1)* %ptr)
>>   ret i32 addrspace(1)* %ptr
>> }
>>
>> This gets emitted as the following assembly code:
>>
>> test:                                   // @test
>> 	.cfi_startproc
>> // %bb.0:                               // %entry
>> 	str	x30, [sp, #-16]!        // 8-byte Folded Spill
>> 	.cfi_def_cfa_offset 16
>> 	.cfi_offset w30, -16
>> 	str	x0, [sp, #8]
>> 	bl	return_i1
>> .Ltmp0:
>> 	ldr	x0, [sp, #8]
>> 	ldr	x30, [sp], #16          // 8-byte Folded Reload
>> 	ret
>> .Lfunc_end0:
>> 	.size	test, .Lfunc_end0-test
>> 	.cfi_endproc
>>
>> The generated stackmap indicates that %ptr is located at offset -8 from the stack pointer, instead of the expected 8. After trying a few other configurations it happens that the offsets are computed relative to the stack pointer of the parent frame instead of the current one.
>>
>> Can someone point me to the place where the stackmap offsets get computed so I can try to debug this?
>>
>> Thanks,
>>
>> Loïc Ottet
>> _______________________________________________
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>> llvm-dev at lists.llvm.org
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> --
> Sam Elliott
> Software Developer - LLVM
> lowRISC CIC
> selliott at lowrisc.org
> --
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