[PATCH] D99487: [CodeGen] Port basic block sections from ELF to COFF

Tue Apr 20 00:07:59 PDT 2021

TaoPan added a comment.

In D99487#2698978 <https://reviews.llvm.org/D99487#2698978>, @tmsriram wrote:

>> Would you be able to paste the entire assembly with cv loc directives?  I can try to take a look.

As the entire assembly has 500 lines, I sent to you through mail, I'll do if you think paste part of them or entire assembly to here is better.

>> Basically, this means your code won't assemble with CFI and that is a serious limitation. This is similar to what we did for ELF.  All CFI directives should be within a cfi_startproc  cfi_endproc directive as part of a single section. When you fragment a function into multiple sections, this breaks.  We solved this by adding a separate startproc endproc directive for each section.
>>
>> I have some suggestions for you to better understand the problem:
>>
>> - GCC supports function splitting with -freorder-blocks-and-partition.  You can use GCC to split a function and see what it does to cv_loc directives.
>> - D79978 <https://reviews.llvm.org/D79978>  is what we did with ELF, my guess is it is very similar.  You just need to add a startproc endproc to every function and duplicate all the information to compute Call Frame Address.
>
> https://llvm.org/docs/Extensions.html#codeview-dependent
>
> These aren't the CFI directives and I falsely assumed that.  Stems from my misunderstanding of COFF, please take a note of this.

Thanks for your detail guidance! It's very helpful. I'll study what you did with ELF and codeview format.

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