[llvm] r330826 - [RISCV] Support "call" pseudoinstruction in the MC layer

[Shiva Chen via llvm-commits]

Hi Alex.

Thanks for catching this bug.
I think the issue is RISCV register don't have a prefix like $ in
assembly form and pseudo instruction could have full symbol expression
without %hi or %lo which make the assembly parser ambiguous. So every
pseudo instruction has full symbol expression operand need to handle
this. We may need to address this when we introducing la pseudo
instruction.

Shiva

2018-04-26 1:29 GMT+08:00 Alex Bradbury <asb at asbradbury.org>:
> On 25 April 2018 at 17:24, Alex Bradbury <asb at asbradbury.org> wrote:
>> On 25 April 2018 at 15:18, Shiva Chen via llvm-commits
>> <llvm-commits at lists.llvm.org> wrote:
>>> Author: shiva
>>> Date: Wed Apr 25 07:18:55 2018
>>> New Revision: 330826
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=330826&view=rev
>>> Log:
>>> [RISCV] Support "call" pseudoinstruction in the MC layer
>>>
>>> To do this:
>>> 1. Add PseudoCALLIndirct to match indirect function call.
>>>
>>> 2. Add PseudoCALL to support parsing and print pseudo `call` in assembly
>>>
>>> 3. Expand PseudoCALL to the following form with R_RISCV_CALL relocation type
>>>    while encoding:
>>>         auipc ra, func
>>>         jalr ra, ra, 0
>>>
>>> If we expand PseudoCALL before emitting assembly, we will see auipc and jalr
>>> pair when compile with -S. It's hard for assembly parser to parsing this
>>> pair and identify it's semantic is function call and then insert R_RISCV_CALL
>>> relocation type. Although we could insert R_RISCV_PCREL_HI20 and
>>> R_RISCV_PCREL_LO12_I relocation types instead of R_RISCV_CALL.
>>> Due to RISCV relocation design, auipc and jalr pair only can relax to jal with
>>> R_RISCV_CALL + R_RISCV_RELAX relocation types.
>>>
>>> We expand PseudoCALL as late as encoding(RISCVMCCodeEmitter) instead of before
>>> emitting assembly(RISCVAsmPrinter) because we want to preserve call
>>> pseudoinstruction in assembly code. It's more readable and assembly parser
>>> could identify call assembly and insert R_RISCV_CALL relocation type.
>>
>> I've found this patch has problems with function names that coincide
>> with register names. e.g. `call zero` or `call f0`. In combination
>> with r330827, this leads to compilation failures when -save-temps is
>> used.
>
> Fixed in r330846.
>
> Best,
>
> Alex