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

[Alex Bradbury via llvm-commits]

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