Re: [PATCH] RISC-V: fix TARGET_PROMOTE_FUNCTION_MODE hook for libcalls

[Jeff Law <jeffreyalaw@gmail.com>]

On 10/31/23 17:41, Palmer Dabbelt wrote:
> On Tue, 31 Oct 2023 16:18:35 PDT (-0700), jeffreyalaw@gmail.com wrote:
>>
>>
>> On 10/31/23 12:35, Vineet Gupta wrote:
>>> riscv_promote_function_mode doesn't promote a SI to DI for libcalls
>>> case.
>>>
>>> The fix is what generic promote_mode () in explow.cc does. I really
>>> don't understand why the old code didn't work, but stepping thru the
>>> debugger shows old code didn't and fixed does.
>>>
>>> This showed up when testing Ajit's REE ABI extension series which probes
>>> the ABI (using a NULL tree type) and ends up hitting the libcall code 
>>> path.
>>>
>>> [Usual caveat, I'll wait for Pre-commit CI to run the tests and report]
>>>
>>> gcc/ChangeLog:
>>>     * config/riscv/riscv.cc (riscv_promote_function_mode): Fix mode
>>>       returned for libcall case.
>> Hmm.  There may be dragons in here.  I'll need to find and review an old
>> conversation in this space (libcalls and argument promotions).
> 
> We also have a non-orthogonality in the ABI sign extension rules between 
> SI and DI, a few of us were talking about it on the internal slack 
> (though the specifics were for a different patch, Vineet has a few in 
> flight).
So the old issue I was thinking of really only affects targets that push 
arguments on the stack and when a sub-word push actually allocates a 
full word on the stack (m68k, but !coldfire, h8 and probably others of 
that era).

Point being, those issues don't apply here.

jeff