Re: [PATCH 02/11] tcg: Add tcg_gen_revbit{32,64}

On 7/30/26 23:49, Philippe Mathieu-Daudé wrote:
>> +void tcg_gen_revbit32_i64(TCGv_i64 ret, TCGv_i64 arg, int flags);
>> +void tcg_gen_revbit64_i64(TCGv_i64 ret, TCGv_i64 arg);
> 
> Could the bswap flag be defined once per target?

It is not intended for bswap (or revbit) to have a set interpretation for any target, but 
to be contextually correct for the usage.

For instance, TCG_BSWAP_IZ would generally be only known at the call-site, because of how 
one has prepared the input.  It's usage within s390x follows forced zero-extension:

     C(0xe31f, LRVH,    RXY_a, Z,   0, m2_16u, new, r1_16, rev16, 0)
...
     C(0xe33f, STRVH,   RXY_a, Z,   la2, r1_16u, new, m1_16, rev16, 0)

Annoyingly, s390x should have these memory insns updated to perform the "reversed" 
load/store via MO_BSWAP.

> - output sign-extended (TCG_BSWAP_OS):
> 
>    alpha, hppa, loongarch, m68k, mips, riscv, rx, sh4, tricore
> 
> - output zero-extended (TCG_BSWAP_OZ):
> 
>    arm, avr, hexagon, microblaze, openrisc, ppc, sparc, x86, xtensa

But note that arm uses both OS (aarch32 REVSH) and OZ (aarch64 REV32).


r~