On Fri, 21 Jun 2024, Richard Sandiford wrote:
> > This has passed verification in native `powerpc64le-linux-gnu' and
> > `x86_64-linux-gnu' regstraps, as well as with the `alpha-linux-gnu'
> > target. OK to apply and backport to the release branches?
>
> Huh! Nice detective work.
Thank you. It did help that `call_pal 158' or the lack of is so easy to
spot in disassembly or compiler output.
Inspired by Roger Sayle's observation that the use of $0 hard register
pre-reload is uncommon I tried to come up with an RTL test case that I
*might* be able to tweak enough, knowing the nature of the bug, to still
trigger with trunk. For that I backported `print_rtx_function' to 4.1.2.
The output it produced was sufficiently different though from the syntax
now accepted for input it wasn't suitable at all. So I thought I could
perhaps tweak it by hand using output from GCC 15 as a reference.
But that did not work either, GCC 15 cannot accept its own output it
would seem, complaining about integer suffixes across a couple of places:
rwlock-test.i:112:100: error: invalid suffix "B" on integer constant
112 | 32)) [1 MEM[(struct _pthread_descr_struct * *)rwlock_8(D) + 32B]+0 S8
A64])) "rwlock-test.i":84:5 discrim 1)
| ^~~
and most importantly, the asm statement:
rwlock-test.i:53:62: error: expected character `)', found `:'
rwlock-test.i:53:65: note: following context is `37)'
where input is:
(cinsn 18 (set (reg/v:DI $0 [ __self ])
(asm_operands:DI ("call_pal %1") ("=r") 0 [
(const_int 158)
]
[
(asm_input:SI ("i") rwlock-test.i:37)
]
[] rwlock-test.i:37)) "rwlock-test.i":37:58)
and the complaint about the `asm_input' expression, and it's not clear to
me what is expected here. So I have given up.
I guess the RTL parser could be improved, or maybe output produced from
`print_rtx_function' isn't right, I don't know.
> The patch is OK for trunk, thanks. I agree that it's a regression
> from 08a692679fb8. Since it's fixing such a hard-to-diagnose wrong
> code bug, and since it seems very safe, I think it's worth backporting
> to all active branches, after a grace period.
Agreed as to the grace period. I have since additionally run the patch
through `riscv64-linux-gnu' verification and John David Anglin was kind
enough to do so with `hppa-unknown-linux-gnu'.
I have pushed the change to trunk now, thank you for your review.
Maciej
