Re: [x86 PATCH] Fix issue with x86_64_const_vector_operand predicate.

[Uros Bizjak <ubizjak@gmail.com>]

On Sat, Jul 16, 2022 at 2:06 PM Roger Sayle <roger@nextmovesoftware.com> wrote:
>
>
> This patch fixes (what I believe is) a latent bug in i386.md's
> x86_64_const_vector_operand define_predicate.  According to the
> documentation, when a predicate is called with rtx operand OP and
> machine_mode operand MODE, we can't shouldn't assume that the
> MODE is (or has been checked to be) GET_MODE (OP).
>
> The failure mode is that recog can call x86_64_const_vector_operand
> on an arbitrary CONST_VECTOR passing a MODE of V2QI_mode, but when
> the CONST_VECTOR is in fact V1TImode, it's unsafe to directly call
> ix86_convert_const_vector_to_integer, which assumes that the CONST_VECTOR
> contains CONST_INTs when it actually contains CONST_WIDE_INTs.  The
> checks in this define_predicate need to be testing OP's mode, and
> ideally confirming that this matches the passed in/specified MODE.
>
> This bug is currently latent, but adding an innocent/unrelated
> define_insn, such as "(set (reg:CCC FLAGS_REG) (const_int 0))" to
> i386.md can occasionally change the order in which genrecog generates
> its tests, then ICEing during bootstrap due to V1TI CONST_VECTORs.
>
>
> This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
> and make -k check, both with and without --target-board=unix{-m32},
> with no new failures.  Ok for mainline?
>
> 2022-07-16  Roger Sayle  <roger@nextmovesoftware.com>
>
> gcc/ChangeLog
>         * config/i386/predicates.md (x86_64_const_vector_operand):
>         Check the operand's mode matches the specified mode argument.

OK.

Thanks,
Uros.

>
>
> Thanks in advance,
> Roger
> --
>