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.


Thanks in advance,
Roger
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