This patch fixes PR target/113690, an ICE-on-valid regression on x86_64
that exhibits with a specific combination of command line options.  The
cause is that x86's scalar-to-vector pass converts a chain of instructions
from TImode to V1TImode, but fails to appropriately update the attached
REG_EQUAL note.  Given that multiplication isn't supported in V1TImode,
the REG_NOTE handling code wasn't expecting to see a MULT.  Easily solved
with additional handling for other binary operators that may potentially
(in future) have an immediate constant as the second operand that needs
handling.  For convenience, this code (re)factors the logic to convert
a TImode constant into a V1TImode constant vector into a subroutine and
reuses it.

For the record, STV is actually doing something useful in this strange
testcase,  GCC with -O2 -fno-dce -fno-forward-propagate
-fno-split-wide-types
-funroll-loops generates:

foo:    movl    $v, %eax
        pxor    %xmm0, %xmm0
        movaps  %xmm0, 48(%rax)
        movaps  %xmm0, (%rax)
        movaps  %xmm0, 16(%rax)
        movaps  %xmm0, 32(%rax)
        ret

With the addition of -mno-stv (to disable the patched code) it gives:

foo:    movl    $v, %eax
        movq    $0, 48(%rax)
        movq    $0, 56(%rax)
        movq    $0, (%rax)
        movq    $0, 8(%rax)
        movq    $0, 16(%rax)
        movq    $0, 24(%rax)
        movq    $0, 32(%rax)
        movq    $0, 40(%rax)
        ret


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?


2024-02-05  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
        PR target/113690
        * config/i386/i386-features.cc (timode_convert_cst): New helper
        function to convert a TImode CONST_SCALAR_INT_P to a V1TImode
        CONST_VECTOR.
        (timode_scalar_chain::convert_op): Use timode_convert_cst.
        (timode_scalar_chain::convert_insn): If a REG_EQUAL note contains
        a binary operator where the second operand is an immediate integer
        constant, convert it to V1TImode using timode_convert_cst.
        Use timode_convert_cst.

gcc/testsuite/ChangeLog
        PR target/113690
        * gcc.target/i386/pr113690.c: New test case.


Thanks in advance,
Roger
--