PR target/113690: Remove TImode REG_EQUAL notes in STV.

PR target/113690: Remove TImode REG_EQUAL notes in STV.

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 or delete the
attached REG_EQUAL note.  This implements Uros' recommendation of removing
these notes.  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

2024-02-07  Roger Sayle  <roger@nextmovesoftware.com>
	    Uros Bizjak  <ubizjak@gmail.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): Delete REG_EQUAL notes.
	Use timode_convert_cst.

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