x86: Always return pseudo register in ix86_gen_scratch_sse_rtx

x86: Always return pseudo register in ix86_gen_scratch_sse_rtx

ix86_gen_scratch_sse_rtx returns XMM7/XMM15/XMM31 as a scratch vector
register to prevent RTL optimizers from removing vector register.  It
introduces a conflict with explicit XMM7/XMM15/XMM31 usage and when it
is called by RTL optimizers, it may introduce conflicting usages of
XMM7/XMM15/XMM31.

Change ix86_gen_scratch_sse_rtx to always return a pseudo register and
xfail x86 tests which are optimized with a hard scratch register.

gcc/

	PR target/104704
	* config/i386/i386.cc (ix86_gen_scratch_sse_rtx): Always return
	a pseudo register.

gcc/testsuite/

	PR target/104704
	* gcc.target/i386/incoming-11.c: Xfail.
	* gcc.target/i386/pieces-memset-3.c: Likewise.
	* gcc.target/i386/pieces-memset-37.c: Likewise.
	* gcc.target/i386/pieces-memset-39.c: Likewise.
	* gcc.target/i386/pieces-memset-46.c: Likewise.
	* gcc.target/i386/pieces-memset-47.c: Likewise.
	* gcc.target/i386/pieces-memset-48.c: Likewise.
	* gcc.target/i386/pr90773-5.c: Likewise.
	* gcc.target/i386/pr90773-14.c: Likewise.
	* gcc.target/i386/pr90773-17.c: Likewise.
	* gcc.target/i386/pr100865-8a.c: Likewise.
	* gcc.target/i386/pr100865-8c.c: Likewise.
	* gcc.target/i386/pr100865-9c.c: Likewise.
	* gcc.target/i386/pieces-memset-21.c: Always expect vzeroupper.
	* gcc.target/i386/pr82941-1.c: Likewise.
	* gcc.target/i386/pr82942-1.c: Likewise.
	* gcc.target/i386/pr82990-1.c: Likewise.
	* gcc.target/i386/pr82990-3.c: Likewise.
	* gcc.target/i386/pr82990-5.c: Likewise.
	* gcc.target/i386/pr100865-11b.c: Expect vmovdqa instead of
	vmovdqa64.
	* gcc.target/i386/pr100865-12b.c: Likewise.
	* gcc.target/i386/pr100865-8b.c: Likewise.
	* gcc.target/i386/pr100865-9b.c: Likewise.
	* gcc.target/i386/pr104704-1.c: New test.
	* gcc.target/i386/pr104704-2.c: Likewise.
	* gcc.target/i386/pr104704-3.c: Likewise.
	* gcc.target/i386/pr104704-4.c: Likewise.
	* gcc.target/i386/pr104704-5.c: Likewise.
	* gcc.target/i386/pr104704-6.c: Likewise.