[PATCH, middle-end]: Fix PR middle-end/23831

[Uros Bizjak]

Hello!

This patch fixes i386 target problem, exposed by vectorized multiply
insn patterns. The problem is, that a TImode (128bit) constant is
produced, but target supports only 64bit (DImode) constants.

Proposed patch fixes this problem in middle-end. If requested subreg
mode is wider than 2 * HOST_BITS_PER_WIDE_INT, simply skip
immed_double_const simplifications.

For attached testcase, following asm is produced (-O2 -msse2 -ftree-vectorize):

foo:
	pushl	%ebp
	movl	$bm.1591, %eax
	movdqa	.LC0, %xmm3
	movl	%esp, %ebp
	movl	$bm.1591, %edx
	.p2align 4,,15
.L2:
	movdqa	(%eax), %xmm0
	movdqa	%xmm3, %xmm1
	movdqa	%xmm0, %xmm2
	psrldq	$4, %xmm1
	psrldq	$4, %xmm0
	pmuludq	%xmm3, %xmm2
	pmuludq	%xmm1, %xmm0
	addl	$4, %edx
	pshufd	$8, %xmm2, %xmm2
	pshufd	$8, %xmm0, %xmm0
	punpckldq	%xmm0, %xmm2
	movdqa	%xmm2, (%eax)
	addl	$16, %eax
	cmpl	$bm.1591+16, %edx
	jne	.L2
	popl	%ebp
	ret

Patch is regtested on i686-pc-linux-gnu for c and c++. If patch is OK,
could someone commit it to mainline CVS?

:ADDPATCH middle-end:

2005-09-26  Uros Bizjak  <uros@kss-loka.si>

	PR middle-end/23831
	* simplify-rtx.c (simplify_immed_subreg) [MODE_INT]: Skip
	simplification if elem_bitsize > 2 * HOST_BITS_PER_WIDE_INT

testsuite/ChangeLog:
	
2005-09-26  Uros Bizjak  <uros@kss-loka.si>

	PR middle-end/23831
	* gcc.dg/vect/pr23831.c: New test.

Uros.
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