* the options given when GCC was configured/built;

Configured with: /home/niva/src/gcc-3.4-binutils/configure
--with-headers=/home/vxuser/oc2000/mips/src/include
--without-libs --enable-generated-files-in-srcdir
--enable-threads=posix -with-dwarf2 --disable-shared
--target=mips64-none-elf --verbose --enable-checking
--enable-languages=c --srcdir=/home/niva/svnwork/src
--prefix=/home/niva/local1 --enable-cpp

     * the complete command line that triggers the bug;

./mips64-none-elf-gcc -O1 -G 0 -mips1 -mabi=32 .c -c -save-temps

     * the compiler output (error messages, warnings, etc.);

No error messages

     * the  preprocessed  file (*.i*)

struct s {
  unsigned long long a:8, b:32;
};

struct s
f(struct s x)
{
  x.b = 0xcdef1234;
  return x;
}

main()
{
  static struct s i;
  i.a = 12;
  i = f(i);
  if (i.b != 0xcdef1234)
    abort();
  exit(0);
}


     * the resultant assembler code is

	.file	1 "930126-2.c"
	.section .mdebug.abi32
	.previous
	.text
	.align	2
	.globl	f
	.ent	f
f:
	.frame	$sp,0,$31		# vars= 0, regs= 0/0, args= 0, gp= 0
	.mask	0x00000000,0
	.fmask	0x00000000,0
	.set	noreorder
	.set	nomacro
	
	move	$2,$4
	li	$3,-16777216			# 0xffffffffff000000
	and	$6,$6,$3
	li	$3,13434880			# 0xcd0000
	ori	$3,$3,0xef12
	or	$6,$6,$3
	li	$3,16711680			# 0xff0000
	ori	$3,$3,0xffff
	and	$7,$7,$3
	li	$3,872415232			# 0x34000000
	or	$7,$7,$3
	sw	$7,4($4)
	j	$31
	sw	$6,0($4)

	.set	macro
	.set	reorder
	.end	f

	.lcomm	i.0,8
	.align	2
	.globl	main
	.ent	main
main:
	.frame	$sp,32,$31		# vars= 0, regs= 4/0, args= 16, gp= 0
	.mask	0x800d0000,-4
	.fmask	0x00000000,0
	.set	noreorder
	.set	nomacro
	
	addiu	$sp,$sp,-32
	sw	$31,28($sp)
	sw	$19,24($sp)
	sw	$18,20($sp)
	sw	$16,16($sp)
	lui	$16,%hi(i.0)
	li	$2,12
	sb	$2,%lo(i.0)($16)
	lw	$7,%lo(i.0+4)($16)
	lw	$6,%lo(i.0)($16)
	jal	f
	addiu	$4,$16,%lo(i.0)

	addiu	$3,$16,%lo(i.0+1)
	lwl	$2,%lo(i.0+1)($16)
	move	$19,$2
	lwr	$19,3($3)
	move	$4,$0
	bne	$4,$0,$L4
	li	$2,-839974912			# 0xffffffffcdef0000

	ori	$2,$2,0x1234
	beq	$19,$2,$L3
	nop

$L4:
	jal	abort
	nop

$L3:
	jal	exit
	move	$4,$0

	.set	macro
	.set	reorder
	.end	main

     * the error here is that there is no NOP between LWL and
       the next command that uses the output register of LWL:

	lwl	$2,%lo(i.0+1)($16)
	move	$19,$2

     * As a result, the test ends with jump to abort. When I
       insert the NOP manually to the assembler code, the test
       passes OK.