Problem when computing memory dependencies for scheduling pass1

["Amker.Cheng" <amker dot cheng at gmail dot com>]

Hi all:
   I have found something strange when scheduling instructions.
considering following piece of code:
-------------------------------------------------c start
int func(float x)
{
  int r = 0;
  r = (*(unsigned int*)&x) >> 23;
  return r;
}
-------------------------------------------------c end

the return value is different when compiling with or without optimization.
Have tested on 4.2.4 and 4.3.3 on mips, 4.3.2(ubuntu) on x86 and
results are the same.
Is this a bug, or something wrong with the example code?

following is output for mips target, hope it can help.

commands:
mipsel-elf-gcc -march=mips1 -EL -G0 -mabi=32 -S test/dummy.c -o
test/dummy.S -fdump-rtl-all -fsched-verbose=9 -v -O2


the as output is :
-------------------------------------------------as start
	.section .mdebug.abi32
	.previous
	.text
	.align	2
	.globl	func
	.ent	func
func:
	.frame	$sp,0,$31		# vars= 0, regs= 0/0, args= 0, gp= 0
	.mask	0x00000000,0
	.fmask	0x00000000,0
	.set	noreorder
	.set	nomacro
	
	lw	$2,0($sp)
	sw	$4,0($sp)
	j	$31
	srl	$2,$2,23

	.set	macro
	.set	reorder
	.end	func
	.size	func, .-func
	.ident	"GCC: (GNU) 4.2.4"
--------------------------------------------------as end
it seems the load insn is scheduled before store, which resulting in
using of uninitialized data.

following is the dumped rtls before and after sched1:

before sched1:
---------------------------------------------------

(note 8 2 6 2 [bb 2] NOTE_INSN_BASIC_BLOCK)

(insn 6 8 7 2 (set (mem/c/i:SF (reg/f:SI 77 $arg) [3 x+0 S4 A32])
        (reg:SF 4 $4 [ x ])) 233 {*movsf_softfloat} (nil)
    (expr_list:REG_DEAD (reg:SF 4 $4 [ x ])
        (nil)))

(note 7 6 12 2 NOTE_INSN_FUNCTION_BEG)

(insn 12 7 13 2 (set (reg:SI 196)
        (mem:SI (reg/f:SI 77 $arg) [4 S4 A32])) 213 {*movsi_internal} (nil)
    (nil))
-----------------------------------------------------

after sched1:
---------------------------------------------------
    (insn 12 17 6 2 (set (reg:SI 196)
            (mem:SI (reg/f:SI 77 $arg) [4 S4 A32])) 213 {*movsi_internal} (nil)
        (nil))

    (insn 6 12 20 2 (set (mem/c/i:SF (reg/f:SI 77 $arg) [3 x+0 S4 A32])
            (reg:SF 4 $4 [ x ])) 233 {*movsf_softfloat} (nil)
        (expr_list:REG_DEAD (reg:SF 4 $4 [ x ])
            (nil)))
-----------------------------------------------------

have checked gcc's source, It seems the two mem operands in insn12 and insn6
is computed into two different alias sets, so maybe this problem have
something to do with
the force type cast?

The result is very strange, so please help and any comments will be
highly appreciated.

-- 
Best Regards.