MIPS: Trouble with address calculation near the useg/kseg boundary

[Paul Koning <paul_koning at dell dot com>]

I'm running into a crash caused by mishandling of address calculation of an array element address when that array is near the bottom of kseg0 (0xffffffff80000000).

The code essentially does this
	foo = v[i - 2].elem;
where i is current zero.

Assume for now the negative array offset is valid -- data structure elements in question exist to both sides of the label "v".

The generated code looks like this:

	/* i is in v0 */
	addiu	v0, -2
	sll	v0, 3
	lui	v1, 0x8000
	addu	v0, v1
	lbu	a1, 7110(v0)

What's going on here is that &v[0].elem is 0xfffffffff80007110.  The reference is valid -- array elements are 8 bytes so element -2 is still in kseg0.

However, the addu produces value 0000000007ffffff0 in v0 -- the result of adding -16 to the 32 bit value 0x800000000.  

Given that I have an ABI with 64 bit registers -- even though it has 32 bit pointers -- I would say the address adjustment should have been done with daddu; if that had been done I would have gotten the correct address.

GCC is 4.5.1, NetBSD target.

	paul