Richard Sandiford wrote:
> Also, you need to beware of cases in which operands[1] overlaps
> operands[0]. The splitter says:
>
> [(set (match_dup 2) (match_dup 4))
> (set (match_dup 3) (match_dup 5))]
>
> and operands[2] is always the highpart:
>
> operands[2] = gen_highpart(QImode, operands[0]);
>
> but consider the case in which operands[1] (and thus operands[4])
> is a memory reference that uses the high part of operands[0] as
> a base register. In that case, the base register will be modified
> by the first split instruction and have the wrong value in the
> second split instruction. See other ports for the canonical way
> of handling this.
>
> Richard
By looking at other ports, I learned that I can detect when this happens
by using the reg_overlap_mentioned_p(). Here is one case:
(insn 43 115 74 (set (reg:HI 7 %i0h)
(mem/s/j:HI (plus:HI (reg/f:HI 7 %i0h [orig:39 source ] [39])
(const_int 2 [0x2])) [0 <variable>.r+0 S2 A8])) 3
{*movhi} (nil)
(nil))
I need to tell the compiler not to use as destination the same base
register when doing index operations. Any suggestions on how do I that?
Thanks for your help.
-Omar
