Re: Fix PR optimization/7520

["Eric Botcazou" <ebotcazou at libertysurf dot fr>]

> I mean this.  Clobbering a register does not give it a new value.

Ok, I was probably thinking more of the register in itself than of the value
it has to carry.

So the flow2 pass has the right to inconditionally put its REG_DEAD note
here:

(insn 96 37 38 1 (nil) (set (reg:SI 0 eax)
        (reg:SI 3 ebx)) 38 {*movsi_1} (insn_list 98 (nil))
    (nil))

(insn:HI 38 96 39 1 0x40188814 (parallel [
            (set (reg:CCZ 17 flags)
                (compare:CCZ (ior:SI (reg:SI 0 eax)
                        (reg:SI 2 ecx [61]))
                    (const_int 0 [0x0])))
            (clobber (reg:SI 0 eax))
        ]) 217 {*iorsi_3} (insn_list 97 (insn_list 96 (nil)))
    (expr_list:REG_DEAD (reg:SI 0 eax)
        (nil)))

regardless of what follows, in particular:

;; End of basic block 1, registers live:
 0 [ax] 2 [cx] 3 [bx] 6 [bp] 7 [sp] 16 [] 20 [frame]  ?

That's a bit counter-intuitive.

--
Eric Botcazou