Re: libcall problem during new unroller merge

[Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>]

Hello,

> > during merging new loop unroller, I have encountered the following
> > problem (masked on rtlopt branch by other pass):
> > 
> > Consider loop in that strcmp is called; it is translated into rtl as
> > 
> > (insn 542 541 543 (nil) (set (reg:SI 236)
> >         (mem/s/u:SI (plus:SI (reg:SI 235)
> >                 (reg:SI 231)) [9 <variable>.name+0 S4 A32])) -1 (nil)
> >     (nil))
> > 
> > (insn 543 542 544 (nil) (set (mem/f:SI (plus:SI (reg/f:SI 56 virtual-outgoing-args)
> >                 (const_int 4 [0x4])) [0 S4 A32])
> >         (reg:SI 236)) -1 (nil)
> >     (insn_list:REG_LIBCALL 547 (nil)))
> > 
> > (insn 544 543 545 (nil) (set (reg:SI 237)
> >         (mem/f:SI (symbol_ref:SI ("ix86_cpu_string")) [9 ix86_cpu_string+0 S4 A32])) -1 (nil)
> >     (nil))
> > 
> > (insn 545 544 546 (nil) (set (mem/f:SI (reg/f:SI 56 virtual-outgoing-args) [0 S4 A32])
> >         (reg:SI 237)) -1 (nil)
> >     (nil))
> > 
> > (call_insn/u 546 545 547 (nil) (set (reg:SI 0 eax)
> >         (call (mem:QI (symbol_ref:SI ("strcmp")) [0 S1 A8])
> >             (const_int 8 [0x8]))) -1 (nil)
> >     (expr_list:REG_EH_REGION (const_int -1 [0xffffffff])
> >         (nil))
> >     (expr_list (use (mem:BLK (scratch) [0 A8]))
> >         (nil)))
> > 
> > (insn 547 546 548 (nil) (set (reg:SI 238)
> >         (reg:SI 0 eax)) -1 (nil)
> >     (insn_list:REG_RETVAL 543 (expr_list:REG_EQUAL (expr_list (use (mem:BLK (scratch) [0 A8]))
> >                 (expr_list (symbol_ref:SI ("strcmp"))
> >                     (expr_list (mem/f:SI (symbol_ref:SI ("ix86_cpu_string")) [9 ix86_cpu_string+0 S4 A32])
> >                         (expr_list (mem/s/u:SI (plus:SI (reg:SI 235)
> >                                     (reg:SI 231)) [9 <variable>.name+0 S4 A32])
> >                             (nil)))))
> >             (nil))))

one question to this -- what does the expr_list inside REG_EQUAL mean?
>From the documentation I've got feeling that there should be rtl
expression of value of libcall; is this some way to express that this
is call to function with those arguments that is not documented?
Anyway, it makes delete_trivially_dead_insns wrong, as it does not
find register usage in this REG_EQUAL note.

Zdenek