> -----Original Message-----
> From: Alan Modra [mailto:amo...@gmail.com]
> On Wed, Feb 17, 2016 at 06:31:45AM -0600, Segher Boessenkool wrote:
> > > (gdb) p debug_rtx (other_insn)
> > > (insn 11 10 16 2 (set (reg:SI 165 [ D.2339+-3 ])
> > > (if_then_else:SI (ne (reg:CC 166)
> > > (const_int 0 [0]))
> > > (reg:SI 168)
> > > (reg:SI 167))) test.c:7 317 {isel_unsigned_si}
> > > (expr_list:REG_DEAD (reg:SI 168)
> > > (expr_list:REG_DEAD (reg:SI 167)
> > > (expr_list:REG_DEAD (reg:CC 166)
> > > (expr_list:REG_EQUAL (gtu:SI (reg:CC 166)
> > > (const_int 0 [0]))
> > > (nil))))))
> >
> > The REG_EQUAL there is bad already. Where does that come from?
>
> Rohit explain that quite well already, I thought. It's there due to
> transforming a GTU to NE in another insn, which means the reg mode
> combine changes to CCmode via rs6000.h:SELECT_CC_MODE.
Yes, when the reg mode (reg:166) changes while transforming a GTU to NE,
it affects the reg mode of all reg:166 in the corresponding REG_NOTE's too.
This is the actual code which changes the mode:
File: combine.c [function: simplify_set (Line No 6604)]
#ifndef HAVE_cc0
....
if (compare_mode != GET_MODE (dest))
{
if (can_change_dest_mode (dest, 0, compare_mode))
{
.....
if (regno < FIRST_PSEUDO_REGISTER)
new_dest = gen_rtx_REG (compare_mode, regno);
else
{
SUBST_MODE (regno_reg_rtx[regno], compare_mode);---->(A)
new_dest = regno_reg_rtx[regno];
}
....
}
#endif /* cc0 */
#endif /* SELECT_CC_MODE */
/* If the code changed, we have to build a new comparison in
undobuf.other_insn. */
if (new_code != old_code)
{
int other_changed_previously = other_changed;
unsigned HOST_WIDE_INT mask;
rtx old_cc_use = *cc_use;
SUBST (*cc_use, gen_rtx_fmt_ee (new_code, GET_MODE (*cc_use),
dest, const0_rtx));
---------->(B)
other_changed = 1;
....
Content of 'other_insn' before executing (A)
(gdb) p debug_rtx (other_insn)
(insn 11 10 16 2 (set (reg:SI 165 [ D.2339+-3 ])
(if_then_else:SI (gtu (reg:CCUNS 166)
(const_int 0 [0]))
(reg:SI 168)
(reg:SI 167))) test.c:7 317 {isel_unsigned_si}
(expr_list:REG_DEAD (reg:SI 168)
(expr_list:REG_DEAD (reg:SI 167)
(expr_list:REG_DEAD (reg:CCUNS 166)
(expr_list:REG_EQUAL (gtu:SI (reg:CCUNS 166)
(const_int 0 [0]))
(nil))))))
$26 = void
Content of 'other_insn' after executing (A)
(gdb) p debug_rtx (other_insn)
(insn 11 10 16 2 (set (reg:SI 165 [ D.2339+-3 ])
(if_then_else:SI (gtu (reg:CC 166)
(const_int 0 [0]))
(reg:SI 168)
(reg:SI 167))) test.c:7 317 {isel_unsigned_si}
(expr_list:REG_DEAD (reg:SI 168)
(expr_list:REG_DEAD (reg:SI 167)
(expr_list:REG_DEAD (reg:CC 166)
(expr_list:REG_EQUAL (gtu:SI (reg:CC 166)
(const_int 0 [0]))
(nil))))))
Content of 'other_insn' after executing (B)
gdb) p debug_rtx (other_insn)
(insn 11 10 16 2 (set (reg:SI 165 [ D.2339+-3 ])
(if_then_else:SI (ne (reg:CC 166)
(const_int 0 [0]))
(reg:SI 168)
(reg:SI 167))) test.c:7 317 {isel_unsigned_si}
(expr_list:REG_DEAD (reg:SI 168)
(expr_list:REG_DEAD (reg:SI 167)
(expr_list:REG_DEAD (reg:CC 166)
(expr_list:REG_EQUAL (gtu:SI (reg:CC 166)
(const_int 0 [0]))
(nil))))))
Regards,
Rohit
