------- Comment #7 from vmakarov at redhat dot com 2009-04-24 15:53 -------
In gcc4.4 we have before reg-stack.c
(insn 96 82 97 4 /home/vmakarov/build/bb.ii:8 (parallel [
(set (mem/c:SI (plus:SI (reg/f:SI 7 sp)
(const_int 28 [0x1c])) [0 S4 A32])
(fix:SI (reg:DF 9 st(1))))
(clobber (reg:XF 9 st(1)))
]) 119 {fix_truncsi_i387_fisttp} (expr_list:REG_DEAD (reg:DF 9 st(1))
(nil)))
in subst_stack_regs first it is changed to
(insn:TI 96 82 97 4 /home/vmakarov/build/bb.ii:8 (parallel [
(set (mem/c:SI (plus:SI (reg/f:SI 7 sp)
(const_int 28 [0x1c])) [0 S4 A32])
(fix:SI (reg:DF 8 st)))
(clobber (reg:XF 9 st(1)))
]) 119 {fix_truncsi_i387_fisttp} (expr_list:REG_DEAD (reg:DF 8 st)
(nil)))
Then it is trying to change clobber and fail because there is no note
about dead or unused reg 9, it fails in subst_stack_regs_pat on the
assert:
if (note)
emit_pop_insn (insn, regstack, *dest, EMIT_BEFORE);
else
{
note = find_reg_note (insn, REG_UNUSED, *dest);
gcc_assert (note);
}
The gcc4.3 has analogous insn before reg-stack.c
(insn 106 92 107 4 bb.ii:8 (parallel [
(set (mem/c:SI (plus:SI (reg/f:SI 7 sp)
(const_int 28 [0x1c])) [0 S4 A8])
(fix:SI (reg:DF 11 st(3))))
(clobber (reg:XF 11 st(3)))
]) 159 {fix_truncsi_i387_fisttp} (expr_list:REG_DEAD (reg:DF 11 st(3))
(expr_list:REG_UNUSED (reg:XF 11 st(3))
(nil))))
The difference is in presense of REG_UNUSED (reg:XF 11 st(3)) which
does not permit the gcc_assert aborts gcc4.3. The note is present
because LR_OUT at BB 4 does not contain 11 st(3). Quite opposite, 9
st(1) is in LR_OUT at BB 4 in gcc4.4. Therefore REG_UNUSED note is
not generated for gcc4.4.
So why there is such difference in LR_OUT for 4.3 vs 4.4? Gcc4.3 is
lucky to use 11 st (3) only in BB3 (where insn 116 is placed). Gcc4.4
uses 9 st(1) in insn 96 and reuses it in many other BBs. Because of
partially set register for variable R, we got that LR_OUT is set up in
BB 3. If somebody is interesting here is the CFG with LR_OUT & LR_IN
and usage of 9 st (1):
0
|
v
2-->
| |
v |
3->| lr_out:9 set 9;use 9;clobber 9
| |
v |
4 | lr_out:9 call
| |
v |
5<- lr_in:9 lr_out:9
|\
| \
6->| lr_out:9 set 9
| |
| |
7 | lr_in:9 lr_out:9 use 9 .. set 9
| |
| |
8<- lr_in:9 lr_out:9
|\
| \
9 | lr_in:9 use 9
| |
| |
10<-
So the code
if (note)
emit_pop_insn (insn, regstack, *dest, EMIT_BEFORE);
else
{
note = find_reg_note (insn, REG_UNUSED, *dest);
gcc_assert (note);
}
does not take situation of reusage of hard register for partially set
variable.
IMHO, the code should be
Index: reg-stack.c
===================================================================
--- reg-stack.c (revision 146648)
+++ reg-stack.c (working copy)
@@ -1381,11 +1381,9 @@ subst_stack_regs_pat (rtx insn, stack re
if (note)
emit_pop_insn (insn, regstack, *dest, EMIT_BEFORE);
else
- {
- note = find_reg_note (insn, REG_UNUSED, *dest);
- gcc_assert (note);
- }
- remove_note (insn, note);
+ note = find_reg_note (insn, REG_UNUSED, *dest);
+ if (note)
+ remove_note (insn, note);
replace_reg (dest, FIRST_STACK_REG + 1);
}
else
I'll send the patch soon.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39856
