https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106419
--- Comment #9 from Kewen Lin <linkw at gcc dot gnu.org> ---
(In reply to Segher Boessenkool from comment #8)
> So for which pseudo and which hard register did this ICE, and what did the
> code look like at that point?
The culprit pseudo is r133, the values of those related expressions in the
check:
lra_reg_info[i].nrefs -> 4
reg_renumber[i] -> 97
overlaps_hard_reg_set_p(lra_reg_info[i].conflict_hard_regs, E_SImode, 97) ->
true
Before IRA, the code looks like:
(note 21 1 166 2 [bb 2] NOTE_INSN_BASIC_BLOCK)
(insn 166 21 2 2 (set (reg:SI 229)
(reg:SI 3 3 [ foo ])) "test.f":1:23 562 {*movsi_internal1}
(expr_list:REG_DEAD (reg:SI 3 3 [ foo ])
(nil)))
(insn 2 166 167 2 (set (reg/v/f:SI 133 [ foo ])
(reg:SI 229)) "test.f":1:23 562 {*movsi_internal1}
(expr_list:REG_DEAD (reg:SI 229)
(nil)))
....
(insn 33 32 34 4 (set (reg:SI 3 3)
(reg/v/f:SI 137 [ g ])) "test.f":17:72 562 {*movsi_internal1}
(nil))
(insn 34 33 35 4 (set (reg:SI 97 ctr)
(reg/v/f:SI 133 [ foo ])) "test.f":17:72 562 {*movsi_internal1}
(nil))
(call_insn 35 34 38 4 (parallel [
(call (mem:SI (reg:SI 97 ctr) [0 *foo_21(D) S4 A8])
(const_int 0 [0]))
(use (const_int 4 [0x4]))
(clobber (reg:SI 96 lr))
]) "test.f":17:72 814 {*call_indirect_nonlocal_sysvsi}
(expr_list:REG_DEAD (reg:SI 97 ctr)
(expr_list:REG_DEAD (reg:SI 3 3)
(nil)))
(expr_list:SI (use (reg:SI 3 3))
(nil)))
...
in IRA, the hard reg assignment is:
125:r120 l0 9 86:r125 l0 10 13:r126 l0 29 87:r127 l0 8
73:r128 l0 44 35:r133 l0 3 33:r134 l0 4 31:r135 l0 0
...
choosing r3 for r133. As above, the r3 is redefined at insn 33, r133 is used
in insn34, so it has to try to split the live range of r133.
I didn't dig into LRA code, I don't really understand what the condition means.
:( The reason why I did the hacking by commenting gcc_unreachable() is to see
how it causes some unexpected consequence without this kind of checking. As
shown above, the resulted assembly looks inefficient, but it should work from
correctness perspective. So I guessed maybe the condition is too strict or we
miss to consider something special and punt some valid things.
