On Sat, Jun 07, 2025 at 11:38:46AM +0100, Stafford Horne wrote:
> On Fri, Jun 06, 2025 at 09:54:53PM +0100, Stafford Horne wrote:
> > On Fri, Jun 06, 2025 at 11:31:00PM +0300, Dimitar Dimitrov wrote:
> > > On Fri, Jun 06, 2025 at 06:12:13PM +0100, Stafford Horne wrote:
> > > > On Fri, Jun 06, 2025 at 04:41:21PM +0100, Stafford Horne wrote:
> > > > > On Fri, Jun 06, 2025 at 04:20:10PM +0100, Richard Sandiford wrote:
> > > > > > Stafford Horne <sho...@gmail.com> writes:
> > > > > > > Hello,
> > > > > > >
> > > > > > > This seems to be causing a build regression on the or1k port.
> > > > > > >
> > > > > > > I have not quite figured it out yet but I have bisected to this
> > > > > > > commit.
> > > > > > >
> > > > > > > The failure is as below, this seems to be caused by the cstoresi4
> > > > > > > instruction produced by
> > > > > > > or1k.md. So I think its likely something we are doing funny in
> > > > > > > the port.
> > > > > > >
> > > > > > > Thanks to Jeff for pointing this out. If you have any idea let
> > > > > > > me know.
> > > > > > >
> > > > > > > Log:
> > > > > > >
> > > > > > > during RTL pass: ce1
> > > > > > > dump file: libgcc2.c.286r.ce1
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/libgcc/libgcc2.c: In
> > > > > > > function '__muldi3':
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/libgcc/libgcc2.c:538:1:
> > > > > > > internal compiler error: in emit_move_multi_word, at expr.cc:4492
> > > > > > > 538 | }
> > > > > > > | ^
> > > > > > > 0x1b094df internal_error(char const*, ...)
> > > > > > >
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/gcc/diagnostic-global-context.cc:517
> > > > > > > 0x6459c1 fancy_abort(char const*, int, char const*)
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/gcc/diagnostic.cc:1815
> > > > > > > 0x473a2e emit_move_multi_word
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/gcc/expr.cc:4492
> > > > > > > 0x93fd7d emit_move_insn(rtx_def*, rtx_def*)
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/gcc/expr.cc:4746
> > > > > > > 0x9175f1 copy_to_reg(rtx_def*)
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/gcc/explow.cc:630
> > > > > > > 0xd18977 gen_lowpart_general(machine_mode, rtx_def*)
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/gcc/rtlhooks.cc:56
> > > > > > > 0x9414c7 convert_mode_scalar
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/gcc/expr.cc:818
> > > > > > > 0x9421a1 convert_modes(machine_mode, machine_mode, rtx_def*,
> > > > > > > int)
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/gcc/expr.cc:961
> > > > > > > 0xc0afa0 prepare_operand(insn_code, rtx_def*, int,
> > > > > > > machine_mode, machine_mode, int)
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/gcc/optabs.cc:4637
> > > > > > > 0xc0b33a prepare_cmp_insn
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/gcc/optabs.cc:4538
> > > > > > > 0xc0f0dd emit_conditional_move(rtx_def*, rtx_comparison,
> > > > > > > rtx_def*, rtx_def*, machine_mode, int)
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/gcc/optabs.cc:5098
> > > > > > > 0x192cc7b noce_emit_cmove
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/gcc/ifcvt.cc:1777
> > > > > > > 0x193365b try_emit_cmove_seq
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/gcc/ifcvt.cc:3410
> > > > > > > 0x193365b noce_convert_multiple_sets_1
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/gcc/ifcvt.cc:3705
> > > > > > > 0x1933c71 noce_convert_multiple_sets
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/gcc/ifcvt.cc:3496
> > > > > > > 0x1938687 noce_process_if_block
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/gcc/ifcvt.cc:4045
> > > > > > > 0x1938687 noce_find_if_block
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/gcc/ifcvt.cc:4726
> > > > > > > 0x1938687 find_if_header
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/gcc/ifcvt.cc:4931
> > > > > > > 0x1938687 if_convert
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/gcc/ifcvt.cc:6078
> > > > > > > 0x1938d01 rest_of_handle_if_conversion
> > > > > > > /home/shorne/work/gnu-toolchain/gcc/gcc/ifcvt.cc:6143
> > > > > > >
> > > > > > > -Stafford
> > > > > >
> > > > > > Can you attach the .i?
> > > > >
> > > > > Sure please find attached, I can reproduce with the or1k compiler
> > > > > using:
> > > > >
> > > > > $HOME/work/gnu-toolchain/build-gcc/./gcc/cc1 -O2 __muldi3.i
> > > > >
> > > > > I am still debugging, but I notice when reverting the patch the
> > > > > compiler never
> > > > > goes to emit_move_multi_word(). I am trying to work backwards as to
> > > > > where it goes
> > > > > different, it's just taking a bit of time as I haven't debugged GCC
> > > > > ICE's for a
> > > > > while.
> > > >
> > > > I made some progress on this. In openRISC we generate cstoresi4 with
> > > > special
> > > > register SR_F (condition flag) bit register.
> > > >
> > > > This is represented as (reg:BI 34 ?sr_f).
> > > >
> > > > The RTL produced for cstoresi4 becomes something like:
> > > >
> > > > // The compare
> > > > (insn 49 48 50 (set (reg:BI 34 ?sr_f)
> > > > (leu:BI (reg/v:SI 68 [ __x2D.6783 ])
> > > > (reg/v:SI 69 [ __x1D.6782 ])))
> > > > "/home/shorne/work/gnu-toolchain/gcc/libgcc/libgcc2.c":532:22 -1
> > > > (nil)
> > > > // The conditional branch
> > > > (jump_insn 50 49 0 (set (pc)
> > > > (if_then_else (ne (reg:BI 34 ?sr_f)
> > > > (const_int 0 [0]))
> > > > (label_ref 0)
> > > > (pc)))
> > > > "/home/shorne/work/gnu-toolchain/gcc/libgcc/libgcc2.c":532:22 -1
> > > > (int_list:REG_BR_PROB 536870916 (nil)))
> > > >
> > > > During ce1 the try_emit_cmove_seq would try to convert (reg:BI 34
> > > > ?sr_f) to SI.
> > > > Before this patch it was done in gen_lowpart_general by
> > > > simplify_context::simplify_gen_subreg.
> > > >
> > > > The simplity to subreg operation would convert:
> > > > (reg:BI 34 ?sr_f)
> > > >
> > > > To:
> > > > (subreg:SI (reg:BI 34 ?sr_f) 0)
> > > >
> > > > But now the call to validate_subreg is returning false and
> > > > simplify_gen_subreg
> > > > returns NULL_RTX, this causes gen_lowpart_general to try to do
> > > > copy_to_reg,
> > > > which fails.
> > > >
> > > > I need to step away for a bit, but I would next look into why
> > > > validate_subreg
> > > > is now failing to allow (reg:BI 34 ?sr_f) to be subreg'd.
> > >
> > > I think that the REG_CAN_CHANGE_MODE_P call in validate_subreg is
> > > rejecting the subreg, because or1k_can_change_mode_class rejects the
> > > mode change of sr_f from BI to SI.
> > >
> > Hi Dimitar,
> >
> > That's right, I noticed the same thing and I am testing out a patch to
> > or1k_can_change_mode_class now, it fixes the ICE. But I'll have to spend a
> > bit
> > more time testing.
>
> Hi All,
>
> The patch I have now is as below and it looks to work ok:
>
> --- a/gcc/config/or1k/or1k.cc
> +++ b/gcc/config/or1k/or1k.cc
> @@ -1408,8 +1408,9 @@ static bool
> or1k_can_change_mode_class (machine_mode from, machine_mode to,
> reg_class_t rclass)
> {
> + /* Allow cnoverting special flags to SI mode subregs. */
> if (rclass == FLAG_REGS)
> - return from == to;
> + return from == to || (from == BImode && to == SImode);
> return true;
> }
Another patch I intend to merge tomorrow will tighten the checks even
more: https://gcc.gnu.org/pipermail/gcc-patches/2025-June/685837.html
Seeing that or1k_hard_regno_mode_ok forbids SImode for class FLAG_REGS,
the validate_subreg may once again start rejecting subregs for or1k.
Regards,
Dimitar
>
> I just wanted to make some notes here as originally I and Jeff thought it was
> the cstore* pattern causing the issue. But it was the cbranch* pattern. If I
> have anything wrong please let me know.
>
> I haven't touched this stuff for a while, but it's slowly coming back.
>
> The RTL that was having problems was:
>
> ;; expand cbranchsi4
> (insn 20 19 21 2 (set (reg:BI 34 ?sr_f)
> (leu:BI (reg/v:SI 68 [ __x2 ])
> (reg/v:SI 69 [ __x1 ])))
> "/home/shorne/work/gnu-toolchain/gcc/libgcc/libgcc2.c":535:20 -1
> (nil))
> (jump_insn 21 20 22 2 (set (pc) ;;
> (if_then_else (ne (reg:BI 34 ?sr_f) ;; <-- pairs with "*cbranch"
> (const_int 0 [0])) ;;
> (label_ref 25) ;;
> (pc)))
> "/home/shorne/work/gnu-toolchain/gcc/libgcc/libgcc2.c":535:20 -1
> (int_list:REG_BR_PROB 536870916 (nil))
> -> 25)
>
> In ce1 (if-conversion) try_emit_cmove_seq tries to convert (ne (reg:BI 34
> ?sr_f)
> (const_int 0 [0])) to cmove.
>
> The conversion results in:
>
> (insn 70 0 71 (set (reg:SI 110)
> (ashift:SI (subreg:SI (reg:BI 34 ?sr_f) 0)
> (const_int 31 [0x1f]))) -1
> (nil))
>
> After this after this another sequence is also generated, cost analysis is
> done
> and both sequences are discarded.
>
> My patch restores the original behavior which allows the subreg conversion to
> be
> valid again.
>
> ## Note on cstoresi4 and PUT_MODE.
>
> There was some concern raised by Jeff about the use of PUT_MODE in cstoresi4.
> This is here to convert a 'ne' to 'ne:SI', for example, allowing the generated
> RTL to match with the "*scc" insn pattern later.
>
> It seems to be working OK so I will leave this as is for now. But if you have
> any suggestions let me know.
>
> ;; cstoresi4 from or1k.md
>
> (define_expand "cstoresi4"
> [(set (match_operand:SI 0 "register_operand" "")
> (if_then_else:SI
> (match_operator 1 "comparison_operator"
> [(match_operand:SI 2 "reg_or_0_operand" "")
> (match_operand:SI 3 "reg_or_s16_operand" "")])
> (match_dup 0)
> (const_int 0)))]
> ""
> {
> or1k_expand_compare (operands + 1);
> PUT_MODE (operands[1], SImode);
> emit_insn (gen_rtx_SET (operands[0], operands[1]));
> DONE;
> })
>
> ;; Example expanded cstoresi4
> (insn 9 8 10 2 (set (reg:BI 34 ?sr_f)
> (ne:BI (reg:SI 48 [ _13 ])
> (reg:SI 55)))
> "/home/shorne/work/gnu-toolchain/gcc/libgcc/libgcc2.c":68:52 -1
> (nil))
> (insn 10 9 11 2 (set (reg:SI 54 [ _2+-3 ])
> (ne:SI (reg:BI 34 ?sr_f) <-- PUT_MODE -> pair with "*scc"
> (const_int 0 [0])))
> "/home/shorne/work/gnu-toolchain/gcc/libgcc/libgcc2.c":68:52 -1
> (nil))
>
> -Stafford
