[x86 PATCH] Add alternate representation for {and,or,xor}b %ah,%dh.

[x86 PATCH] Add alternate representation for {and,or,xor}b %ah,%dh.

[Roger Sayle]

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A patch that I'm working on to improve RTL simplifications in the
middle-end results in the regression of pr78904-1b.c, due to changes in
the canonical representation of high-byte (%ah, %bh, %ch, %dh) logic.
This patch avoids/prevents those failures by adding support for the
alternate representation, duplicating the existing *<code>qi_ext<mode>_2
as *<code>qi_ext<mode>_3 (the new version also replacing any_or with
any_logic to provide *andqi_ext<mode>_3 in the same pattern).  Removing
the original pattern isn't trivial, as it's generated by define_split,
but this can be investigated after the other pieces are approved.

The current representation of this instruction is:

(set (zero_extract:DI (reg/v:DI 87 [ aD.2763 ])
        (const_int 8 [0x8])
        (const_int 8 [0x8]))
    (subreg:DI (xor:QI (subreg:QI (zero_extract:DI (reg:DI 94)
                    (const_int 8 [0x8])
                    (const_int 8 [0x8])) 0)
            (subreg:QI (zero_extract:DI (reg/v:DI 87 [ aD.2763 ])
                    (const_int 8 [0x8])
                    (const_int 8 [0x8])) 0)) 0))

after my proposed middle-end improvement, we attempt to recognize:

(set (zero_extract:DI (reg/v:DI 87 [ aD.2763 ])
        (const_int 8 [0x8])
        (const_int 8 [0x8]))
    (zero_extract:DI (xor:DI (reg:DI 94)
            (reg/v:DI 87 [ aD.2763 ]))
        (const_int 8 [0x8])
        (const_int 8 [0x8])))

This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
and make -k check, both with and without --target_board=unix{-m32}
with no new failures.  Ok for mainline?


2023-06-18  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
        * config/i386/i386.md (*<code>qi_ext<mode>_3): New define_insn.


Thanks in advance,
Roger
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diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 0929115..889405e 100644
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -10848,6 +10848,8 @@
   [(set_attr "type" "alu")
    (set_attr "mode" "QI")])
 
+;; *andqi_ext<mode>_3 is defined via *<code>qi_ext<mode>_3 below.
+
 ;; Convert wide AND instructions with immediate operand to shorter QImode
 ;; equivalents when possible.
 ;; Don't do the splitting with memory operands, since it introduces risk
@@ -11560,6 +11562,26 @@
   [(set_attr "type" "alu")
    (set_attr "mode" "QI")])
 
+(define_insn "*<code>qi_ext<mode>_3"
+  [(set (zero_extract:SWI248
+	  (match_operand 0 "int248_register_operand" "+Q")
+	  (const_int 8)
+	  (const_int 8))
+	(zero_extract:SWI248
+	  (any_logic:SWI248
+	    (match_operand 1 "int248_register_operand" "%0")
+	    (match_operand 2 "int248_register_operand" "Q"))
+	  (const_int 8)
+	  (const_int 8)))
+   (clobber (reg:CC FLAGS_REG))]
+  "(!TARGET_PARTIAL_REG_STALL || optimize_function_for_size_p (cfun))
+   /* FIXME: without this LRA can't reload this pattern, see PR82524.  */
+   && (rtx_equal_p (operands[0], operands[1])
+       || rtx_equal_p (operands[0], operands[2]))"
+  "<logic>{b}\t{%h2, %h0|%h0, %h2}"
+  [(set_attr "type" "alu")
+   (set_attr "mode" "QI")])
+
 ;; Convert wide OR instructions with immediate operand to shorter QImode
 ;; equivalents when possible.
 ;; Don't do the splitting with memory operands, since it introduces risk

Re: [x86 PATCH] Add alternate representation for {and,or,xor}b %ah,%dh.

[Uros Bizjak]

On Sun, Jun 18, 2023 at 11:35 AM Roger Sayle <roger@nextmovesoftware.com> wrote:
>
>
> A patch that I'm working on to improve RTL simplifications in the
> middle-end results in the regression of pr78904-1b.c, due to changes in
> the canonical representation of high-byte (%ah, %bh, %ch, %dh) logic.
> This patch avoids/prevents those failures by adding support for the
> alternate representation, duplicating the existing *<code>qi_ext<mode>_2
> as *<code>qi_ext<mode>_3 (the new version also replacing any_or with
> any_logic to provide *andqi_ext<mode>_3 in the same pattern).  Removing
> the original pattern isn't trivial, as it's generated by define_split,
> but this can be investigated after the other pieces are approved.

IIRC, I have added these patterns to please combine, based on what
combine generates for the above mentioned testcases. I believe there
is no canonical representation of high-byte logic, so these patterns
are what was appropriate at the time. So, yes, a canonical
representation is the way to go.

Also, please note PR82524. I have a solution for this, we need a
define and split to perform some additional copy of a non-matched
register (there is one pattern that does that in i386.md, but
considering that these patterns are not that common and are rarely
used, I left others as they are).
>
> The current representation of this instruction is:
>
> (set (zero_extract:DI (reg/v:DI 87 [ aD.2763 ])
>         (const_int 8 [0x8])
>         (const_int 8 [0x8]))
>     (subreg:DI (xor:QI (subreg:QI (zero_extract:DI (reg:DI 94)
>                     (const_int 8 [0x8])
>                     (const_int 8 [0x8])) 0)
>             (subreg:QI (zero_extract:DI (reg/v:DI 87 [ aD.2763 ])
>                     (const_int 8 [0x8])
>                     (const_int 8 [0x8])) 0)) 0))
>
> after my proposed middle-end improvement, we attempt to recognize:
>
> (set (zero_extract:DI (reg/v:DI 87 [ aD.2763 ])
>         (const_int 8 [0x8])
>         (const_int 8 [0x8]))
>     (zero_extract:DI (xor:DI (reg:DI 94)
>             (reg/v:DI 87 [ aD.2763 ]))
>         (const_int 8 [0x8])
>         (const_int 8 [0x8])))
>
> This patch has been tested on x86_64-pc-linux-gnu with make bootstrap
> and make -k check, both with and without --target_board=unix{-m32}
> with no new failures.  Ok for mainline?

I would rather commit this fix after the regression happens. The patch
regresses relatively rarely used simplification, and scan-asm
regressions are not that critical. So, OK for mainline, but after the
regression happens, and it will be clear what patch fixes.

Thanks,
Uros.

>
>
> 2023-06-18  Roger Sayle  <roger@nextmovesoftware.com>
>
> gcc/ChangeLog
>         * config/i386/i386.md (*<code>qi_ext<mode>_3): New define_insn.
>
>
> Thanks in advance,
> Roger
> --
>