i386: Add alternate representation for {and,or,xor}b %ah,%dh.

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.
See also PR target/78904.

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])))

2023-06-24  Roger Sayle  <roger@nextmovesoftware.com>

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

diff --git a/gcc/config/i386/i386.md b/gcc/config/i386/i386.md
index 95a6653cd13e20b5527bd3d38186dab1fa50d5bc..b50d82bf768385bf11bca7327d12d57fe1269a2a 100644 (file)
--- a/gcc/config/i386/i386.md
+++ b/gcc/config/i386/i386.md
@@ -11380,6 +11380,8 @@
   [(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
@@ -12092,6 +12094,26 @@
   [(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