> It would really help if you could provide testcases which show the
> suboptimal code and any analysis you've done.
I tried introducing a define_subst pattern that substitutes something
one of two other subst patterns already changed.
The first subst pattern helps remove a superfluous and on the shift
count operand by accepting both variants, with and without an and for
the insn pattern.
(define_subst "masked_op_subst"
[(set (match_operand:DSI 0 "" "")
(shift:DSI (match_operand:DSI 1 "" "")
(match_operand:SI 2 "" "")))]
""
[(set (match_dup 0)
(shift:DSI (match_dup 1)
(and:SI (match_dup 2)
(match_operand:SI 3 "const_int_6bitset_operand" "jm6"))))])
The second subst helps encode a shift count addition like $r1 + 1 as
address style operand 1($r1) that is directly supported by the shift
instruction.
(define_subst "addr_style_op_subst"
[(set (match_operand:DSI_VI 0 "" "")
(shift:DSI_VI (match_operand:DSI_VI 1 "" "")
(match_operand:SI 2 "" "")))]
""
[(set (match_dup 0)
(shift:DSI_VI (match_dup 1)
(plus:SI (match_operand:SI 2 "register_operand" "a")
(match_operand 3 "const_int_operand" "n"))))])
Both of these are also used in combination.
Now, in order to get rid of the subregs in the pattern combine creates,
I would need to be able to do something like
(define_subst "subreg_subst"
[(set (match_operand:DI 0 "" "")
(shift:DI (match_operand:DI 1 "" "")
(subreg:SI (match_dup:DI 2)))]
where the (match_dup:DI 2) would capture both (and:SI ...) [with the
first argument being either a register or an already substituted
(plus:SI ...)] as well as a simple (plus:SI ...).
As far as I can tell match_dup:mode can be used to change the mode of
the top-level operation but the operands will remain the same. For
this, a match_dup_deep or whatever would be useful. I'm pretty sure we
don't want to open this can of worms, though :)
To get rid of this, I explicitly duplicated all three subst combinations
resulting in a lot of additional code. This is not necessary when the
subregs are eliminated by the middle end via SHIFT_COUNT_TRUNCATED.
Maybe there is a much more obvious way that I missed?
Regards
Robin
