In perl.git, the branch smoke-me/davem/multideref has been created
<http://perl5.git.perl.org/perl.git/commitdiff/86fb299ac5742ef449edde97135d10ecb8eba194?hp=0000000000000000000000000000000000000000>
at 86fb299ac5742ef449edde97135d10ecb8eba194 (commit)
- Log -----------------------------------------------------------------
commit 86fb299ac5742ef449edde97135d10ecb8eba194
Author: David Mitchell <[email protected]>
Date: Fri Oct 24 16:26:38 2014 +0100
Add OP_MULTIDEREF
This op is an optimisation for any series of one or more array or hash
lookups and dereferences, where the key/index is a simple constant or
package/lexical variable. If the first-level lookup is of a simple
array/hash variable or scalar ref, then that is included in the op too.
So all of the following are replaced with a single op:
$h{foo}
$a[$i]
$a[5][$k][$i]
$r->{$k}
local $a[0][$i]
exists $a[$i]{$k}
delete $h{foo}
while these aren't:
$a[0] already handled by OP_AELEMFAST
$a[$x+1] not a simple index
and these are partially replaced:
(expr)->[0]{$k} the bit following (expr) is replaced
$h{foo}[$x+1][0] the first and third lookups are each done with
a multideref op, while the $x+1 expression and
middle lookup are done by existing add, aelem etc
ops.
Up until now, aggregate dereferencing has been very heavyweight in ops; for
example, $r->[0]{$x} is compiled as:
gv[*r] s
rv2sv sKM/DREFAV,1
rv2av[t2] sKR/1
const[IV 0] s
aelem sKM/DREFHV,2
rv2hv sKR/1
gvsv[*x] s
helem vK/2
When executing this, in addition to the actual calls to av_fetch() and
hv_fetch(), there is a lot of overhead of pushing SVs on and off the
stack, and calling lots of little pp() functions from the runops loop
(each with its potential indirect branch miss).
The multideref op avoids that by running all the code in a loop in a
switch statement. It makes use of the new UNOP_AUX type to hold an array
of
typedef union {
PADOFFSET pad_offset;
SV *sv;
IV iv;
UV uv;
} UNOP_AUX_item;
In something like $a[7][$i]{foo}, the GVs or pad offsets for @a and $i are
stored as items in the array, along with a pointer to a const SV holding
'foo', and the UV 7 is stored directly. Along with this, some UVs are used
to store a sequence of actions (several actions are squeezed into a single
UV).
Then the main body of pp_multideref is a big while loop round a switch,
which reads actions and values from the AUX array. The two big branches in
the switch are ones that are affectively unrolled (/DREFAV, rv2av, aelem)
and (/DREFHV, rv2hv, helem) triplets. The other branches are various entry
points that handle retrieving the different types of initial value; for
example 'my %h; $h{foo}' needs to get %h from the pad, while '(expr)->{foo}'
needs to pop expr off the stack.
Note that there is a slight complication with /DEREF; in the example above
of $r->[0]{$x}, the aelem op is actually
aelem sKM/DREFHV,2
which means that the aelem, after having retrieved a (possibly undef)
value from the array, is responsible for autovivifying it into a hash,
ready for the next op. Similarly, the rv2sv that retrieves $r from the
typeglob is responsible for autovivifying it into an AV. This action
of doing the next op's work for it complicates matters somewhat. Within
pp_multideref, the autovivification action is instead included as the
first step of the current action.
In terms of benchmarking with Porting/bench.pl, a simple lexical
$a[$i][$j] shows a reduction of approx 40% in numbers of instructions
executed, while $r->[0][0][0] uses 54% fewer. The speedup for hash
accesses is relatively more modest, since the actual hash lookup (i.e.
hv_fetch()) is more expensive than an array lookup. A lexical $h{foo}
uses 10% fewer, while $r->{foo}{bar}{baz} uses 34% fewer instructions.
In general, the more lookups done, the bigger the proportionate saving.
M MANIFEST
M Porting/deparse-skips.txt
M dist/Safe/t/safeops.t
M dump.c
M embed.fnc
M embed.h
M embedvar.h
M ext/B/B.xs
M ext/B/B/Concise.pm
M ext/B/t/OptreeCheck.pm
M ext/B/t/concise-xs.t
M ext/B/t/f_sort.t
M ext/Opcode/Opcode.pm
M intrpvar.h
M lib/B/Deparse.pm
M lib/B/Deparse.t
M lib/B/Op_private.pm
M op.c
M op.h
M opcode.h
M opnames.h
M perl.h
M pp.c
M pp_hot.c
M pp_proto.h
M proto.h
M regen/op_private
M regen/opcodes
M sv.c
M t/lib/warnings/9uninit
A t/op/multideref.t
M t/op/svleak.t
M t/perf/benchmarks
M t/perf/opcount.t
commit 89c226f8fc01beb036c0f9b89a5a3dc2141d4e82
Author: David Mitchell <[email protected]>
Date: Mon Oct 27 17:33:32 2014 +0000
add UNOP_AUX OP class
This is the same as a UNOP, but with the addition of an op_aux field,
which points to an array of UNOP_AUX_item unions.
It is intended as a general escape mechanism for adding per-op-type extra
fields (or arrays of items) to UNOPs.
Its class character (for regen/opcodes etc) is '+'.
Currently there are no ops of this type; but shortly, OP_MULTIDEREF will
be added, which is the original motivation for this new op type.
M embed.fnc
M embed.h
M ext/B/B.pm
M ext/B/B.xs
M ext/B/B/Concise.pm
M op.c
M op.h
M perl.h
M proto.h
M regen/op_private
M regen/opcode.pl
M regen/opcodes
commit 3b147eba3971b9574efd8d3756f09d3b29fdd6af
Author: David Mitchell <[email protected]>
Date: Sun Nov 2 16:01:00 2014 +0000
ext/B/Makefile.PL: spot hex defines
The regex in ext/B/Makefile.PL was failing to find C constants of the
form
#define FOO 0xNNN
where NNN contained one or more [a-fA-F] chars
With this change it imports a few more constants:
CXTYPEMASK
GVf_IMPORTED
RV2CVOPCV_FLAG_MASK
OPpARG4_MASK
OPpPADRANGE_COUNTMASK
M ext/B/Makefile.PL
commit c34b0e6937523e801dc8355e047e7570c3b9cf41
Author: David Mitchell <[email protected]>
Date: Thu Oct 30 10:28:06 2014 +0000
Perl_op_sibling_splice(): update OPf_KIDS
Previously this function didn't update OPf_KIDS when altering the
children. This was only safe as long as the count of kids didn't transition
between 0 and !0.
M op.c
commit 3ceff5fdf05da2c11b7853b4a44bb3d5be93b0f8
Author: David Mitchell <[email protected]>
Date: Fri Oct 24 16:23:38 2014 +0100
add S_deb_padvar() to dump.c
factor out the code that prints a pad var name in -Dt output
M dump.c
commit 3587d24479e53bee45cff6aac8065f4edb512889
Author: David Mitchell <[email protected]>
Date: Thu Aug 7 16:34:23 2014 +0100
add S_op_clear_gv() to op.c
Abstract out the code that clear an GV attached to an op,
since we will shortly need to do this in more than one place
M op.c
commit 3799409cf62fbb98376af93d2f69f453f78b5108
Author: David Mitchell <[email protected]>
Date: Sun Jul 27 20:59:48 2014 +0100
create S_check_hash_fields() function
factor out the code in S_finalize_op() that performs checks on hash keys
into a separate function, since we'll shortly need to call this code from
more than one place.
M op.c
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