return ret;
}
-/*
- Helper function for newASSIGNOP to detect commonality between the
- lhs and the rhs. (It is actually called very indirectly. newASSIGNOP
- flags the op and the peephole optimizer calls this helper function
- if the flag is set.) Marks all variables with PL_generation. If it
- returns TRUE the assignment must be able to handle common variables.
-
- PL_generation sorcery:
- An assignment like ($a,$b) = ($c,$d) is easier than
- ($a,$b) = ($c,$a), since there is no need for temporary vars.
- To detect whether there are common vars, the global var
- PL_generation is incremented for each assign op we compile.
- Then, while compiling the assign op, we run through all the
- variables on both sides of the assignment, setting a spare slot
- in each of them to PL_generation. If any of them already have
- that value, we know we've got commonality. Also, if the
- generation number is already set to PERL_INT_MAX, then
- the variable is involved in aliasing, so we also have
- potential commonality in that case. We could use a
- single bit marker, but then we'd have to make 2 passes, first
- to clear the flag, then to test and set it. And that
- wouldn't help with aliasing, either. To find somewhere
- to store these values, evil chicanery is done with SvUVX().
-*/
-PERL_STATIC_INLINE bool
-S_aassign_common_vars(pTHX_ OP* o)
-{
- OP *curop;
- for (curop = cUNOPo->op_first; curop; curop = OpSIBLING(curop)) {
- if (PL_opargs[curop->op_type] & OA_DANGEROUS) {
- if (curop->op_type == OP_GV || curop->op_type == OP_GVSV
- || curop->op_type == OP_AELEMFAST) {
- GV *gv = cGVOPx_gv(curop);
- if (gv == PL_defgv
- || (int)GvASSIGN_GENERATION(gv) == PL_generation)
- return TRUE;
- GvASSIGN_GENERATION_set(gv, PL_generation);
- }
- else if (curop->op_type == OP_PADSV ||
- curop->op_type == OP_PADAV ||
- curop->op_type == OP_PADHV ||
- curop->op_type == OP_AELEMFAST_LEX ||
- curop->op_type == OP_PADANY)
- {
- padcheck:
- if (PAD_COMPNAME_GEN(curop->op_targ)
- == (STRLEN)PL_generation
- || PAD_COMPNAME_GEN(curop->op_targ) == PERL_INT_MAX)
- return TRUE;
- PAD_COMPNAME_GEN_set(curop->op_targ, PL_generation);
-
- }
- else if (curop->op_type == OP_RV2CV)
- return TRUE;
- else if (curop->op_type == OP_RV2SV ||
- curop->op_type == OP_RV2AV ||
- curop->op_type == OP_RV2HV ||
- curop->op_type == OP_RV2GV) {
- if (cUNOPx(curop)->op_first->op_type != OP_GV) /* funny deref? */
- return TRUE;
- }
- else if (curop->op_type == OP_PUSHRE) {
- GV *const gv =
-#ifdef USE_ITHREADS
- ((PMOP*)curop)->op_pmreplrootu.op_pmtargetoff
- ? MUTABLE_GV(PAD_SVl(((PMOP*)curop)->op_pmreplrootu.op_pmtargetoff))
- : NULL;
-#else
- ((PMOP*)curop)->op_pmreplrootu.op_pmtargetgv;
-#endif
- if (gv) {
- if (gv == PL_defgv
- || (int)GvASSIGN_GENERATION(gv) == PL_generation)
- return TRUE;
- GvASSIGN_GENERATION_set(gv, PL_generation);
- }
- else if (curop->op_targ)
- goto padcheck;
- }
- else if (curop->op_type == OP_PADRANGE)
- /* Ignore padrange; checking its siblings is sufficient. */
- continue;
- else
- return TRUE;
- }
- else if (PL_opargs[curop->op_type] & OA_TARGLEX
- && curop->op_private & OPpTARGET_MY)
- goto padcheck;
-
- if (curop->op_flags & OPf_KIDS) {
- if (aassign_common_vars(curop))
- return TRUE;
- }
- }
- return FALSE;
-}
-
-/* This variant only handles lexical aliases. It is called when
- newASSIGNOP decides that we don’t have any common vars, as lexical ali-
- ases trump that decision. */
-PERL_STATIC_INLINE bool
-S_aassign_common_vars_aliases_only(pTHX_ OP *o)
-{
- OP *curop;
- for (curop = cUNOPo->op_first; curop; curop = OpSIBLING(curop)) {
- if ((curop->op_type == OP_PADSV ||
- curop->op_type == OP_PADAV ||
- curop->op_type == OP_PADHV ||
- curop->op_type == OP_AELEMFAST_LEX ||
- curop->op_type == OP_PADANY ||
- ( PL_opargs[curop->op_type] & OA_TARGLEX
- && curop->op_private & OPpTARGET_MY ))
- && PAD_COMPNAME_GEN(curop->op_targ) == PERL_INT_MAX)
- return TRUE;
-
- if (curop->op_type == OP_PUSHRE && curop->op_targ
- && PAD_COMPNAME_GEN(curop->op_targ) == PERL_INT_MAX)
- return TRUE;
-
- if (curop->op_flags & OPf_KIDS) {
- if (S_aassign_common_vars_aliases_only(aTHX_ curop))
- return TRUE;
- }
- }
- return FALSE;
-}
/*
=for apidoc Am|OP *|newASSIGNOP|I32 flags|OP *left|I32 optype|OP *right
static const char no_list_state[] = "Initialization of state variables"
" in list context currently forbidden";
OP *curop;
- bool maybe_common_vars = TRUE;
if (left->op_type == OP_ASLICE || left->op_type == OP_HSLICE)
left->op_private &= ~ OPpSLICEWARNING;
if (OP_TYPE_IS_OR_WAS(left, OP_LIST))
{
OP* lop = ((LISTOP*)left)->op_first;
- maybe_common_vars = FALSE;
while (lop) {
- if (lop->op_type == OP_PADSV ||
- lop->op_type == OP_PADAV ||
- lop->op_type == OP_PADHV ||
- lop->op_type == OP_PADANY) {
- if (!(lop->op_private & OPpLVAL_INTRO))
- maybe_common_vars = TRUE;
-
- if (lop->op_private & OPpPAD_STATE) {
- if (left->op_private & OPpLVAL_INTRO) {
- /* Each variable in state($a, $b, $c) = ... */
- }
- else {
- /* Each state variable in
- (state $a, my $b, our $c, $d, undef) = ... */
- }
- yyerror(no_list_state);
- } else {
- /* Each my variable in
- (state $a, my $b, our $c, $d, undef) = ... */
- }
- } else if (lop->op_type == OP_UNDEF ||
- OP_TYPE_IS_OR_WAS(lop, OP_PUSHMARK)) {
- /* undef may be interesting in
- (state $a, undef, state $c) */
- } else {
- /* Other ops in the list. */
- maybe_common_vars = TRUE;
- }
+ if ((lop->op_type == OP_PADSV ||
+ lop->op_type == OP_PADAV ||
+ lop->op_type == OP_PADHV ||
+ lop->op_type == OP_PADANY)
+ && (lop->op_private & OPpPAD_STATE)
+ )
+ yyerror(no_list_state);
lop = OpSIBLING(lop);
}
}
- else if ((left->op_private & OPpLVAL_INTRO)
+ else if ( (left->op_private & OPpLVAL_INTRO)
+ && (left->op_private & OPpPAD_STATE)
&& ( left->op_type == OP_PADSV
|| left->op_type == OP_PADAV
|| left->op_type == OP_PADHV
- || left->op_type == OP_PADANY))
- {
- if (left->op_type == OP_PADSV) maybe_common_vars = FALSE;
- if (left->op_private & OPpPAD_STATE) {
+ || left->op_type == OP_PADANY)
+ ) {
/* All single variable list context state assignments, hence
state ($a) = ...
(state $a) = ...
(state %a) = ...
*/
yyerror(no_list_state);
- }
- }
-
- if (maybe_common_vars) {
- /* The peephole optimizer will do the full check and pos-
- sibly turn this off. */
- o->op_private |= OPpASSIGN_COMMON;
}
if (right && right->op_type == OP_SPLIT
assert (left);
assert (left->op_type == OP_SREFGEN);
- o->op_private = varop->op_private & (OPpLVAL_INTRO|OPpPAD_STATE);
+ o->op_private = 0;
+ /* we use OPpPAD_STATE in refassign to mean either of those things,
+ * and the code assumes the two flags occupy the same bit position
+ * in the various ops below */
+ assert(OPpPAD_STATE == OPpOUR_INTRO);
switch (varop->op_type) {
case OP_PADAV:
goto settarg;
case OP_PADHV:
o->op_private |= OPpLVREF_HV;
+ /* FALLTHROUGH */
case OP_PADSV:
settarg:
+ o->op_private |= (varop->op_private & (OPpLVAL_INTRO|OPpPAD_STATE));
o->op_targ = varop->op_targ;
varop->op_targ = 0;
PAD_COMPNAME_GEN_set(o->op_targ, PERL_INT_MAX);
break;
+
case OP_RV2AV:
o->op_private |= OPpLVREF_AV;
goto checkgv;
/* FALLTHROUGH */
case OP_RV2SV:
checkgv:
+ o->op_private |= (varop->op_private & (OPpLVAL_INTRO|OPpOUR_INTRO));
if (cUNOPx(varop)->op_first->op_type != OP_GV) goto bad;
detach_and_stack:
/* Point varop to its GV kid, detached. */
}
case OP_AELEM:
case OP_HELEM:
+ o->op_private |= (varop->op_private & OPpLVAL_INTRO);
o->op_private |= OPpLVREF_ELEM;
op_null(varop);
stacked = TRUE;
return o;
}
+
+
+/*
+ ---------------------------------------------------------
+
+ Common vars in list assignment
+
+ There now follows some enums and static functions for detecting
+ common variables in list assignments. Here is a little essay I wrote
+ for myself when trying to get my head around this. DAPM.
+
+ ----
+
+ First some random observations:
+
+ * If a lexical var is an alias of something else, e.g.
+ for my $x ($lex, $pkg, $a[0]) {...}
+ then the act of aliasing will increase the reference count of the SV
+
+ * If a package var is an alias of something else, it may still have a
+ reference count of 1, depending on how the alias was created, e.g.
+ in *a = *b, $a may have a refcount of 1 since the GP is shared
+ with a single GvSV pointer to the SV. So If it's an alias of another
+ package var, then RC may be 1; if it's an alias of another scalar, e.g.
+ a lexical var or an array element, then it will have RC > 1.
+
+ * There are many ways to create a package alias; ultimately, XS code
+ may quite legally do GvSV(gv) = SvREFCNT_inc(sv) for example, so
+ run-time tracing mechanisms are unlikely to be able to catch all cases.
+
+ * When the LHS is all my declarations, the same vars can't appear directly
+ on the RHS, but they can indirectly via closures, aliasing and lvalue
+ subs. But those techniques all involve an increase in the lexical
+ scalar's ref count.
+
+ * When the LHS is all lexical vars (but not necessarily my declarations),
+ it is possible for the same lexicals to appear directly on the RHS, and
+ without an increased ref count, since the stack isn't refcounted.
+ This case can be detected at compile time by scanning for common lex
+ vars with PL_generation.
+
+ * lvalue subs defeat common var detection, but they do at least
+ return vars with a temporary ref count increment. Also, you can't
+ tell at compile time whether a sub call is lvalue.
+
+
+ So...
+
+ A: There are a few circumstances where there definitely can't be any
+ commonality:
+
+ LHS empty: () = (...);
+ RHS empty: (....) = ();
+ RHS contains only constants or other 'can't possibly be shared'
+ elements (e.g. ops that return PADTMPs): (...) = (1,2, length)
+ i.e. they only contain ops not marked as dangerous, whose children
+ are also not dangerous;
+ LHS ditto;
+ LHS contains a single scalar element: e.g. ($x) = (....); because
+ after $x has been modified, it won't be used again on the RHS;
+ RHS contains a single element with no aggregate on LHS: e.g.
+ ($a,$b,$c) = ($x); again, once $a has been modified, its value
+ won't be used again.
+
+ B: If LHS are all 'my' lexical var declarations (or safe ops, which
+ we can ignore):
+
+ my ($a, $b, @c) = ...;
+
+ Due to closure and goto tricks, these vars may already have content.
+ For the same reason, an element on the RHS may be a lexical or package
+ alias of one of the vars on the left, or share common elements, for
+ example:
+
+ my ($x,$y) = f(); # $x and $y on both sides
+ sub f : lvalue { ($x,$y) = (1,2); $y, $x }
+
+ and
+
+ my $ra = f();
+ my @a = @$ra; # elements of @a on both sides
+ sub f { @a = 1..4; \@a }
+
+
+ First, just consider scalar vars on LHS:
+
+ RHS is safe only if (A), or in addition,
+ * contains only lexical *scalar* vars, where neither side's
+ lexicals have been flagged as aliases
+
+ If RHS is not safe, then it's always legal to check LHS vars for
+ RC==1, since the only RHS aliases will always be associated
+ with an RC bump.
+
+ Note that in particular, RHS is not safe if:
+
+ * it contains package scalar vars; e.g.:
+
+ f();
+ my ($x, $y) = (2, $x_alias);
+ sub f { $x = 1; *x_alias = \$x; }
+
+ * It contains other general elements, such as flattened or
+ * spliced or single array or hash elements, e.g.
+
+ f();
+ my ($x,$y) = @a; # or $a[0] or @a{@b} etc
+
+ sub f {
+ ($x, $y) = (1,2);
+ use feature 'refaliasing';
+ \($a[0], $a[1]) = \($y,$x);
+ }
+
+ It doesn't matter if the array/hash is lexical or package.
+
+ * it contains a function call that happens to be an lvalue
+ sub which returns one or more of the above, e.g.
+
+ f();
+ my ($x,$y) = f();
+
+ sub f : lvalue {
+ ($x, $y) = (1,2);
+ *x1 = \$x;
+ $y, $x1;
+ }
+
+ (so a sub call on the RHS should be treated the same
+ as having a package var on the RHS).
+
+ * any other "dangerous" thing, such an op or built-in that
+ returns one of the above, e.g. pp_preinc
+
+
+ If RHS is not safe, what we can do however is at compile time flag
+ that the LHS are all my declarations, and at run time check whether
+ all the LHS have RC == 1, and if so skip the full scan.
+
+ Now consider array and hash vars on LHS: e.g. my (...,@a) = ...;
+
+ Here the issue is whether there can be elements of @a on the RHS
+ which will get prematurely freed when @a is cleared prior to
+ assignment. This is only a problem if the aliasing mechanism
+ is one which doesn't increase the refcount - only if RC == 1
+ will the RHS element be prematurely freed.
+
+ Because the array/hash is being INTROed, it or its elements
+ can't directly appear on the RHS:
+
+ my (@a) = ($a[0], @a, etc) # NOT POSSIBLE
+
+ but can indirectly, e.g.:
+
+ my $r = f();
+ my (@a) = @$r;
+ sub f { @a = 1..3; \@a }
+
+ So if the RHS isn't safe as defined by (A), we must always
+ mortalise and bump the ref count of any remaining RHS elements
+ when assigning to a non-empty LHS aggregate.
+
+ Lexical scalars on the RHS aren't safe if they've been involved in
+ aliasing, e.g.
+
+ use feature 'refaliasing';
+
+ f();
+ \(my $lex) = \$pkg;
+ my @a = ($lex,3); # equivalent to ($a[0],3)
+
+ sub f {
+ @a = (1,2);
+ \$pkg = \$a[0];
+ }
+
+ Similarly with lexical arrays and hashes on the RHS:
+
+ f();
+ my @b;
+ my @a = (@b);
+
+ sub f {
+ @a = (1,2);
+ \$b[0] = \$a[1];
+ \$b[1] = \$a[0];
+ }
+
+
+
+ C: As (B), but in addition the LHS may contain non-intro lexicals, e.g.
+ my $a; ($a, my $b) = (....);
+
+ The difference between (B) and (C) is that it is now physically
+ possible for the LHS vars to appear on the RHS too, where they
+ are not reference counted; but in this case, the compile-time
+ PL_generation sweep will detect such common vars.
+
+ So the rules for (C) differ from (B) in that if common vars are
+ detected, the runtime "test RC==1" optimisation can no longer be used,
+ and a full mark and sweep is required
+
+ D: As (C), but in addition the LHS may contain package vars.
+
+ Since package vars can be aliased without a corresponding refcount
+ increase, all bets are off. It's only safe if (A). E.g.
+
+ my ($x, $y) = (1,2);
+
+ for $x_alias ($x) {
+ ($x_alias, $y) = (3, $x); # whoops
+ }
+
+ Ditto for LHS aggregate package vars.
+
+ E: Any other dangerous ops on LHS, e.g.
+ (f(), $a[0], @$r) = (...);
+
+ this is similar to (E) in that all bets are off. In addition, it's
+ impossible to determine at compile time whether the LHS
+ contains a scalar or an aggregate, e.g.
+
+ sub f : lvalue { @a }
+ (f()) = 1..3;
+
+* ---------------------------------------------------------
+*/
+
+
+/* A set of bit flags returned by S_aassign_scan(). Each flag indicates
+ * that at least one of the things flagged was seen.
+ */
+
+enum {
+ AAS_MY_SCALAR = 0x001, /* my $scalar */
+ AAS_MY_AGG = 0x002, /* aggregate: my @array or my %hash */
+ AAS_LEX_SCALAR = 0x004, /* $lexical */
+ AAS_LEX_AGG = 0x008, /* @lexical or %lexical aggregate */
+ AAS_LEX_SCALAR_COMM = 0x010, /* $lexical seen on both sides */
+ AAS_PKG_SCALAR = 0x020, /* $scalar (where $scalar is pkg var) */
+ AAS_PKG_AGG = 0x040, /* package @array or %hash aggregate */
+ AAS_DANGEROUS = 0x080, /* an op (other than the above)
+ that's flagged OA_DANGEROUS */
+ AAS_SAFE_SCALAR = 0x100, /* produces at least one scalar SV that's
+ not in any of the categories above */
+ AAS_DEFAV = 0x200, /* contains just a single '@_' on RHS */
+};
+
+
+
+/* helper function for S_aassign_scan().
+ * check a PAD-related op for commonality and/or set its generation number.
+ * Returns a boolean indicating whether its shared */
+
+static bool
+S_aassign_padcheck(pTHX_ OP* o, bool rhs)
+{
+ if (PAD_COMPNAME_GEN(o->op_targ) == PERL_INT_MAX)
+ /* lexical used in aliasing */
+ return TRUE;
+
+ if (rhs)
+ return cBOOL(PAD_COMPNAME_GEN(o->op_targ) == (STRLEN)PL_generation);
+ else
+ PAD_COMPNAME_GEN_set(o->op_targ, PL_generation);
+
+ return FALSE;
+}
+
+
+/*
+ Helper function for OPpASSIGN_COMMON* detection in rpeep().
+ It scans the left or right hand subtree of the aassign op, and returns a
+ set of flags indicating what sorts of things it found there.
+ 'rhs' indicates whether we're scanning the LHS or RHS. If the former, we
+ set PL_generation on lexical vars; if the latter, we see if
+ PL_generation matches.
+ 'top' indicates whether we're recursing or at the top level.
+ 'scalars_p' is a pointer to a counter of the number of scalar SVs seen.
+ This fn will increment it by the number seen. It's not intended to
+ be an accurate count (especially as many ops can push a variable
+ number of SVs onto the stack); rather it's used as to test whether there
+ can be at most 1 SV pushed; so it's only meanings are "0, 1, many".
+*/
+
+static int
+S_aassign_scan(pTHX_ OP* o, bool rhs, bool top, int *scalars_p)
+{
+ int flags = 0;
+ bool kid_top = FALSE;
+
+ /* first, look for a solitary @_ on the RHS */
+ if ( rhs
+ && top
+ && (o->op_flags & OPf_KIDS)
+ && OP_TYPE_IS_OR_WAS(o, OP_LIST)
+ ) {
+ OP *kid = cUNOPo->op_first;
+ if ( ( kid->op_type == OP_PUSHMARK
+ || kid->op_type == OP_PADRANGE) /* ex-pushmark */
+ && ((kid = OpSIBLING(kid)))
+ && !OpHAS_SIBLING(kid)
+ && kid->op_type == OP_RV2AV
+ && !(kid->op_flags & OPf_REF)
+ && !(kid->op_private & (OPpLVAL_INTRO|OPpMAYBE_LVSUB))
+ && ((kid->op_flags & OPf_WANT) == OPf_WANT_LIST)
+ && ((kid = cUNOPx(kid)->op_first))
+ && kid->op_type == OP_GV
+ && cGVOPx_gv(kid) == PL_defgv
+ )
+ flags |= AAS_DEFAV;
+ }
+
+ switch (o->op_type) {
+ case OP_GVSV:
+ (*scalars_p)++;
+ return AAS_PKG_SCALAR;
+
+ case OP_PADAV:
+ case OP_PADHV:
+ (*scalars_p) += 2;
+ if (top && (o->op_flags & OPf_REF))
+ return (o->op_private & OPpLVAL_INTRO)
+ ? AAS_MY_AGG : AAS_LEX_AGG;
+ return AAS_DANGEROUS;
+
+ case OP_PADSV:
+ {
+ int comm = S_aassign_padcheck(aTHX_ o, rhs)
+ ? AAS_LEX_SCALAR_COMM : 0;
+ (*scalars_p)++;
+ return (o->op_private & OPpLVAL_INTRO)
+ ? (AAS_MY_SCALAR|comm) : (AAS_LEX_SCALAR|comm);
+ }
+
+ case OP_RV2AV:
+ case OP_RV2HV:
+ (*scalars_p) += 2;
+ if (cUNOPx(o)->op_first->op_type != OP_GV)
+ return AAS_DANGEROUS; /* @{expr}, %{expr} */
+ /* @pkg, %pkg */
+ if (top && (o->op_flags & OPf_REF))
+ return AAS_PKG_AGG;
+ return AAS_DANGEROUS;
+
+ case OP_RV2SV:
+ (*scalars_p)++;
+ if (cUNOPx(o)->op_first->op_type != OP_GV) {
+ (*scalars_p) += 2;
+ return AAS_DANGEROUS; /* ${expr} */
+ }
+ return AAS_PKG_SCALAR; /* $pkg */
+
+ case OP_SPLIT:
+ if (cLISTOPo->op_first->op_type == OP_PUSHRE) {
+ /* "@foo = split... " optimises away the aassign and stores its
+ * destination array in the OP_PUSHRE that precedes it.
+ * A flattened array is always dangerous.
+ */
+ (*scalars_p) += 2;
+ return AAS_DANGEROUS;
+ }
+ break;
+
+ case OP_UNDEF:
+ case OP_PUSHMARK:
+ case OP_STUB:
+ /* these are all no-ops; they don't push a potentially common SV
+ * onto the stack, so they are neither AAS_DANGEROUS nor
+ * AAS_SAFE_SCALAR */
+ return 0;
+
+ case OP_PADRANGE: /* Ignore padrange; checking its siblings is enough */
+ break;
+
+ case OP_NULL:
+ case OP_LIST:
+ /* these do nothing but may have children; but their children
+ * should also be treated as top-level */
+ kid_top = top;
+ break;
+
+ default:
+ if (PL_opargs[o->op_type] & OA_DANGEROUS) {
+ (*scalars_p) += 2;
+ return AAS_DANGEROUS;
+ }
+
+ if ( (PL_opargs[o->op_type] & OA_TARGLEX)
+ && (o->op_private & OPpTARGET_MY))
+ {
+ (*scalars_p)++;
+ return S_aassign_padcheck(aTHX_ o, rhs)
+ ? AAS_LEX_SCALAR_COMM : AAS_LEX_SCALAR;
+ }
+
+ /* if its an unrecognised, non-dangerous op, assume that it
+ * it the cause of at least one safe scalar */
+ (*scalars_p)++;
+ flags = AAS_SAFE_SCALAR;
+ break;
+ }
+
+ if (o->op_flags & OPf_KIDS) {
+ OP *kid;
+ for (kid = cUNOPo->op_first; kid; kid = OpSIBLING(kid))
+ flags |= S_aassign_scan(aTHX_ kid, rhs, kid_top, scalars_p);
+ }
+ return flags;
+}
+
+
/* Check for in place reverse and sort assignments like "@a = reverse @a"
and modify the optree to make them work inplace */
}
break;
- case OP_AASSIGN:
- /* We do the common-vars check here, rather than in newASSIGNOP
- (as formerly), so that all lexical vars that get aliased are
- marked as such before we do the check. */
- /* There can’t be common vars if the lhs is a stub. */
- if (OpSIBLING(cLISTOPx(cBINOPo->op_last)->op_first)
- == cLISTOPx(cBINOPo->op_last)->op_last
- && cLISTOPx(cBINOPo->op_last)->op_last->op_type == OP_STUB)
- {
- o->op_private &=~ OPpASSIGN_COMMON;
- break;
- }
- if (o->op_private & OPpASSIGN_COMMON) {
- /* See the comment before S_aassign_common_vars concerning
- PL_generation sorcery. */
- PL_generation++;
- if (!aassign_common_vars(o))
- o->op_private &=~ OPpASSIGN_COMMON;
- }
- else if (S_aassign_common_vars_aliases_only(aTHX_ o))
- o->op_private |= OPpASSIGN_COMMON;
+ case OP_AASSIGN: {
+ int l, r, lr, lscalars, rscalars;
+
+ /* handle common vars detection, e.g. ($a,$b) = ($b,$a).
+ Note that we do this now rather than in newASSIGNOP(),
+ since only by now are aliased lexicals flagged as such
+
+ See the essay "Common vars in list assignment" above for
+ the full details of the rationale behind all the conditions
+ below.
+
+ PL_generation sorcery:
+ To detect whether there are common vars, the global var
+ PL_generation is incremented for each assign op we scan.
+ Then we run through all the lexical variables on the LHS,
+ of the assignment, setting a spare slot in each of them to
+ PL_generation. Then we scan the RHS, and if any lexicals
+ already have that value, we know we've got commonality.
+ Also, if the generation number is already set to
+ PERL_INT_MAX, then the variable is involved in aliasing, so
+ we also have potential commonality in that case.
+ */
+
+ PL_generation++;
+ /* scan LHS */
+ lscalars = 0;
+ l = S_aassign_scan(aTHX_ cLISTOPo->op_last, FALSE, 1, &lscalars);
+ /* scan RHS */
+ rscalars = 0;
+ r = S_aassign_scan(aTHX_ cLISTOPo->op_first, TRUE, 1, &rscalars);
+ lr = (l|r);
+
+
+ /* After looking for things which are *always* safe, this main
+ * if/else chain selects primarily based on the type of the
+ * LHS, gradually working its way down from the more dangerous
+ * to the more restrictive and thus safer cases */
+
+ if ( !l /* () = ....; */
+ || !r /* .... = (); */
+ || !(l & ~AAS_SAFE_SCALAR) /* (undef, pos()) = ...; */
+ || !(r & ~AAS_SAFE_SCALAR) /* ... = (1,2,length,undef); */
+ || (lscalars < 2) /* ($x) = ... */
+ ) {
+ NOOP; /* always safe */
+ }
+ else if (l & AAS_DANGEROUS) {
+ /* always dangerous */
+ o->op_private |= OPpASSIGN_COMMON_SCALAR;
+ o->op_private |= OPpASSIGN_COMMON_AGG;
+ }
+ else if (l & (AAS_PKG_SCALAR|AAS_PKG_AGG)) {
+ /* package vars are always dangerous - too many
+ * aliasing possibilities */
+ if (l & AAS_PKG_SCALAR)
+ o->op_private |= OPpASSIGN_COMMON_SCALAR;
+ if (l & AAS_PKG_AGG)
+ o->op_private |= OPpASSIGN_COMMON_AGG;
+ }
+ else if (l & ( AAS_MY_SCALAR|AAS_MY_AGG
+ |AAS_LEX_SCALAR|AAS_LEX_AGG))
+ {
+ /* LHS contains only lexicals and safe ops */
+
+ if (l & (AAS_MY_AGG|AAS_LEX_AGG))
+ o->op_private |= OPpASSIGN_COMMON_AGG;
+
+ if (l & (AAS_MY_SCALAR|AAS_LEX_SCALAR)) {
+ if (lr & AAS_LEX_SCALAR_COMM)
+ o->op_private |= OPpASSIGN_COMMON_SCALAR;
+ else if ( !(l & AAS_LEX_SCALAR)
+ && (r & AAS_DEFAV))
+ {
+ /* falsely mark
+ * my (...) = @_
+ * as scalar-safe for performance reasons.
+ * (it will still have been marked _AGG if necessary */
+ NOOP;
+ }
+ else if (r & (AAS_PKG_SCALAR|AAS_PKG_AGG|AAS_DANGEROUS))
+ o->op_private |= OPpASSIGN_COMMON_RC1;
+ }
+ }
+
+ /* ... = ($x)
+ * may have to handle aggregate on LHS, but we can't
+ * have common scalars*/
+ if (rscalars < 2)
+ o->op_private &=
+ ~(OPpASSIGN_COMMON_SCALAR|OPpASSIGN_COMMON_RC1);
+
break;
+ }
case OP_CUSTOM: {
Perl_cpeep_t cpeep =
https://perl5.git.perl.org / perl5.git / blobdiff