More variable reordering saves another 40 bytes from the interpreter

structure. (on LP64). Zero cost space saving! Woohoo!

p4raw-id: //depot/perl@31034

3 files changed, 60 insertions, 74 deletions

diff --git a/intrpvar.h b/intrpvar.h
index 0da8516669..57afeb23dd 100644
--- a/intrpvar.h
+++ b/intrpvar.h
@@ -16,7 +16,19 @@
  *
  * When building without MULTIPLICITY, these variables will be truly global. */
 
+
+/* For historical reasons this file follows thrdvar.h into the interpeter
+   struct, and that file currently ends with 7 bytes of variables, so putting
+   one last byte here is good for alignment.  */
+
+/* This value may be set when embedding for full cleanup  */
+/* 0=none, 1=full, 2=full with checks */
+PERLVARI(Iperl_destruct_level,	U8,	0)
+
+PERLVAR(Iperldb,	U32)
+
 /* pseudo environmental stuff */
+PERLVAR(Iorigargc,	int)
 PERLVAR(Iorigargv,	char **)
 PERLVAR(Ienvgv,		GV *)
 PERLVAR(Iincgv,		GV *)
@@ -61,11 +73,6 @@ PERLVAR(Isrand_called,	bool)
 PERLVAR(Itainting,	bool)		/* doing taint checks */
 PERLVAR(Iinplace,	char *)
 PERLVAR(Ie_script,	SV *)
-PERLVAR(Iperldb,	U32)
-
-/* This value may be set when embedding for full cleanup  */
-/* 0=none, 1=full, 2=full with checks */
-PERLVARI(Iperl_destruct_level,	U8,	0)
 
 /* magical thingies */
 PERLVAR(Ibasetime,	Time_t)		/* $^T */
@@ -81,8 +88,10 @@ PERLVAR(Istatusvalue_vms,U32)
 PERLVAR(Istatusvalue_posix,I32)
 #endif
 
-/* Moved here to give an even number of adjacent I32s/U32s/ints */
-PERLVAR(Iorigargc,	int)
+#ifdef CSH
+PERLVARI(Icshlen,	I32,	0)
+PERLVARI(Icshname,	const char *,	CSH)
+#endif
 
 /* shortcuts to various I/O objects */
 PERLVAR(Istdingv,	GV *)
@@ -179,17 +188,18 @@ PERLVAR(Ioldname,	char *)		/* what to preserve mode on */
 PERLVAR(IArgv,		char **)	/* stuff to free from do_aexec, vfork safe */
 PERLVAR(ICmd,		char *)		/* stuff to free from do_aexec, vfork safe */
 PERLVAR(Ipreambleav,	AV *)
-PERLVARI(Ilaststatval,	int,	-1)
-PERLVARI(Ilaststype,	U16,	OP_STAT)
 PERLVAR(Imess_sv,	SV *)
-
-/* XXX shouldn't these be per-thread? --GSAR */
 PERLVAR(Iors_sv,	SV *)		/* output record separator $\ */
+     /* Space for one more U16 here without increasing the structure size */
+PERLVAR(Ilast_lop_op,	OPCODE)		/* last list operator */
+PERLVAR(Iin_my,		U16)		/* we're compiling a "my" (or "our") declaration */
+PERLVARI(Ilaststype,	U16,	OP_STAT)
+PERLVARI(Ilaststatval,	int,	-1)
 
 /* interpreter atexit processing */
+PERLVARI(Iexitlistlen,	I32, 0)		/* length of same */
 PERLVARI(Iexitlist,	PerlExitListEntry *, NULL)
 					/* list of exit functions */
-PERLVARI(Iexitlistlen,	I32, 0)		/* length of same */
 
 /*
 =for apidoc Amn|HV*|PL_modglobal
@@ -280,13 +290,6 @@ PERLVAR(Isv_undef,	SV)
 PERLVAR(Isv_no,		SV)
 PERLVAR(Isv_yes,	SV)
 
-#ifdef CSH
-PERLVARI(Icshname,	const char *,	CSH)
-PERLVARI(Icshlen,	I32,	0)
-#endif
-
-PERLVAR(Ilex_state,	U8)		/* next token is determined */
-
 /* What we know when we're in LEX_KNOWNEXT state. */
 #ifdef PERL_MAD
 PERLVARA(Inexttoke,5,	NEXTTOKE)	/* value of next token, if any */
@@ -302,28 +305,27 @@ PERLVAR(Ibufptr,	char *)
 PERLVAR(Ioldbufptr,	char *)
 PERLVAR(Ioldoldbufptr,	char *)
 PERLVAR(Ibufend,	char *)
-PERLVARI(Iexpect, U8,	XSTATE)		/* how to interpret ambiguous tokens */
 
+PERLVARI(Iexpect, U8,	XSTATE)		/* how to interpret ambiguous tokens */
+PERLVAR(Ilex_state,	U8)		/* next token is determined */
+PERLVAR(Ierror_count,	U8)		/* how many errors so far, max 10 */
+PERLVARI(Icv_has_eval, bool, FALSE) /* PL_compcv includes an entereval or similar */
 PERLVAR(Imulti_end,	I32)		/* last line of multi-line string */
 
-PERLVAR(Ierror_count,	U8)		/* how many errors so far, max 10 */
-PERLVAR(Isubline,	I32)		/* line this subroutine began on */
 PERLVAR(Isubname,	SV *)		/* name of current subroutine */
 
+PERLVAR(Isubline,	I32)		/* line this subroutine began on */
 PERLVAR(Imin_intro_pending,	I32)	/* start of vars to introduce */
+
 PERLVAR(Imax_intro_pending,	I32)	/* end of vars to introduce */
 PERLVAR(Ipadix,		I32)		/* max used index in current "register" pad */
+
 PERLVAR(Ipadix_floor,	I32)		/* how low may inner block reset padix */
 PERLVAR(Ipad_reset_pending,	I32)	/* reset pad on next attempted alloc */
 
 PERLVAR(Ilast_uni,	char *)		/* position of last named-unary op */
 PERLVAR(Ilast_lop,	char *)		/* position of last list operator */
-PERLVAR(Ilast_lop_op,	OPCODE)		/* last list operator */
-PERLVAR(Iin_my,		U16)		/* we're compiling a "my" (or "our") declaration */
 PERLVAR(Iin_my_stash,	HV *)		/* declared class of this "my" declaration */
-#ifdef FCRYPT
-PERLVARI(Icryptseen,	bool,	FALSE)	/* has fast crypt() been initialized? */
-#endif
 
 PERLVAR(Ihints,		U32)		/* pragma-tic compile-time flags */
 
@@ -378,9 +380,15 @@ PERLVAR(Iutf8_tofold,	SV *)
 PERLVAR(Ilast_swash_hv,	HV *)
 PERLVAR(Ilast_swash_tmps,	U8 *)
 PERLVAR(Ilast_swash_slen,	STRLEN)
-PERLVARI(Iglob_index,	int,	0)
-PERLVAR(Ilast_swash_klen,	U8)	/* Only needs to store 0-10  */
 PERLVARA(Ilast_swash_key,10,	U8)
+PERLVAR(Ilast_swash_klen,	U8)	/* Only needs to store 0-10  */
+
+#ifdef FCRYPT
+PERLVARI(Icryptseen,	bool,	FALSE)	/* has fast crypt() been initialized? */
+#endif
+
+PERLVARI(Iglob_index,	int,	0)
+
 
 PERLVAR(Iparser,	yy_parser *)	/* current parser state */
 
@@ -410,6 +418,12 @@ PERLVAR(Ibody_arenas, void*) /* pointer to list of body-arenas */
 PERLVAR(Ipsig_pend, int *)		/* per-signal "count" of pending */
 PERLVARI(Isig_pending, int,0)           /* Number if highest signal pending */
 
+
+PERLVAR(Itaint_warn,	bool)      /* taint warns instead of dying */
+PERLVAR(Iutf8locale,	bool)		/* utf8 locale detected */
+PERLVARI(Ihash_seed_set, bool, FALSE)		/* Hash initialized? */
+PERLVARI(Irehash_seed_set, bool, FALSE)	/* 582 hash initialized? */
+
 #ifdef USE_LOCALE_NUMERIC
 
 PERLVAR(Inumeric_radix_sv,	SV *)	/* The radix separator if not '.' */
@@ -446,13 +460,6 @@ PERLVARI(Iencoding,	SV*, NULL)		/* character encoding */
 
 PERLVAR(Idebug_pad,	struct perl_debug_pad)	/* always needed because of the re extension */
 
-PERLVAR(Itaint_warn,	bool)      /* taint warns instead of dying */
-PERLVAR(Iutf8locale,	bool)		/* utf8 locale detected */
-PERLVARI(Ihash_seed_set, bool, FALSE)		/* Hash initialized? */
-PERLVARI(Irehash_seed_set, bool, FALSE)	/* 582 hash initialized? */
-
-PERLVARI(Icv_has_eval, bool, FALSE) /* PL_compcv includes an entereval or similar */
-
 #ifdef PL_OP_SLAB_ALLOC
 PERLVAR(IOpPtr,I32 **)
 PERLVARI(IOpSpace,I32,0)
@@ -530,8 +537,12 @@ PERLVARI(Islabs, I32**, NULL)	/* Array of slabs that have been allocated */
 PERLVARI(Islab_count, U32, 0)	/* Size of the array */
 #endif
 
-/* New variables must be added to the very end, before this comment,
- * for binary compatibility (the offsets of the old members must not change).
+/* If you are adding a U16, see the comment above on where there are 2 bytes
+   of gap which currently will be structure padding.  */
+
+/* Within a stable branch, new variables must be added to the very end, before
+ * this comment, for binary compatibility (the offsets of the old members must
+ *  not change).
  * (Don't forget to add your variable also to perl_clone()!)
  * XSUB.h provides wrapper functions via perlapi.h that make this
  * irrelevant, but not all code may be expected to #include XSUB.h.
diff --git a/pod/perltodo.pod b/pod/perltodo.pod
index 1c8496c051..46619239e2 100644
--- a/pod/perltodo.pod
+++ b/pod/perltodo.pod
@@ -332,37 +332,6 @@ such that it's trivial for the Pumpking to flag "this is an official release"
 when making a tarball, yet leave the default source saying "I'm not the
 official release".
 
-=head2 Ordering of "global" variables.
-
-F<thrdvar.h> and F<intrpvarh> define the "global" variables that need to be
-per-thread under ithreads, where the variables are actually elements in a
-structure. As C dictates, the variables must be laid out in order of
-declaration. There is a comment
-C</* Important ones in the first cache line (if alignment is done right) */>
-which implies that at some point in the past the ordering was carefully chosen
-(at least in part). However, it's clear that the ordering is less than perfect,
-as currently there are things such as 7 C<bool>s in a row, then something
-typically requiring 4 byte alignment, and then an odd C<bool> later on.
-(C<bool>s are typically defined as C<char>s). So it would be good for someone
-to review the ordering of the variables, to see how much alignment padding can
-be removed.
-
-It's also worth checking that all variables are actually used. Perl 5.8.0
-shipped with C<PL_nrs> still defined in F<thrdvar.h>, despite it being unused
-since a change over a year earlier. Had this been spotted before release, it
-could have been removed, but now it has to remain in the 5.8.x releases to
-keep the structure the same size, to retain binary compatibility.
-
-It's probably worth checking if all need to be the types they are. For example
-
-    PERLVAR(Ierror_count, I32)	/* how many errors so far, max 10 */
-
-might work as well if stored in a signed (or unsigned) 8 bit value, if the
-comment is accurate. C<PL_multi_open> and C<PL_multi_close> can probably
-become C<char>s. Finding variables to downsize coupled with rearrangement
-could shrink the interpreter structure; a size saving which is multiplied by
-the number of threads running.
-
 =head2 Profile Perl - am I hot or not?
 
 The Perl source code is stable enough that it makes sense to profile it,
diff --git a/thrdvar.h b/thrdvar.h
index bf253512d2..4f49ef8442 100644
--- a/thrdvar.h
+++ b/thrdvar.h
@@ -1,6 +1,6 @@
 /*    thdrvar.h
  *
- *    Copyright (C) 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006
+ *    Copyright (C) 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007
  *    by Larry Wall and others
  *
  *    You may distribute under the terms of either the GNU General Public
@@ -119,9 +119,6 @@ PERLVAR(Tcurstash,	HV *)		/* symbol table for current package */
 
 PERLVAR(Trestartop,	OP *)		/* propagating an error from croak? */
 PERLVARI(Tcurcop,	COP * VOL,	&PL_compiling)
-PERLVAR(Tlocalizing,	U8)		/* are we processing a local() list? */
-PERLVAR(Tcolorset,	bool)		/* from regcomp.c */
-
 PERLVAR(Tcurstack,	AV *)		/* THE STACK */
 PERLVAR(Tcurstackinfo,	PERL_SI *)	/* current stack + context */
 PERLVAR(Tmainstack,	AV *)		/* the stack when nothing funny is happening */
@@ -137,7 +134,6 @@ PERLVAR(Thv_fetch_ent_mh, HE*)		/* owned by hv_fetch_ent() */
 
 
 PERLVAR(Tlastgotoprobe,	OP*)		/* from pp_ctl.c */
-PERLVARI(Tdumpindent,	U16, 4)		/* # of blanks per dump indentation level */
 
 /* sort stuff */
 PERLVAR(Tsortcop,	OP *)		/* user defined sort routine */
@@ -176,7 +172,17 @@ PERLVAR(Twatchok,	char *)
 PERLVARI(Tregmatch_slab,	regmatch_slab *, NULL)
 PERLVAR(Tregmatch_state,	regmatch_state *)
 
+PERLVARI(Tdumpindent,	U16, 4)		/* # of blanks per dump indentation level */
+
+/* Put anything new that is pointer aligned here. */
+
 PERLVAR(Tdelaymagic,	U16)		/* ($<,$>) = ... */
+PERLVAR(Tlocalizing,	U8)		/* are we processing a local() list? */
+PERLVAR(Tcolorset,	bool)		/* from regcomp.c */
 PERLVARI(Tdirty,	bool, FALSE)	/* in the middle of tearing things down? */
 PERLVAR(Tin_eval,	VOL U8)	/* trap "fatal" errors? */
 PERLVAR(Ttainted,	bool)		/* using variables controlled by $< */
+
+/* For historical reasons this file is followed by intrpvar.h in the interpeter
+   struct. As this file currently ends with 7 bytes of variables, intrpvar.h
+   starts with one single U8, to avoid structure padding space wastage.  */