[llvm-commits] [parallel] CVS: llvm/runtime/zlib/contrib/asm586/README.586 match.S

Misha Brukman brukman at cs.uiuc.edu
Mon Mar 1 18:11:26 PST 2004


Changes in directory llvm/runtime/zlib/contrib/asm586:

README.586 added (r1.1.2.1)
match.S added (r1.1.2.1)

---
Log message:

Merge from trunk

---
Diffs of the changes:  (+397 -0)

Index: llvm/runtime/zlib/contrib/asm586/README.586
diff -c /dev/null llvm/runtime/zlib/contrib/asm586/README.586:1.1.2.1
*** /dev/null	Mon Mar  1 17:58:58 2004
--- llvm/runtime/zlib/contrib/asm586/README.586	Mon Mar  1 17:58:48 2004
***************
*** 0 ****
--- 1,43 ----
+ This is a patched version of zlib modified to use
+ Pentium-optimized assembly code in the deflation algorithm. The files
+ changed/added by this patch are:
+ 
+ README.586
+ match.S
+ 
+ The effectiveness of these modifications is a bit marginal, as the the
+ program's bottleneck seems to be mostly L1-cache contention, for which
+ there is no real way to work around without rewriting the basic
+ algorithm. The speedup on average is around 5-10% (which is generally
+ less than the amount of variance between subsequent executions).
+ However, when used at level 9 compression, the cache contention can
+ drop enough for the assembly version to achieve 10-20% speedup (and
+ sometimes more, depending on the amount of overall redundancy in the
+ files). Even here, though, cache contention can still be the limiting
+ factor, depending on the nature of the program using the zlib library.
+ This may also mean that better improvements will be seen on a Pentium
+ with MMX, which suffers much less from L1-cache contention, but I have
+ not yet verified this.
+ 
+ Note that this code has been tailored for the Pentium in particular,
+ and will not perform well on the Pentium Pro (due to the use of a
+ partial register in the inner loop).
+ 
+ If you are using an assembler other than GNU as, you will have to
+ translate match.S to use your assembler's syntax. (Have fun.)
+ 
+ Brian Raiter
+ breadbox at muppetlabs.com
+ April, 1998
+ 
+ 
+ Added for zlib 1.1.3:
+ 
+ The patches come from
+ http://www.muppetlabs.com/~breadbox/software/assembly.html
+ 
+ To compile zlib with this asm file, copy match.S to the zlib directory
+ then do:
+ 
+ CFLAGS="-O3 -DASMV" ./configure
+ make OBJA=match.o


Index: llvm/runtime/zlib/contrib/asm586/match.S
diff -c /dev/null llvm/runtime/zlib/contrib/asm586/match.S:1.1.2.1
*** /dev/null	Mon Mar  1 17:58:58 2004
--- llvm/runtime/zlib/contrib/asm586/match.S	Mon Mar  1 17:58:48 2004
***************
*** 0 ****
--- 1,354 ----
+ /* match.s -- Pentium-optimized version of longest_match()
+  * Written for zlib 1.1.2
+  * Copyright (C) 1998 Brian Raiter <breadbox at muppetlabs.com>
+  *
+  * This is free software; you can redistribute it and/or modify it
+  * under the terms of the GNU General Public License.
+  */
+ 
+ #ifndef NO_UNDERLINE
+ #define	match_init	_match_init
+ #define	longest_match	_longest_match
+ #endif
+ 
+ #define	MAX_MATCH	(258)
+ #define	MIN_MATCH	(3)
+ #define	MIN_LOOKAHEAD	(MAX_MATCH + MIN_MATCH + 1)
+ #define	MAX_MATCH_8	((MAX_MATCH + 7) & ~7)
+ 
+ /* stack frame offsets */
+ 
+ #define	wmask			0	/* local copy of s->wmask	*/
+ #define	window			4	/* local copy of s->window	*/
+ #define	windowbestlen		8	/* s->window + bestlen		*/
+ #define	chainlenscanend		12	/* high word: current chain len	*/
+ 					/* low word: last bytes sought	*/
+ #define	scanstart		16	/* first two bytes of string	*/
+ #define	scanalign		20	/* dword-misalignment of string	*/
+ #define	nicematch		24	/* a good enough match size	*/
+ #define	bestlen			28	/* size of best match so far	*/
+ #define	scan			32	/* ptr to string wanting match	*/
+ 
+ #define	LocalVarsSize		(36)
+ /*	saved ebx		36 */
+ /*	saved edi		40 */
+ /*	saved esi		44 */
+ /*	saved ebp		48 */
+ /*	return address		52 */
+ #define	deflatestate		56	/* the function arguments	*/
+ #define	curmatch		60
+ 
+ /* Offsets for fields in the deflate_state structure. These numbers
+  * are calculated from the definition of deflate_state, with the
+  * assumption that the compiler will dword-align the fields. (Thus,
+  * changing the definition of deflate_state could easily cause this
+  * program to crash horribly, without so much as a warning at
+  * compile time. Sigh.)
+  */
+ #define	dsWSize			36
+ #define	dsWMask			44
+ #define	dsWindow		48
+ #define	dsPrev			56
+ #define	dsMatchLen		88
+ #define	dsPrevMatch		92
+ #define	dsStrStart		100
+ #define	dsMatchStart		104
+ #define	dsLookahead		108
+ #define	dsPrevLen		112
+ #define	dsMaxChainLen		116
+ #define	dsGoodMatch		132
+ #define	dsNiceMatch		136
+ 
+ 
+ .file "match.S"
+ 
+ .globl	match_init, longest_match
+ 
+ .text
+ 
+ /* uInt longest_match(deflate_state *deflatestate, IPos curmatch) */
+ 
+ longest_match:
+ 
+ /* Save registers that the compiler may be using, and adjust %esp to	*/
+ /* make room for our stack frame.					*/
+ 
+ 		pushl	%ebp
+ 		pushl	%edi
+ 		pushl	%esi
+ 		pushl	%ebx
+ 		subl	$LocalVarsSize, %esp
+ 
+ /* Retrieve the function arguments. %ecx will hold cur_match		*/
+ /* throughout the entire function. %edx will hold the pointer to the	*/
+ /* deflate_state structure during the function's setup (before		*/
+ /* entering the main loop).						*/
+ 
+ 		movl	deflatestate(%esp), %edx
+ 		movl	curmatch(%esp), %ecx
+ 
+ /* if ((uInt)nice_match > s->lookahead) nice_match = s->lookahead;	*/
+ 
+ 		movl	dsNiceMatch(%edx), %eax
+ 		movl	dsLookahead(%edx), %ebx
+ 		cmpl	%eax, %ebx
+ 		jl	LookaheadLess
+ 		movl	%eax, %ebx
+ LookaheadLess:	movl	%ebx, nicematch(%esp)
+ 
+ /* register Bytef *scan = s->window + s->strstart;			*/
+ 
+ 		movl	dsWindow(%edx), %esi
+ 		movl	%esi, window(%esp)
+ 		movl	dsStrStart(%edx), %ebp
+ 		lea	(%esi,%ebp), %edi
+ 		movl	%edi, scan(%esp)
+ 
+ /* Determine how many bytes the scan ptr is off from being		*/
+ /* dword-aligned.							*/
+ 
+ 		movl	%edi, %eax
+ 		negl	%eax
+ 		andl	$3, %eax
+ 		movl	%eax, scanalign(%esp)
+ 
+ /* IPos limit = s->strstart > (IPos)MAX_DIST(s) ?			*/
+ /*     s->strstart - (IPos)MAX_DIST(s) : NIL;				*/
+ 
+ 		movl	dsWSize(%edx), %eax
+ 		subl	$MIN_LOOKAHEAD, %eax
+ 		subl	%eax, %ebp
+ 		jg	LimitPositive
+ 		xorl	%ebp, %ebp
+ LimitPositive:
+ 
+ /* unsigned chain_length = s->max_chain_length;				*/
+ /* if (s->prev_length >= s->good_match) {				*/
+ /*     chain_length >>= 2;						*/
+ /* }									*/
+ 
+ 		movl	dsPrevLen(%edx), %eax
+ 		movl	dsGoodMatch(%edx), %ebx
+ 		cmpl	%ebx, %eax
+ 		movl	dsMaxChainLen(%edx), %ebx
+ 		jl	LastMatchGood
+ 		shrl	$2, %ebx
+ LastMatchGood:
+ 
+ /* chainlen is decremented once beforehand so that the function can	*/
+ /* use the sign flag instead of the zero flag for the exit test.	*/
+ /* It is then shifted into the high word, to make room for the scanend	*/
+ /* scanend value, which it will always accompany.			*/
+ 
+ 		decl	%ebx
+ 		shll	$16, %ebx
+ 
+ /* int best_len = s->prev_length;					*/
+ 
+ 		movl	dsPrevLen(%edx), %eax
+ 		movl	%eax, bestlen(%esp)
+ 
+ /* Store the sum of s->window + best_len in %esi locally, and in %esi.	*/
+ 
+ 		addl	%eax, %esi
+ 		movl	%esi, windowbestlen(%esp)
+ 
+ /* register ush scan_start = *(ushf*)scan;				*/
+ /* register ush scan_end   = *(ushf*)(scan+best_len-1);			*/
+ 
+ 		movw	(%edi), %bx
+ 		movw	%bx, scanstart(%esp)
+ 		movw	-1(%edi,%eax), %bx
+ 		movl	%ebx, chainlenscanend(%esp)
+ 
+ /* Posf *prev = s->prev;						*/
+ /* uInt wmask = s->w_mask;						*/
+ 
+ 		movl	dsPrev(%edx), %edi
+ 		movl	dsWMask(%edx), %edx
+ 		mov	%edx, wmask(%esp)
+ 
+ /* Jump into the main loop.						*/
+ 
+ 		jmp	LoopEntry
+ 
+ .balign 16
+ 
+ /* do {
+  *     match = s->window + cur_match;
+  *     if (*(ushf*)(match+best_len-1) != scan_end ||
+  *         *(ushf*)match != scan_start) continue;
+  *     [...]
+  * } while ((cur_match = prev[cur_match & wmask]) > limit
+  *          && --chain_length != 0);
+  *
+  * Here is the inner loop of the function. The function will spend the
+  * majority of its time in this loop, and majority of that time will
+  * be spent in the first ten instructions.
+  *
+  * Within this loop:
+  * %ebx = chainlenscanend - i.e., ((chainlen << 16) | scanend)
+  * %ecx = curmatch
+  * %edx = curmatch & wmask
+  * %esi = windowbestlen - i.e., (window + bestlen)
+  * %edi = prev
+  * %ebp = limit
+  *
+  * Two optimization notes on the choice of instructions:
+  *
+  * The first instruction uses a 16-bit address, which costs an extra,
+  * unpairable cycle. This is cheaper than doing a 32-bit access and
+  * zeroing the high word, due to the 3-cycle misalignment penalty which
+  * would occur half the time. This also turns out to be cheaper than
+  * doing two separate 8-bit accesses, as the memory is so rarely in the
+  * L1 cache.
+  *
+  * The window buffer, however, apparently spends a lot of time in the
+  * cache, and so it is faster to retrieve the word at the end of the
+  * match string with two 8-bit loads. The instructions that test the
+  * word at the beginning of the match string, however, are executed
+  * much less frequently, and there it was cheaper to use 16-bit
+  * instructions, which avoided the necessity of saving off and
+  * subsequently reloading one of the other registers.
+  */
+ LookupLoop:
+ 							/* 1 U & V  */
+ 		movw	(%edi,%edx,2), %cx		/* 2 U pipe */
+ 		movl	wmask(%esp), %edx		/* 2 V pipe */
+ 		cmpl	%ebp, %ecx			/* 3 U pipe */
+ 		jbe	LeaveNow			/* 3 V pipe */
+ 		subl	$0x00010000, %ebx		/* 4 U pipe */
+ 		js	LeaveNow			/* 4 V pipe */
+ LoopEntry:	movb	-1(%esi,%ecx), %al		/* 5 U pipe */
+ 		andl	%ecx, %edx			/* 5 V pipe */
+ 		cmpb	%bl, %al			/* 6 U pipe */
+ 		jnz	LookupLoop			/* 6 V pipe */
+ 		movb	(%esi,%ecx), %ah
+ 		cmpb	%bh, %ah
+ 		jnz	LookupLoop
+ 		movl	window(%esp), %eax
+ 		movw	(%eax,%ecx), %ax
+ 		cmpw	scanstart(%esp), %ax
+ 		jnz	LookupLoop
+ 
+ /* Store the current value of chainlen.					*/
+ 
+ 		movl	%ebx, chainlenscanend(%esp)
+ 
+ /* Point %edi to the string under scrutiny, and %esi to the string we	*/
+ /* are hoping to match it up with. In actuality, %esi and %edi are	*/
+ /* both pointed (MAX_MATCH_8 - scanalign) bytes ahead, and %edx is	*/
+ /* initialized to -(MAX_MATCH_8 - scanalign).				*/
+ 
+ 		movl	window(%esp), %esi
+ 		movl	scan(%esp), %edi
+ 		addl	%ecx, %esi
+ 		movl	scanalign(%esp), %eax
+ 		movl	$(-MAX_MATCH_8), %edx
+ 		lea	MAX_MATCH_8(%edi,%eax), %edi
+ 		lea	MAX_MATCH_8(%esi,%eax), %esi
+ 
+ /* Test the strings for equality, 8 bytes at a time. At the end,
+  * adjust %edx so that it is offset to the exact byte that mismatched.
+  *
+  * We already know at this point that the first three bytes of the
+  * strings match each other, and they can be safely passed over before
+  * starting the compare loop. So what this code does is skip over 0-3
+  * bytes, as much as necessary in order to dword-align the %edi
+  * pointer. (%esi will still be misaligned three times out of four.)
+  *
+  * It should be confessed that this loop usually does not represent
+  * much of the total running time. Replacing it with a more
+  * straightforward "rep cmpsb" would not drastically degrade
+  * performance.
+  */
+ LoopCmps:
+ 		movl	(%esi,%edx), %eax
+ 		movl	(%edi,%edx), %ebx
+ 		xorl	%ebx, %eax
+ 		jnz	LeaveLoopCmps
+ 		movl	4(%esi,%edx), %eax
+ 		movl	4(%edi,%edx), %ebx
+ 		xorl	%ebx, %eax
+ 		jnz	LeaveLoopCmps4
+ 		addl	$8, %edx
+ 		jnz	LoopCmps
+ 		jmp	LenMaximum
+ LeaveLoopCmps4:	addl	$4, %edx
+ LeaveLoopCmps:	testl	$0x0000FFFF, %eax
+ 		jnz	LenLower
+ 		addl	$2, %edx
+ 		shrl	$16, %eax
+ LenLower:	subb	$1, %al
+ 		adcl	$0, %edx
+ 
+ /* Calculate the length of the match. If it is longer than MAX_MATCH,	*/
+ /* then automatically accept it as the best possible match and leave.	*/
+ 
+ 		lea	(%edi,%edx), %eax
+ 		movl	scan(%esp), %edi
+ 		subl	%edi, %eax
+ 		cmpl	$MAX_MATCH, %eax
+ 		jge	LenMaximum
+ 
+ /* If the length of the match is not longer than the best match we	*/
+ /* have so far, then forget it and return to the lookup loop.		*/
+ 
+ 		movl	deflatestate(%esp), %edx
+ 		movl	bestlen(%esp), %ebx
+ 		cmpl	%ebx, %eax
+ 		jg	LongerMatch
+ 		movl	chainlenscanend(%esp), %ebx
+ 		movl	windowbestlen(%esp), %esi
+ 		movl	dsPrev(%edx), %edi
+ 		movl	wmask(%esp), %edx
+ 		andl	%ecx, %edx
+ 		jmp	LookupLoop
+ 
+ /*         s->match_start = cur_match;					*/
+ /*         best_len = len;						*/
+ /*         if (len >= nice_match) break;				*/
+ /*         scan_end = *(ushf*)(scan+best_len-1);			*/
+ 
+ LongerMatch:	movl	nicematch(%esp), %ebx
+ 		movl	%eax, bestlen(%esp)
+ 		movl	%ecx, dsMatchStart(%edx)
+ 		cmpl	%ebx, %eax
+ 		jge	LeaveNow
+ 		movl	window(%esp), %esi
+ 		addl	%eax, %esi
+ 		movl	%esi, windowbestlen(%esp)
+ 		movl	chainlenscanend(%esp), %ebx
+ 		movw	-1(%edi,%eax), %bx
+ 		movl	dsPrev(%edx), %edi
+ 		movl	%ebx, chainlenscanend(%esp)
+ 		movl	wmask(%esp), %edx
+ 		andl	%ecx, %edx
+ 		jmp	LookupLoop
+ 
+ /* Accept the current string, with the maximum possible length.		*/
+ 
+ LenMaximum:	movl	deflatestate(%esp), %edx
+ 		movl	$MAX_MATCH, bestlen(%esp)
+ 		movl	%ecx, dsMatchStart(%edx)
+ 
+ /* if ((uInt)best_len <= s->lookahead) return (uInt)best_len;		*/
+ /* return s->lookahead;							*/
+ 
+ LeaveNow:
+ 		movl	deflatestate(%esp), %edx
+ 		movl	bestlen(%esp), %ebx
+ 		movl	dsLookahead(%edx), %eax
+ 		cmpl	%eax, %ebx
+ 		jg	LookaheadRet
+ 		movl	%ebx, %eax
+ LookaheadRet:
+ 
+ /* Restore the stack and return from whence we came.			*/
+ 
+ 		addl	$LocalVarsSize, %esp
+ 		popl	%ebx
+ 		popl	%esi
+ 		popl	%edi
+ 		popl	%ebp
+ match_init:	ret





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