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Subject[PATCH] lib/lz4: Pull out constant tables
Date
There's no reason to allocate the dec{32,64}table on the stack; it
just wastes a bunch of instructions setting them up and, of course,
also consumes quite a bit of stack. Using size_t for such small
integers is a little excessive.

$ scripts/bloat-o-meter /tmp/built-in.o lib/built-in.o
add/remove: 2/2 grow/shrink: 2/0 up/down: 1304/-1548 (-244)
function old new delta
lz4_decompress_unknownoutputsize 55 718 +663
lz4_decompress 55 632 +577
dec64table - 32 +32
dec32table - 32 +32
lz4_uncompress 747 - -747
lz4_uncompress_unknownoutputsize 801 - -801

The now inlined lz4_uncompress functions used to have a stack
footprint of 176 bytes (according to -fstack-usage); their inlinees
have increased their stack use from 32 bytes to 48 and 80 bytes,
respectively.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
lib/lz4/lz4_decompress.c | 18 +++++++-----------
1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/lib/lz4/lz4_decompress.c b/lib/lz4/lz4_decompress.c
index 7a85967060a5..f2b95d4fbed5 100644
--- a/lib/lz4/lz4_decompress.c
+++ b/lib/lz4/lz4_decompress.c
@@ -47,6 +47,11 @@

#include "lz4defs.h"

+static const int dec32table[] = {0, 3, 2, 3, 0, 0, 0, 0};
+#if LZ4_ARCH64
+static const int dec64table[] = {0, 0, 0, -1, 0, 1, 2, 3};
+#endif
+
static int lz4_uncompress(const char *source, char *dest, int osize)
{
const BYTE *ip = (const BYTE *) source;
@@ -56,10 +61,6 @@ static int lz4_uncompress(const char *source, char *dest, int osize)
BYTE *cpy;
unsigned token;
size_t length;
- size_t dec32table[] = {0, 3, 2, 3, 0, 0, 0, 0};
-#if LZ4_ARCH64
- size_t dec64table[] = {0, 0, 0, -1, 0, 1, 2, 3};
-#endif

while (1) {

@@ -116,7 +117,7 @@ static int lz4_uncompress(const char *source, char *dest, int osize)
/* copy repeated sequence */
if (unlikely((op - ref) < STEPSIZE)) {
#if LZ4_ARCH64
- size_t dec64 = dec64table[op - ref];
+ int dec64 = dec64table[op - ref];
#else
const int dec64 = 0;
#endif
@@ -174,11 +175,6 @@ static int lz4_uncompress_unknownoutputsize(const char *source, char *dest,
BYTE * const oend = op + maxoutputsize;
BYTE *cpy;

- size_t dec32table[] = {0, 3, 2, 3, 0, 0, 0, 0};
-#if LZ4_ARCH64
- size_t dec64table[] = {0, 0, 0, -1, 0, 1, 2, 3};
-#endif
-
/* Main Loop */
while (ip < iend) {

@@ -246,7 +242,7 @@ static int lz4_uncompress_unknownoutputsize(const char *source, char *dest,
/* copy repeated sequence */
if (unlikely((op - ref) < STEPSIZE)) {
#if LZ4_ARCH64
- size_t dec64 = dec64table[op - ref];
+ int dec64 = dec64table[op - ref];
#else
const int dec64 = 0;
#endif
--
2.1.3


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