[Xen-devel] [PATCH 2/3] lz4: pull out constant tables

[Jan Beulich <jbeulich@xxxxxxxx>]

From: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxxxxx>
[Linux commit bea2b592fd18eb8ffa3fc4ad380610632d03a38f]

Use {,u}int8_t instead of plain "int" for the tables.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/common/lz4/decompress.c
+++ b/xen/common/lz4/decompress.c
@@ -39,6 +39,11 @@
 
 #include "defs.h"
 
+static const uint8_t dec32table[] = {0, 3, 2, 3, 0, 0, 0, 0};
+#if LZ4_ARCH64
+static const int8_t dec64table[] = {0, 0, 0, -1, 0, 1, 2, 3};
+#endif
+
 #if defined(__XEN__) || defined(__MINIOS__)
 
 static int INIT lz4_uncompress(const unsigned char *source, unsigned char 
*dest,
@@ -51,10 +56,6 @@ static int INIT lz4_uncompress(const uns
        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) {
 
@@ -109,7 +110,7 @@ static int INIT lz4_uncompress(const uns
                /* 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
@@ -175,11 +176,6 @@ static int lz4_uncompress_unknownoutputs
        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) {
 
@@ -245,7 +241,7 @@ static int lz4_uncompress_unknownoutputs
                /* 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


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