[PATCH 1/6] make byte swapping macros less opaque to the optimizer

[Matt Turner]

Text size reduction of ~33k (1.8%):
   text	   data	    bss	    dec	    hex	filename
1879739	  72212	  55328	2007279	 1ea0ef	hw/xfree86/Xorg.before
1845291	  72212	  55328	1972831	 1e1a5f	hw/xfree86/Xorg

On x86[-64], the number of bswap instructions goes up from 5 to 1006.

By defining lswapl as gcc's builtin bswap32, the number of bswap
instructions used goes up to 1025, but the text and binary sizes stay
the same. This tells me that either gcc is
	- dumb, and unable to optimize away __builtin_bswap32 when it should
	- smart, and able to optimize away the open-coded bswap

Either way, it doesn't matter much.

Signed-off-by: Matt Turner <mattst88 at gmail.com>
---

The follow-up patch to this which removes the temporary variables used
by the swap macros is too big for the mailing list, so please review it
here:
http://cgit.freedesktop.org/~mattst88/xserver/commit/?id=11ff6813cf2f2a04243f4eecb60078d77fc973ec

I have compile tested ephyr and dmx, but I wasn't able to compile test
XQuartz, so please give it a test.

 include/misc.h |   31 ++++++++-----------------------
 1 files changed, 8 insertions(+), 23 deletions(-)

diff --git a/include/misc.h b/include/misc.h
index 803f5ba..b7a3fd2 100644
--- a/include/misc.h
+++ b/include/misc.h
@@ -240,32 +240,17 @@ xstrtokenize(const char *str, const char* separators);
 #define SwapRestL(stuff) \
     SwapLongs((CARD32 *)(stuff + 1), LengthRestL(stuff))
 
-/* byte swap a 32-bit value */
-#define swapl(x, n) { \
-		 n = ((char *) (x))[0];\
-		 ((char *) (x))[0] = ((char *) (x))[3];\
-		 ((char *) (x))[3] = n;\
-		 n = ((char *) (x))[1];\
-		 ((char *) (x))[1] = ((char *) (x))[2];\
-		 ((char *) (x))[2] = n; }
-
-/* byte swap a short */
-#define swaps(x, n) { \
-		 n = ((char *) (x))[0];\
-		 ((char *) (x))[0] = ((char *) (x))[1];\
-		 ((char *) (x))[1] = n; }
-
 /* copy 32-bit value from src to dst byteswapping on the way */
-#define cpswapl(src, dst) { \
-                 ((char *)&(dst))[0] = ((char *) &(src))[3];\
-                 ((char *)&(dst))[1] = ((char *) &(src))[2];\
-                 ((char *)&(dst))[2] = ((char *) &(src))[1];\
-                 ((char *)&(dst))[3] = ((char *) &(src))[0]; }
+#define cpswapl(src, dst) (dst) = lswapl((src))
 
 /* copy short from src to dst byteswapping on the way */
-#define cpswaps(src, dst) { \
-		 ((char *) &(dst))[0] = ((char *) &(src))[1];\
-		 ((char *) &(dst))[1] = ((char *) &(src))[0]; }
+#define cpswaps(src, dst) (dst) = lswaps((src))
+
+/* byte swap a 32-bit value */
+#define swapl(x, n) (*(x)) = lswapl(*(x))
+
+/* byte swap a short */
+#define swaps(x, n) (*(x)) = lswaps(*(x))
 
 extern _X_EXPORT void SwapLongs(
     CARD32 *list,
-- 
1.7.3.4