[Mesa-dev] [PATCH] mesa: Optimize SWIZZLE_CONVERT_LOOP macro.

[Matt Turner]

Cuts about 1.5k of text size and reduces the compile time from 23~27 to
19 seconds.

   text    data     bss     dec     hex filename
 243337       0       0  243337   3b689 .libs/format_utils.o
 241807       0       0  241807   3b08f .libs/format_utils.o
---
Numbers from gcc-4.8.2 on an amd64 system. Hopefully this improves
compile time on x86 by a bunch more.

 src/mesa/main/format_utils.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/src/mesa/main/format_utils.c b/src/mesa/main/format_utils.c
index 240e3bc..b24e067 100644
--- a/src/mesa/main/format_utils.c
+++ b/src/mesa/main/format_utils.c
@@ -318,15 +318,19 @@ swizzle_convert_try_memcpy(void *dst, GLenum dst_type, int num_dst_channels,
          tmp[j] = CONV;                                           \
       }                                                           \
                                                                   \
-      typed_dst[0] = tmp[swizzle_x];                              \
-      if (DST_CHANS > 1) {                                        \
+      switch (4 - DST_CHANS) {                                    \
+      case 3:                                                     \
+         typed_dst[0] = tmp[swizzle_x];                           \
+         /* fallthrough */                                        \
+      case 2:                                                     \
          typed_dst[1] = tmp[swizzle_y];                           \
-         if (DST_CHANS > 2) {                                     \
-            typed_dst[2] = tmp[swizzle_z];                        \
-            if (DST_CHANS > 3) {                                  \
-               typed_dst[3] = tmp[swizzle_w];                     \
-            }                                                     \
-         }                                                        \
+         /* fallthrough */                                        \
+      case 1:                                                     \
+         typed_dst[2] = tmp[swizzle_z];                           \
+         /* fallthrough */                                        \
+      case 0:                                                     \
+         typed_dst[3] = tmp[swizzle_w];                           \
+         /* fallthrough */                                        \
       }                                                           \
       typed_src += SRC_CHANS;                                     \
       typed_dst += DST_CHANS;                                     \
-- 
1.8.5.5