[PATCH] glamor: Perform texture2D() separately from swizzle.

[Matt Turner]

The texture2D() happens in each branch, so we may as well do it as early
as possible and hide some of its latency in the branching instructions.
Moving it outside the (uniform) control flow reduces the number of
instructions in the fs_source shader from 64 to 46 and in the
set_alpha_source shader from 69 to 47 on Haswell.
---
Untested. Given a short primer on benchmarking glamor I'd be happy
to run some benchmarks.

 glamor/glamor_core.c | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/glamor/glamor_core.c b/glamor/glamor_core.c
index 737b274..a26f8f9 100644
--- a/glamor/glamor_core.c
+++ b/glamor/glamor_core.c
@@ -173,46 +173,48 @@ glamor_init_finish_access_shaders(ScreenPtr screen)
     const char *fs_source =
         "void main()\n"
         "{\n"
+        "   vec4 color = texture2D(sampler, source_texture);\n"
         "   if (revert == REVERT_NONE) \n"
         "    { \n"
         "     if ((swap_rb != SWAP_NONE_DOWNLOADING) && (swap_rb != SWAP_NONE_UPLOADING))   \n"
-        "	  	gl_FragColor = texture2D(sampler, source_texture).bgra;\n"
+        "		gl_FragColor = color.bgra;\n"
         "     else \n"
-        "	  	gl_FragColor = texture2D(sampler, source_texture).rgba;\n"
+        "		gl_FragColor = color.rgba;\n"
         "    } \n"
         "   else \n"
         "    { \n"
         "     if (swap_rb == SWAP_DOWNLOADING)   \n"
-        "	  	gl_FragColor = texture2D(sampler, source_texture).argb;\n"
+        "		gl_FragColor = color.argb;\n"
         "     else if (swap_rb == SWAP_NONE_DOWNLOADING)\n"
-        "	  	gl_FragColor = texture2D(sampler, source_texture).abgr;\n"
+        "		gl_FragColor = color.abgr;\n"
         "     else if (swap_rb == SWAP_UPLOADING)\n"
-        "	  	gl_FragColor = texture2D(sampler, source_texture).gbar;\n"
+        "		gl_FragColor = color.gbar;\n"
         "     else if (swap_rb == SWAP_NONE_UPLOADING)\n"
-        "	  	gl_FragColor = texture2D(sampler, source_texture).abgr;\n"
+        "		gl_FragColor = color.abgr;\n"
         "    } \n"
         "}\n";
 
     const char *set_alpha_source =
         "void main()\n"
         "{\n"
+        "   vec4 color = texture2D(sampler, source_texture);\n"
         "   if (revert == REVERT_NONE) \n"
         "    { \n"
         "     if ((swap_rb != SWAP_NONE_DOWNLOADING) && (swap_rb != SWAP_NONE_UPLOADING))   \n"
-        "	  	gl_FragColor = vec4(texture2D(sampler, source_texture).bgr, 1);\n"
+        "		gl_FragColor = vec4(color.bgr, 1);\n"
         "     else \n"
-        "	  	gl_FragColor = vec4(texture2D(sampler, source_texture).rgb, 1);\n"
+        "		gl_FragColor = vec4(color.rgb, 1);\n"
         "    } \n"
         "   else \n"
         "    { \n"
         "     if (swap_rb == SWAP_DOWNLOADING)   \n"
-        "	  	gl_FragColor = vec4(1, texture2D(sampler, source_texture).rgb);\n"
+        "		gl_FragColor = vec4(1, color.rgb);\n"
         "     else if (swap_rb == SWAP_NONE_DOWNLOADING)\n"
-        "	  	gl_FragColor = vec4(1, texture2D(sampler, source_texture).bgr);\n"
+        "		gl_FragColor = vec4(1, color.bgr);\n"
         "     else if (swap_rb == SWAP_UPLOADING)\n"
-        "	  	gl_FragColor = vec4(texture2D(sampler, source_texture).gba, 1);\n"
+        "		gl_FragColor = vec4(color.gba, 1);\n"
         "     else if (swap_rb == SWAP_NONE_UPLOADING)\n"
-        "	  	gl_FragColor = vec4(texture2D(sampler, source_texture).abg, 1);\n"
+        "		gl_FragColor = vec4(color.abg, 1);\n"
         "    } \n"
         "}\n";
     GLint fs_prog, vs_prog, avs_prog, set_alpha_prog;
-- 
2.0.5