i965: Don't perform the precompile on fragment shaders by default.

It is useful to have this option for shader-db, and it was also good
at the time where we were rejecting shaders due to various internal
limits we hadn't supported yet.  However, at this point the precompile
step takes extra time (since not all NOS is known at link time) and
spews misleading debug in the common case of debugging a real app.

This is left in place for VS, where we still have a couple of codegen
failure paths that result in link failure through precompile.  Those
need to be fixed.

shader-db can still get at the debug info it wants using
"shader_precompile=true" driconf option.  Long term, we can probably
build a good-enough app for shader-db to trigger real codegen.

src/mesa/drivers/dri/i965/brw_context.c

@@ -327,6 +327,7 @@ brwCreateContext(int api,
    brw_draw_init( brw );
 
    brw->new_vs_backend = (getenv("INTEL_OLD_VS") == NULL);
+   brw->precompile = driQueryOptionb(&intel->optionCache, "shader_precompile");
 
    /* If we're using the new shader backend, we require integer uniforms
     * stored as actual integers.

src/mesa/drivers/dri/i965/brw_context.h

@@ -604,6 +604,7 @@ struct brw_context
    bool has_aa_line_parameters;
    bool has_pln;
    bool new_vs_backend;
+   bool precompile;
 
    struct {
       struct brw_state_flags dirty;

src/mesa/drivers/dri/i965/brw_shader.cpp

@@ -65,7 +65,9 @@ brw_new_shader_program(struct gl_context *ctx, GLuint name)
 bool
 brw_shader_precompile(struct gl_context *ctx, struct gl_shader_program *prog)
 {
-   if (!brw_fs_precompile(ctx, prog))
+   struct brw_context *brw = brw_context(ctx);
+
+   if (brw->precompile && !brw_fs_precompile(ctx, prog))
       return false;
 
    if (!brw_vs_precompile(ctx, prog))

src/mesa/drivers/dri/intel/intel_screen.c

@@ -76,10 +76,14 @@ PUBLIC const char __driConfigOptions[] =
       DRI_CONF_OPT_BEGIN(stub_occlusion_query, bool, false)
 	 DRI_CONF_DESC(en, "Enable stub ARB_occlusion_query support on 915/945.")
       DRI_CONF_OPT_END
+
+      DRI_CONF_OPT_BEGIN(shader_precompile, bool, false)
+	 DRI_CONF_DESC(en, "Perform code generation at shader link time.")
+      DRI_CONF_OPT_END
    DRI_CONF_SECTION_END
 DRI_CONF_END;
 
-const GLuint __driNConfigOptions = 11;
+const GLuint __driNConfigOptions = 12;
 
 #include "intel_batchbuffer.h"
 #include "intel_buffers.h"