glsl: Create a _mesa_shader_stage_to_abbrev() function.

This is similar to _mesa_shader_stage_to_string(), but returns "VS"
instead of "vertex".

v2: Use unreachable() and add MESA_SHADER_COMPUTE (requested by Ian).

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>

src/glsl/glsl_parser_extras.cpp

@@ -376,6 +376,23 @@ _mesa_shader_stage_to_string(unsigned stage)
    return "unknown";
 }
 
+/**
+ * Translate a gl_shader_stage to a shader stage abbreviation (VS, GS, FS)
+ * for debug printouts and error messages.
+ */
+const char *
+_mesa_shader_stage_to_abbrev(unsigned stage)
+{
+   switch (stage) {
+   case MESA_SHADER_VERTEX:   return "VS";
+   case MESA_SHADER_FRAGMENT: return "FS";
+   case MESA_SHADER_GEOMETRY: return "GS";
+   case MESA_SHADER_COMPUTE:  return "CS";
+   }
+
+   unreachable("Unknown shader stage.");
+}
+
 /* This helper function will append the given message to the shader's
    info log and report it via GL_ARB_debug_output. Per that extension,
    'type' is one of the enum values classifying the message, and

src/glsl/glsl_parser_extras.h

@@ -583,6 +583,9 @@ extern "C" {
 extern const char *
 _mesa_shader_stage_to_string(unsigned stage);
 
+extern const char *
+_mesa_shader_stage_to_abbrev(unsigned stage);
+
 extern int glcpp_preprocess(void *ctx, const char **shader, char **info_log,
                       const struct gl_extensions *extensions, struct gl_context *gl_ctx);