mesa: add gl_constants::GLSLOptimizeConservatively

to reduce the amount of GLSL optimizations for drivers that can do better.

Reviewed-by: Eric Anholt <eric@anholt.net>

src/compiler/glsl/glsl_parser_extras.cpp

@@ -1949,12 +1949,20 @@ _mesa_glsl_compile_shader(struct gl_context *ctx, struct gl_shader *shader,
 
       assign_subroutine_indexes(shader, state);
       lower_subroutine(shader->ir, state);
+
       /* Do some optimization at compile time to reduce shader IR size
        * and reduce later work if the same shader is linked multiple times
        */
+      if (ctx->Const.GLSLOptimizeConservatively) {
+         /* Run it just once. */
+         do_common_optimization(shader->ir, false, false, options,
+                                ctx->Const.NativeIntegers);
+      } else {
+         /* Repeat it until it stops making changes. */
          while (do_common_optimization(shader->ir, false, false, options,
                                        ctx->Const.NativeIntegers))
             ;
+      }
 
       validate_ir_tree(shader->ir);
 

src/compiler/glsl/linker.cpp

@@ -5048,10 +5048,18 @@ link_shaders(struct gl_context *ctx, struct gl_shader_program *prog)
          lower_tess_level(prog->_LinkedShaders[i]);
       }
 
+      if (ctx->Const.GLSLOptimizeConservatively) {
+         /* Run it just once. */
+         do_common_optimization(prog->_LinkedShaders[i]->ir, true, false,
+                                &ctx->Const.ShaderCompilerOptions[i],
+                                ctx->Const.NativeIntegers);
+      } else {
+         /* Repeat it until it stops making changes. */
          while (do_common_optimization(prog->_LinkedShaders[i]->ir, true, false,
                                        &ctx->Const.ShaderCompilerOptions[i],
                                        ctx->Const.NativeIntegers))
             ;
+      }
 
       lower_const_arrays_to_uniforms(prog->_LinkedShaders[i]->ir, i);
       propagate_invariance(prog->_LinkedShaders[i]->ir);

src/mesa/main/ff_fragment_shader.cpp

@@ -1254,9 +1254,13 @@ create_new_program(struct gl_context *ctx, struct state_key *key)
    const struct gl_shader_compiler_options *options =
       &ctx->Const.ShaderCompilerOptions[MESA_SHADER_FRAGMENT];
 
+   /* Conservative approach: Don't optimize here, the linker does it too. */
+   if (!ctx->Const.GLSLOptimizeConservatively) {
       while (do_common_optimization(p.shader->ir, false, false, options,
                                     ctx->Const.NativeIntegers))
          ;
+   }
+
    reparent_ir(p.shader->ir, p.shader->ir);
 
    p.shader->CompileStatus = true;

src/mesa/main/mtypes.h

@@ -3642,6 +3642,13 @@ struct gl_constants
    bool GLSLFragCoordIsSysVal;
    bool GLSLFrontFacingIsSysVal;
 
+   /**
+    * Run the minimum amount of GLSL optimizations to be able to link
+    * shaders optimally (eliminate dead varyings and uniforms) and just do
+    * all the necessary lowering.
+    */
+   bool GLSLOptimizeConservatively;
+
    /**
     * Always use the GetTransformFeedbackVertexCount() driver hook, rather
     * than passing the transform feedback object to the drawing function.