nir: Try to make sense of the nir_shader_compiler_options code.

The code in glsl_to_nir is entirely dead, as we translate from GLSL to
NIR at link time, when there isn't a _mesa_glsl_parse_state to pass,
so every caller passes NULL.

glsl_to_nir seems like the wrong place to try and create the shader
compiler options structure anyway - tgsi_to_nir, prog_to_nir, and other
translators all would have to duplicate that code.  The driver should
set this up once with whatever settings it wants, and pass it in.

Eric also added a NirOptions field to ctx->Const.ShaderCompilerOptions[]
and left a comment saying: "The memory for the options is expected to be
kept in a single static copy by the driver."  This suggests the plan was
to do exactly that.  That pointer was not marked const, however, and the
dead code used a mix of static structures and ralloced ones.

This patch deletes the dead code in glsl_to_nir, instead making it take
the shader compiler options as a mandatory argument.  It creates an
(empty) options struct in the i965 driver, and makes NirOptions point
to that.  It marks the pointer const so that we can actually do so
without generating "discards const qualifier" compiler warnings.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Acked-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>

src/glsl/nir/glsl_to_nir.cpp

@@ -124,34 +124,10 @@ private:
 
 }; /* end of anonymous namespace */
 
-static const nir_shader_compiler_options default_options = {
-};
-
 nir_shader *
-glsl_to_nir(exec_list *ir, _mesa_glsl_parse_state *state,
-            bool native_integers)
+glsl_to_nir(exec_list *ir, bool native_integers,
+            const nir_shader_compiler_options *options)
 {
-   const nir_shader_compiler_options *options;
-
-   if (state) {
-      struct gl_context *ctx = state->ctx;
-      struct gl_shader_compiler_options *gl_options =
-         &ctx->Const.ShaderCompilerOptions[state->stage];
-
-      if (!gl_options->NirOptions) {
-         nir_shader_compiler_options *new_options =
-            rzalloc(ctx, nir_shader_compiler_options);
-         options = gl_options->NirOptions = new_options;
-
-         if (gl_options->EmitNoPow)
-            new_options->lower_fpow = true;
-      } else {
-         options = gl_options->NirOptions;
-      }
-   } else {
-      options = &default_options;
-   }
-
    nir_shader *shader = nir_shader_create(NULL, options);
 
    nir_visitor v1(shader, native_integers);

src/glsl/nir/glsl_to_nir.h

@@ -32,8 +32,8 @@
 extern "C" {
 #endif
 
-nir_shader *glsl_to_nir(exec_list * ir, _mesa_glsl_parse_state *state,
-                        bool native_integers);
+nir_shader *glsl_to_nir(exec_list *ir, bool native_integers,
+                        const nir_shader_compiler_options *options);
 
 #ifdef __cplusplus
 }

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

@@ -68,6 +68,8 @@
 #include "tnl/t_pipeline.h"
 #include "util/ralloc.h"
 
+#include "glsl/nir/nir.h"
+
 /***************************************
  * Mesa's Driver Functions
  ***************************************/
@@ -549,6 +551,8 @@ brw_initialize_context_constants(struct brw_context *brw)
       ctx->Const.Program[MESA_SHADER_FRAGMENT].MaxInputComponents = 128;
    }
 
+   static const nir_shader_compiler_options nir_options = {};
+
    /* We want the GLSL compiler to emit code that uses condition codes */
    for (int i = 0; i < MESA_SHADER_STAGES; i++) {
       ctx->Const.ShaderCompilerOptions[i].MaxIfDepth = brw->gen < 6 ? 16 : UINT_MAX;
@@ -562,6 +566,7 @@ brw_initialize_context_constants(struct brw_context *brw)
 	 (i == MESA_SHADER_FRAGMENT);
       ctx->Const.ShaderCompilerOptions[i].EmitNoIndirectUniform = false;
       ctx->Const.ShaderCompilerOptions[i].LowerClipDistance = true;
+      ctx->Const.ShaderCompilerOptions[i].NirOptions = &nir_options;
    }
 
    ctx->Const.ShaderCompilerOptions[MESA_SHADER_VERTEX].OptimizeForAOS = true;

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

@@ -82,9 +82,12 @@ count_nir_instrs(nir_shader *nir)
 void
 fs_visitor::emit_nir_code()
 {
+   const nir_shader_compiler_options *options =
+      ctx->Const.ShaderCompilerOptions[stage].NirOptions;
+
    /* first, lower the GLSL IR shader to NIR */
    lower_output_reads(shader->base.ir);
-   nir_shader *nir = glsl_to_nir(shader->base.ir, NULL, true);
+   nir_shader *nir = glsl_to_nir(shader->base.ir, true, options);
    nir_validate_shader(nir);
 
    nir_lower_global_vars_to_local(nir);

src/mesa/main/mtypes.h

@@ -3036,7 +3036,7 @@ struct gl_shader_compiler_options
 
    struct gl_sl_pragmas DefaultPragmas; /**< Default #pragma settings */
 
-   struct nir_shader_compiler_options *NirOptions;
+   const struct nir_shader_compiler_options *NirOptions;
 };