glsl: Add a lowering pass for gl_VertexID

Converts gl_VertexID to (gl_VertexIDMESA + gl_BaseVertex). gl_VertexIDMESA
is backed by SYSTEM_VALUE_VERTEX_ID_ZERO_BASE, and gl_BaseVertex is backed
by SYSTEM_VALUE_BASE_VERTEX.

v2: Put the enum in struct gl_constants and propoerly resolve the scope
in C++ code.  Fix suggested by Marek.

v3: Reabase on Matt's foreach_in_list changes (was using foreach_list).

v4 (Ken): Use a systemvalue instead of a uniform because
STATE_BASE_VERTEX has been removed.

v5: Use a boolean to select lowering, and only allow one lowering
method.  Suggested by Ken.

v6 (Ken): Replace strcmp against literal "gl_BaseVertex"/"gl_VertexID"
with SYSTEM_VALUE enum checks, for efficiency.

v7: Rebase on context constant initialization work.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>

src/glsl/Makefile.sources

@@ -76,6 +76,7 @@ LIBGLSL_FILES = \
 	$(GLSL_SRCDIR)/lower_vec_index_to_swizzle.cpp \
 	$(GLSL_SRCDIR)/lower_vector.cpp \
 	$(GLSL_SRCDIR)/lower_vector_insert.cpp \
+	$(GLSL_SRCDIR)/lower_vertex_id.cpp \
 	$(GLSL_SRCDIR)/lower_output_reads.cpp \
 	$(GLSL_SRCDIR)/lower_ubo_reference.cpp \
 	$(GLSL_SRCDIR)/opt_algebraic.cpp \

src/glsl/ir_optimization.h

@@ -126,6 +126,8 @@ bool optimize_redundant_jumps(exec_list *instructions);
 bool optimize_split_arrays(exec_list *instructions, bool linked);
 bool lower_offset_arrays(exec_list *instructions);
 
+bool lower_vertex_id(gl_shader *shader);
+
 ir_rvalue *
 compare_index_block(exec_list *instructions, ir_variable *index,
 		    unsigned base, unsigned components, void *mem_ctx);

src/glsl/linker.cpp

@@ -1737,6 +1737,9 @@ link_intrastage_shaders(void *mem_ctx,
       }
    }
 
+   if (ctx->Const.VertexID_is_zero_based)
+      lower_vertex_id(linked);
+
    /* Make a pass over all variable declarations to ensure that arrays with
     * unspecified sizes have a size specified.  The size is inferred from the
     * max_array_access field.

src/glsl/lower_vertex_id.cpp

@@ -0,0 +1,144 @@
+/*
+ * Copyright © 2014 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+/**
+ * \file lower_vertex_id.cpp
+ *
+ * There exists hardware, such as i965, that does not implement the OpenGL
+ * semantic for gl_VertexID.  Instead, that hardware does not include the
+ * value of basevertex in the gl_VertexID value.  To implement the OpenGL
+ * semantic, we'll have to convert gl_Vertex_ID to
+ * gl_VertexIDMESA+gl_BaseVertexMESA.
+ */
+
+#include "glsl_symbol_table.h"
+#include "ir_hierarchical_visitor.h"
+#include "ir.h"
+#include "ir_builder.h"
+#include "linker.h"
+#include "program/prog_statevars.h"
+
+namespace {
+
+class lower_vertex_id_visitor : public ir_hierarchical_visitor {
+public:
+   explicit lower_vertex_id_visitor(ir_function_signature *main_sig,
+                                    exec_list *ir_list)
+      : progress(false), VertexID(NULL), gl_VertexID(NULL),
+        gl_BaseVertex(NULL), main_sig(main_sig), ir_list(ir_list)
+   {
+      foreach_in_list(ir_instruction, ir, ir_list) {
+         ir_variable *const var = ir->as_variable();
+
+         if (var != NULL && var->data.mode == ir_var_system_value &&
+             var->data.location == SYSTEM_VALUE_BASE_VERTEX) {
+            gl_BaseVertex = var;
+            break;
+         }
+      }
+   }
+
+   virtual ir_visitor_status visit(ir_dereference_variable *);
+
+   bool progress;
+
+private:
+   ir_variable *VertexID;
+   ir_variable *gl_VertexID;
+   ir_variable *gl_BaseVertex;
+
+   ir_function_signature *main_sig;
+   exec_list *ir_list;
+};
+
+} /* anonymous namespace */
+
+ir_visitor_status
+lower_vertex_id_visitor::visit(ir_dereference_variable *ir)
+{
+   if (ir->var->data.mode != ir_var_system_value ||
+       ir->var->data.location != SYSTEM_VALUE_VERTEX_ID)
+      return visit_continue;
+
+   if (VertexID == NULL) {
+      const glsl_type *const int_t = glsl_type::int_type;
+      void *const mem_ctx = ralloc_parent(ir);
+
+      VertexID = new(mem_ctx) ir_variable(int_t, "__VertexID",
+                                          ir_var_temporary);
+      ir_list->push_head(VertexID);
+
+      gl_VertexID = new(mem_ctx) ir_variable(int_t, "gl_VertexIDMESA",
+                                             ir_var_system_value);
+      gl_VertexID->data.how_declared = ir_var_declared_implicitly;
+      gl_VertexID->data.read_only = true;
+      gl_VertexID->data.location = SYSTEM_VALUE_VERTEX_ID_ZERO_BASE;
+      gl_VertexID->data.explicit_location = true;
+      gl_VertexID->data.explicit_index = 0;
+      ir_list->push_head(gl_VertexID);
+
+      if (gl_BaseVertex == NULL) {
+         gl_BaseVertex = new(mem_ctx) ir_variable(int_t, "gl_BaseVertex",
+                                                  ir_var_system_value);
+         gl_BaseVertex->data.how_declared = ir_var_declared_implicitly;
+         gl_BaseVertex->data.read_only = true;
+         gl_BaseVertex->data.location = SYSTEM_VALUE_BASE_VERTEX;
+         gl_BaseVertex->data.explicit_location = true;
+         gl_BaseVertex->data.explicit_index = 0;
+         ir_list->push_head(gl_BaseVertex);
+      }
+
+      ir_instruction *const inst =
+         ir_builder::assign(VertexID,
+                            ir_builder::add(gl_VertexID, gl_BaseVertex));
+
+      main_sig->body.push_head(inst);
+   }
+
+   ir->var = VertexID;
+   progress = true;
+
+   return visit_continue;
+}
+
+bool
+lower_vertex_id(gl_shader *shader)
+{
+   /* gl_VertexID only exists in the vertex shader.
+    */
+   if (shader->Stage != MESA_SHADER_VERTEX)
+      return false;
+
+   ir_function_signature *const main_sig =
+      link_get_main_function_signature(shader);
+   if (main_sig == NULL) {
+      assert(main_sig != NULL);
+      return false;
+   }
+
+   lower_vertex_id_visitor v(main_sig, shader->ir);
+
+   v.run(shader->ir);
+
+   return v.progress;
+}

src/mesa/main/context.c

@@ -622,6 +622,12 @@ _mesa_init_constants(struct gl_constants *consts, gl_api api)
    consts->MaxProgramMatrices = MAX_PROGRAM_MATRICES;
    consts->MaxProgramMatrixStackDepth = MAX_PROGRAM_MATRIX_STACK_DEPTH;
 
+   /* Assume that if GLSL 1.30+ (or GLSL ES 3.00+) is supported that
+    * gl_VertexID is implemented using a native hardware register with OpenGL
+    * semantics.
+    */
+   consts->VertexID_is_zero_based = false;
+
    /* CheckArrayBounds is overriden by drivers/x11 for X server */
    consts->CheckArrayBounds = GL_FALSE;
 

src/mesa/main/mtypes.h

@@ -3487,6 +3487,15 @@ struct gl_constants
     */
    GLboolean NativeIntegers;
 
+   /**
+    * Does VertexID count from zero or from base vertex?
+    *
+    * \note
+    * If desktop GLSL 1.30 or GLSL ES 3.00 are not supported, this field is
+    * ignored and need not be set.
+    */
+   bool VertexID_is_zero_based;
+
    /**
     * If the driver supports real 32-bit integers, what integer value should be
     * used for boolean true in uniform uploads?  (Usually 1 or ~0.)