glsl/i965: move lower_offset_array up to GLSL compiler level.

This lowering pass will be useful for gallium drivers as well, in order to support
the GL TG4 oddity that is textureGatherOffsets.

Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>
Signed-off-by: Dave Airlie <airlied@redhat.com>

src/glsl/lower_offset_array.cpp

@@ -0,0 +1,90 @@
+/*
+ * Copyright © 2013 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 brw_lower_offset_array.cpp
+ *
+ * IR lower pass to decompose ir_texture ir_tg4 with an array of offsets
+ * into four ir_tg4s with a single ivec2 offset, select the .w component of each,
+ * and return those four values packed into a gvec4.
+ *
+ * \author Chris Forbes <chrisf@ijw.co.nz>
+ */
+
+#include "glsl_types.h"
+#include "ir.h"
+#include "ir_builder.h"
+#include "ir_optimization.h"
+#include "ir_rvalue_visitor.h"
+
+using namespace ir_builder;
+
+class brw_lower_offset_array_visitor : public ir_rvalue_visitor {
+public:
+   brw_lower_offset_array_visitor()
+   {
+      progress = false;
+   }
+
+   void handle_rvalue(ir_rvalue **rv);
+
+   bool progress;
+};
+
+void
+brw_lower_offset_array_visitor::handle_rvalue(ir_rvalue **rv)
+{
+   if (*rv == NULL || (*rv)->ir_type != ir_type_texture)
+      return;
+
+   ir_texture *ir = (ir_texture *) *rv;
+   if (ir->op != ir_tg4 || !ir->offset || !ir->offset->type->is_array())
+      return;
+
+   void *mem_ctx = ralloc_parent(ir);
+
+   ir_variable *var = new (mem_ctx) ir_variable(ir->type, "result", ir_var_auto);
+   base_ir->insert_before(var);
+
+   for (int i = 0; i < 4; i++) {
+      ir_texture *tex = ir->clone(mem_ctx, NULL);
+      tex->offset = new (mem_ctx) ir_dereference_array(tex->offset,
+            new (mem_ctx) ir_constant(i));
+
+      base_ir->insert_before(assign(var, swizzle_w(tex), 1 << i));
+   }
+
+   *rv = new (mem_ctx) ir_dereference_variable(var);
+
+   progress = true;
+}
+
+bool
+lower_offset_arrays(exec_list *instructions)
+{
+   brw_lower_offset_array_visitor v;
+
+   visit_list_elements(&v, instructions);
+
+   return v.progress;
+}