glsl: Vectorize multiple scalar assignments

Reduces vertex shader instruction counts in DOTA2 by 6.42%, L4D2 by
4.61%, and CS:GO by 5.71%.

total instructions in shared programs: 1500153 -> 1498191 (-0.13%)
instructions in affected programs:     59919 -> 57957 (-3.27%)

Reviewed-by: Ian Romanick <[email protected]>

1 files changed, 319 insertions, 0 deletions

diff --git a/src/glsl/opt_vectorize.cpp b/src/glsl/opt_vectorize.cpp
new file mode 100644
index 00000000000..9ca811a8603
--- /dev/null
+++ b/src/glsl/opt_vectorize.cpp
@@ -0,0 +1,319 @@
+/*
+ * 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 opt_vectorize.cpp
+ *
+ * Combines scalar assignments of the same expression (modulo swizzle) to
+ * multiple channels of the same variable into a single vectorized expression
+ * and assignment.
+ *
+ * Many generated shaders contain scalarized code. That is, they contain
+ *
+ * r1.x = log2(v0.x);
+ * r1.y = log2(v0.y);
+ * r1.z = log2(v0.z);
+ *
+ * rather than
+ *
+ * r1.xyz = log2(v0.xyz);
+ *
+ * We look for consecutive assignments of the same expression (modulo swizzle)
+ * to each channel of the same variable.
+ *
+ * For instance, we want to convert these three scalar operations
+ *
+ * (assign (x) (var_ref r1) (expression float log2 (swiz x (var_ref v0))))
+ * (assign (y) (var_ref r1) (expression float log2 (swiz y (var_ref v0))))
+ * (assign (z) (var_ref r1) (expression float log2 (swiz z (var_ref v0))))
+ *
+ * into a single vector operation
+ *
+ * (assign (xyz) (var_ref r1) (expression vec3 log2 (swiz xyz (var_ref v0))))
+ */
+
+#include "ir.h"
+#include "ir_visitor.h"
+#include "ir_optimization.h"
+#include "glsl_types.h"
+#include "program/prog_instruction.h"
+
+namespace {
+
+class ir_vectorize_visitor : public ir_hierarchical_visitor {
+public:
+   void clear()
+   {
+      assignment[0] = NULL;
+      assignment[1] = NULL;
+      assignment[2] = NULL;
+      assignment[3] = NULL;
+      current_assignment = NULL;
+      last_assignment = NULL;
+      channels = 0;
+      has_swizzle = false;
+   }
+
+   ir_vectorize_visitor()
+   {
+      clear();
+      progress = false;
+   }
+
+   virtual ir_visitor_status visit_enter(ir_assignment *);
+   virtual ir_visitor_status visit_enter(ir_swizzle *);
+
+   virtual ir_visitor_status visit_leave(ir_assignment *);
+
+   void try_vectorize();
+
+   ir_assignment *assignment[4];
+   ir_assignment *current_assignment, *last_assignment;
+   unsigned channels;
+   bool has_swizzle;
+
+   bool progress;
+};
+
+} /* unnamed namespace */
+
+/**
+ * Rewrites the swizzles and types of a right-hand side of an assignment.
+ *
+ * From the example above, this function would be called (by visit_tree()) on
+ * the nodes of the tree (expression float log2 (swiz z   (var_ref v0))),
+ * rewriting it into     (expression vec3  log2 (swiz xyz (var_ref v0))).
+ *
+ * The function modifies only ir_expressions and ir_swizzles. For expressions
+ * it sets a new type and swizzles any scalar dereferences into appropriately
+ * sized vector arguments. For example, if combining
+ *
+ * (assign (x) (var_ref r1) (expression float + (swiz x (var_ref v0) (var_ref v1))))
+ * (assign (y) (var_ref r1) (expression float + (swiz y (var_ref v0) (var_ref v1))))
+ *
+ * where v1 is a scalar, rewrite_swizzle() would insert a swizzle on
+ * (var_ref v1) such that the final result was
+ *
+ * (assign (xy) (var_ref r1) (expression vec2 + (swiz xy (var_ref v0))
+ *                                              (swiz xx (var_ref v1))))
+ *
+ * For swizzles, it sets a new type, and if the variable being swizzled is a
+ * vector it overwrites the swizzle mask with the ir_swizzle_mask passed as the
+ * data parameter. If the swizzled variable is scalar, then the swizzle was
+ * added by an earlier call to rewrite_swizzle() on an expression, so the
+ * mask should not be modified.
+ */
+static void
+rewrite_swizzle(ir_instruction *ir, void *data)
+{
+   ir_swizzle_mask *mask = (ir_swizzle_mask *)data;
+
+   switch (ir->ir_type) {
+   case ir_type_swizzle: {
+      ir_swizzle *swz = (ir_swizzle *)ir;
+      if (swz->val->type->is_vector()) {
+         swz->mask = *mask;
+      }
+      swz->type = glsl_type::get_instance(swz->type->base_type,
+                                          mask->num_components, 1);
+      break;
+   }
+   case ir_type_expression: {
+      ir_expression *expr = (ir_expression *)ir;
+      expr->type = glsl_type::get_instance(expr->type->base_type,
+                                           mask->num_components, 1);
+      for (unsigned i = 0; i < 4; i++) {
+         if (expr->operands[i]) {
+            ir_dereference *deref = expr->operands[i]->as_dereference();
+            if (deref && deref->type->is_scalar()) {
+               expr->operands[i] = new(ir) ir_swizzle(deref, 0, 0, 0, 0,
+                                                      mask->num_components);
+            }
+         }
+      }
+      break;
+   }
+   default:
+      break;
+   }
+}
+
+/**
+ * Attempt to vectorize the previously saved assignments, and clear them from
+ * consideration.
+ *
+ * If the assignments are able to be combined, it modifies in-place the last
+ * assignment seen to be an equivalent vector form of the scalar assignments.
+ * It then removes the other now obsolete scalar assignments.
+ */
+void
+ir_vectorize_visitor::try_vectorize()
+{
+   if (this->last_assignment && this->channels > 1) {
+      ir_swizzle_mask mask = {0, 1, 2, 3, channels, 0};
+
+      visit_tree(this->last_assignment->rhs, rewrite_swizzle, &mask);
+
+      this->last_assignment->write_mask = 0;
+
+      for (unsigned i = 0; i < 4; i++) {
+         if (this->assignment[i]) {
+            this->last_assignment->write_mask |= 1 << i;
+
+            if (this->assignment[i] != this->last_assignment) {
+               this->assignment[i]->remove();
+            }
+         }
+      }
+
+      this->progress = true;
+   }
+   clear();
+}
+
+/**
+ * Returns whether the write mask is a single channel.
+ */
+static bool
+single_channel_write_mask(unsigned write_mask)
+{
+   return write_mask != 0 && (write_mask & (write_mask - 1)) == 0;
+}
+
+/**
+ * Translates single-channeled write mask to single-channeled swizzle.
+ */
+static unsigned
+write_mask_to_swizzle(unsigned write_mask)
+{
+   switch (write_mask) {
+   case WRITEMASK_X: return SWIZZLE_X;
+   case WRITEMASK_Y: return SWIZZLE_Y;
+   case WRITEMASK_Z: return SWIZZLE_Z;
+   case WRITEMASK_W: return SWIZZLE_W;
+   }
+   assert(!"not reached");
+   unreachable();
+}
+
+/**
+ * Returns whether a single-channeled write mask matches a swizzle.
+ */
+static bool
+write_mask_matches_swizzle(unsigned write_mask,
+                           const ir_swizzle *swz)
+{
+   return ((write_mask == WRITEMASK_X && swz->mask.x == SWIZZLE_X) ||
+           (write_mask == WRITEMASK_Y && swz->mask.x == SWIZZLE_Y) ||
+           (write_mask == WRITEMASK_Z && swz->mask.x == SWIZZLE_Z) ||
+           (write_mask == WRITEMASK_W && swz->mask.x == SWIZZLE_W));
+}
+
+/**
+ * Upon entering an ir_assignment, attempt to vectorize the currently tracked
+ * assignments if the current assignment is not suitable. Keep a pointer to
+ * the current assignment.
+ */
+ir_visitor_status
+ir_vectorize_visitor::visit_enter(ir_assignment *ir)
+{
+   ir_dereference *lhs = this->last_assignment != NULL ?
+                         this->last_assignment->lhs : NULL;
+   ir_rvalue *rhs = this->last_assignment != NULL ?
+                    this->last_assignment->rhs : NULL;
+
+   if (ir->condition ||
+       this->channels >= 4 ||
+       !single_channel_write_mask(ir->write_mask) ||
+       (lhs && !ir->lhs->equals(lhs)) ||
+       (rhs && !ir->rhs->equals(rhs, ir_type_swizzle))) {
+      try_vectorize();
+   }
+
+   this->current_assignment = ir;
+
+   return visit_continue;
+}
+
+/**
+ * Upon entering an ir_swizzle, set ::has_swizzle if we're visiting from an
+ * ir_assignment (i.e., that ::current_assignment is set) and the swizzle mask
+ * matches the current assignment's write mask.
+ *
+ * If the write mask doesn't match the swizzle mask, remove the current
+ * assignment from further consideration.
+ */
+ir_visitor_status
+ir_vectorize_visitor::visit_enter(ir_swizzle *ir)
+{
+   if (this->current_assignment) {
+      if (write_mask_matches_swizzle(this->current_assignment->write_mask, ir)) {
+         this->has_swizzle = true;
+      } else {
+         this->current_assignment = NULL;
+      }
+   }
+   return visit_continue;
+}
+
+/**
+ * Upon leaving an ir_assignment, save a pointer to it in ::assignment[] if
+ * the swizzle mask(s) found were appropriate. Also save a pointer in
+ * ::last_assignment so that we can compare future assignments with it.
+ *
+ * Finally, clear ::current_assignment and ::has_swizzle.
+ */
+ir_visitor_status
+ir_vectorize_visitor::visit_leave(ir_assignment *ir)
+{
+   if (this->has_swizzle && this->current_assignment) {
+      assert(this->current_assignment == ir);
+
+      unsigned channel = write_mask_to_swizzle(this->current_assignment->write_mask);
+      this->assignment[channel] = ir;
+      this->channels++;
+
+      this->last_assignment = this->current_assignment;
+   }
+   this->current_assignment = NULL;
+   this->has_swizzle = false;
+   return visit_continue;
+}
+
+/**
+ * Combines scalar assignments of the same expression (modulo swizzle) to
+ * multiple channels of the same variable into a single vectorized expression
+ * and assignment.
+ */
+bool
+do_vectorize(exec_list *instructions)
+{
+   ir_vectorize_visitor v;
+
+   v.run(instructions);
+
+   /* Try to vectorize the last assignments seen. */
+   v.try_vectorize();
+
+   return v.progress;
+}