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+/*
+ * 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 opt_minmax.cpp
+ *
+ * Drop operands from an expression tree of only min/max operations if they
+ * can be proven to not contribute to the final result.
+ *
+ * The algorithm is similar to alpha-beta pruning on a minmax search.
+ */
+
+#include "ir.h"
+#include "ir_visitor.h"
+#include "ir_rvalue_visitor.h"
+#include "ir_optimization.h"
+#include "ir_builder.h"
+#include "program/prog_instruction.h"
+#include "compiler/glsl_types.h"
+#include "main/macros.h"
+
+using namespace ir_builder;
+
+namespace {
+
+enum compare_components_result {
+ LESS,
+ LESS_OR_EQUAL,
+ EQUAL,
+ GREATER_OR_EQUAL,
+ GREATER,
+ MIXED
+};
+
+class minmax_range {
+public:
+ minmax_range(ir_constant *low = NULL, ir_constant *high = NULL)
+ {
+ this->low = low;
+ this->high = high;
+ }
+
+ /* low is the lower limit of the range, high is the higher limit. NULL on
+ * low means negative infinity (unlimited) and on high positive infinity
+ * (unlimited). Because of the two interpretations of the value NULL,
+ * arbitrary comparison between ir_constants is impossible.
+ */
+ ir_constant *low;
+ ir_constant *high;
+};
+
+class ir_minmax_visitor : public ir_rvalue_enter_visitor {
+public:
+ ir_minmax_visitor()
+ : progress(false)
+ {
+ }
+
+ ir_rvalue *prune_expression(ir_expression *expr, minmax_range baserange);
+
+ void handle_rvalue(ir_rvalue **rvalue);
+
+ bool progress;
+};
+
+/*
+ * Returns LESS if all vector components of `a' are strictly lower than of `b',
+ * GREATER if all vector components of `a' are strictly greater than of `b',
+ * MIXED if some vector components of `a' are strictly lower than of `b' while
+ * others are strictly greater, or EQUAL otherwise.
+ */
+static enum compare_components_result
+compare_components(ir_constant *a, ir_constant *b)
+{
+ assert(a != NULL);
+ assert(b != NULL);
+
+ assert(a->type->base_type == b->type->base_type);
+
+ unsigned a_inc = a->type->is_scalar() ? 0 : 1;
+ unsigned b_inc = b->type->is_scalar() ? 0 : 1;
+ unsigned components = MAX2(a->type->components(), b->type->components());
+
+ bool foundless = false;
+ bool foundgreater = false;
+ bool foundequal = false;
+
+ for (unsigned i = 0, c0 = 0, c1 = 0;
+ i < components;
+ c0 += a_inc, c1 += b_inc, ++i) {
+ switch (a->type->base_type) {
+ case GLSL_TYPE_UINT:
+ if (a->value.u[c0] < b->value.u[c1])
+ foundless = true;
+ else if (a->value.u[c0] > b->value.u[c1])
+ foundgreater = true;
+ else
+ foundequal = true;
+ break;
+ case GLSL_TYPE_INT:
+ if (a->value.i[c0] < b->value.i[c1])
+ foundless = true;
+ else if (a->value.i[c0] > b->value.i[c1])
+ foundgreater = true;
+ else
+ foundequal = true;
+ break;
+ case GLSL_TYPE_FLOAT:
+ if (a->value.f[c0] < b->value.f[c1])
+ foundless = true;
+ else if (a->value.f[c0] > b->value.f[c1])
+ foundgreater = true;
+ else
+ foundequal = true;
+ break;
+ case GLSL_TYPE_DOUBLE:
+ if (a->value.d[c0] < b->value.d[c1])
+ foundless = true;
+ else if (a->value.d[c0] > b->value.d[c1])
+ foundgreater = true;
+ else
+ foundequal = true;
+ break;
+ default:
+ unreachable("not reached");
+ }
+ }
+
+ if (foundless && foundgreater) {
+ /* Some components are strictly lower, others are strictly greater */
+ return MIXED;
+ }
+
+ if (foundequal) {
+ /* It is not mixed, but it is not strictly lower or greater */
+ if (foundless)
+ return LESS_OR_EQUAL;
+ if (foundgreater)
+ return GREATER_OR_EQUAL;
+ return EQUAL;
+ }
+
+ /* All components are strictly lower or strictly greater */
+ return foundless ? LESS : GREATER;
+}
+
+static ir_constant *
+combine_constant(bool ismin, ir_constant *a, ir_constant *b)
+{
+ void *mem_ctx = ralloc_parent(a);
+ ir_constant *c = a->clone(mem_ctx, NULL);
+ for (unsigned i = 0; i < c->type->components(); i++) {
+ switch (c->type->base_type) {
+ case GLSL_TYPE_UINT:
+ if ((ismin && b->value.u[i] < c->value.u[i]) ||
+ (!ismin && b->value.u[i] > c->value.u[i]))
+ c->value.u[i] = b->value.u[i];
+ break;
+ case GLSL_TYPE_INT:
+ if ((ismin && b->value.i[i] < c->value.i[i]) ||
+ (!ismin && b->value.i[i] > c->value.i[i]))
+ c->value.i[i] = b->value.i[i];
+ break;
+ case GLSL_TYPE_FLOAT:
+ if ((ismin && b->value.f[i] < c->value.f[i]) ||
+ (!ismin && b->value.f[i] > c->value.f[i]))
+ c->value.f[i] = b->value.f[i];
+ break;
+ case GLSL_TYPE_DOUBLE:
+ if ((ismin && b->value.d[i] < c->value.d[i]) ||
+ (!ismin && b->value.d[i] > c->value.d[i]))
+ c->value.d[i] = b->value.d[i];
+ break;
+ default:
+ assert(!"not reached");
+ }
+ }
+ return c;
+}
+
+static ir_constant *
+smaller_constant(ir_constant *a, ir_constant *b)
+{
+ assert(a != NULL);
+ assert(b != NULL);
+
+ enum compare_components_result ret = compare_components(a, b);
+ if (ret == MIXED)
+ return combine_constant(true, a, b);
+ else if (ret < EQUAL)
+ return a;
+ else
+ return b;
+}
+
+static ir_constant *
+larger_constant(ir_constant *a, ir_constant *b)
+{
+ assert(a != NULL);
+ assert(b != NULL);
+
+ enum compare_components_result ret = compare_components(a, b);
+ if (ret == MIXED)
+ return combine_constant(false, a, b);
+ else if (ret < EQUAL)
+ return b;
+ else
+ return a;
+}
+
+/* Combines two ranges by doing an element-wise min() / max() depending on the
+ * operation.
+ */
+static minmax_range
+combine_range(minmax_range r0, minmax_range r1, bool ismin)
+{
+ minmax_range ret;
+
+ if (!r0.low) {
+ ret.low = ismin ? r0.low : r1.low;
+ } else if (!r1.low) {
+ ret.low = ismin ? r1.low : r0.low;
+ } else {
+ ret.low = ismin ? smaller_constant(r0.low, r1.low) :
+ larger_constant(r0.low, r1.low);
+ }
+
+ if (!r0.high) {
+ ret.high = ismin ? r1.high : r0.high;
+ } else if (!r1.high) {
+ ret.high = ismin ? r0.high : r1.high;
+ } else {
+ ret.high = ismin ? smaller_constant(r0.high, r1.high) :
+ larger_constant(r0.high, r1.high);
+ }
+
+ return ret;
+}
+
+/* Returns a range so that lower limit is the larger of the two lower limits,
+ * and higher limit is the smaller of the two higher limits.
+ */
+static minmax_range
+range_intersection(minmax_range r0, minmax_range r1)
+{
+ minmax_range ret;
+
+ if (!r0.low)
+ ret.low = r1.low;
+ else if (!r1.low)
+ ret.low = r0.low;
+ else
+ ret.low = larger_constant(r0.low, r1.low);
+
+ if (!r0.high)
+ ret.high = r1.high;
+ else if (!r1.high)
+ ret.high = r0.high;
+ else
+ ret.high = smaller_constant(r0.high, r1.high);
+
+ return ret;
+}
+
+static minmax_range
+get_range(ir_rvalue *rval)
+{
+ ir_expression *expr = rval->as_expression();
+ if (expr && (expr->operation == ir_binop_min ||
+ expr->operation == ir_binop_max)) {
+ minmax_range r0 = get_range(expr->operands[0]);
+ minmax_range r1 = get_range(expr->operands[1]);
+ return combine_range(r0, r1, expr->operation == ir_binop_min);
+ }
+
+ ir_constant *c = rval->as_constant();
+ if (c) {
+ return minmax_range(c, c);
+ }
+
+ return minmax_range();
+}
+
+/**
+ * Prunes a min/max expression considering the base range of the parent
+ * min/max expression.
+ *
+ * @param baserange the range that the parents of this min/max expression
+ * in the min/max tree will clamp its value to.
+ */
+ir_rvalue *
+ir_minmax_visitor::prune_expression(ir_expression *expr, minmax_range baserange)
+{
+ assert(expr->operation == ir_binop_min ||
+ expr->operation == ir_binop_max);
+
+ bool ismin = expr->operation == ir_binop_min;
+ minmax_range limits[2];
+
+ /* Recurse to get the ranges for each of the subtrees of this
+ * expression. We need to do this as a separate step because we need to
+ * know the ranges of each of the subtrees before we prune either one.
+ * Consider something like this:
+ *
+ * max
+ * / \
+ * max max
+ * / \ / \
+ * 3 a b 2
+ *
+ * We would like to prune away the max on the bottom-right, but to do so
+ * we need to know the range of the expression on the left beforehand,
+ * and there's no guarantee that we will visit either subtree in a
+ * particular order.
+ */
+ for (unsigned i = 0; i < 2; ++i)
+ limits[i] = get_range(expr->operands[i]);
+
+ for (unsigned i = 0; i < 2; ++i) {
+ bool is_redundant = false;
+
+ enum compare_components_result cr = LESS;
+ if (ismin) {
+ /* If this operand will always be greater than the other one, it's
+ * redundant.
+ */
+ if (limits[i].low && limits[1 - i].high) {
+ cr = compare_components(limits[i].low, limits[1 - i].high);
+ if (cr >= EQUAL && cr != MIXED)
+ is_redundant = true;
+ }
+ /* If this operand is always greater than baserange, then even if
+ * it's smaller than the other one it'll get clamped, so it's
+ * redundant.
+ */
+ if (!is_redundant && limits[i].low && baserange.high) {
+ cr = compare_components(limits[i].low, baserange.high);
+ if (cr >= EQUAL && cr != MIXED)
+ is_redundant = true;
+ }
+ } else {
+ /* If this operand will always be lower than the other one, it's
+ * redundant.
+ */
+ if (limits[i].high && limits[1 - i].low) {
+ cr = compare_components(limits[i].high, limits[1 - i].low);
+ if (cr <= EQUAL)
+ is_redundant = true;
+ }
+ /* If this operand is always lower than baserange, then even if
+ * it's greater than the other one it'll get clamped, so it's
+ * redundant.
+ */
+ if (!is_redundant && limits[i].high && baserange.low) {
+ cr = compare_components(limits[i].high, baserange.low);
+ if (cr <= EQUAL)
+ is_redundant = true;
+ }
+ }
+
+ if (is_redundant) {
+ progress = true;
+
+ /* Recurse if necessary. */
+ ir_expression *op_expr = expr->operands[1 - i]->as_expression();
+ if (op_expr && (op_expr->operation == ir_binop_min ||
+ op_expr->operation == ir_binop_max)) {
+ return prune_expression(op_expr, baserange);
+ }
+
+ return expr->operands[1 - i];
+ } else if (cr == MIXED) {
+ /* If we have mixed vector operands, we can try to resolve the minmax
+ * expression by doing a component-wise minmax:
+ *
+ * min min
+ * / \ / \
+ * min a ===> [1,1] a
+ * / \
+ * [1,3] [3,1]
+ *
+ */
+ ir_constant *a = expr->operands[0]->as_constant();
+ ir_constant *b = expr->operands[1]->as_constant();
+ if (a && b)
+ return combine_constant(ismin, a, b);
+ }
+ }
+
+ /* Now recurse to operands giving them the proper baserange. The baserange
+ * to pass is the intersection of our baserange and the other operand's
+ * limit with one of the ranges unlimited. If we can't compute a valid
+ * intersection, we use the current baserange.
+ */
+ for (unsigned i = 0; i < 2; ++i) {
+ ir_expression *op_expr = expr->operands[i]->as_expression();
+ if (op_expr && (op_expr->operation == ir_binop_min ||
+ op_expr->operation == ir_binop_max)) {
+ /* We can only compute a new baserange for this operand if we managed
+ * to compute a valid range for the other operand.
+ */
+ if (ismin)
+ limits[1 - i].low = NULL;
+ else
+ limits[1 - i].high = NULL;
+ minmax_range base = range_intersection(limits[1 - i], baserange);
+ expr->operands[i] = prune_expression(op_expr, base);
+ }
+ }
+
+ /* If we got here we could not discard any of the operands of the minmax
+ * expression, but we can still try to resolve the expression if both
+ * operands are constant. We do this after the loop above, to make sure
+ * that if our operands are minmax expressions we have tried to prune them
+ * first (hopefully reducing them to constants).
+ */
+ ir_constant *a = expr->operands[0]->as_constant();
+ ir_constant *b = expr->operands[1]->as_constant();
+ if (a && b)
+ return combine_constant(ismin, a, b);
+
+ return expr;
+}
+
+static ir_rvalue *
+swizzle_if_required(ir_expression *expr, ir_rvalue *rval)
+{
+ if (expr->type->is_vector() && rval->type->is_scalar()) {
+ return swizzle(rval, SWIZZLE_XXXX, expr->type->vector_elements);
+ } else {
+ return rval;
+ }
+}
+
+void
+ir_minmax_visitor::handle_rvalue(ir_rvalue **rvalue)
+{
+ if (!*rvalue)
+ return;
+
+ ir_expression *expr = (*rvalue)->as_expression();
+ if (!expr || (expr->operation != ir_binop_min &&
+ expr->operation != ir_binop_max))
+ return;
+
+ ir_rvalue *new_rvalue = prune_expression(expr, minmax_range());
+ if (new_rvalue == *rvalue)
+ return;
+
+ /* If the expression type is a vector and the optimization leaves a scalar
+ * as the result, we need to turn it into a vector.
+ */
+ *rvalue = swizzle_if_required(expr, new_rvalue);
+
+ progress = true;
+}
+
+}
+
+bool
+do_minmax_prune(exec_list *instructions)
+{
+ ir_minmax_visitor v;
+
+ visit_list_elements(&v, instructions);
+
+ return v.progress;
+}
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