[Mesa-dev] [PATCH v3] glsl: Optimize min/max expression trees
Connor Abbott
cwabbott0 at gmail.com
Mon Sep 29 10:19:14 PDT 2014
On Mon, Sep 29, 2014 at 7:49 AM, Iago Toral Quiroga <itoral at igalia.com> wrote:
> Original patch by Petri Latvala <petri.latvala at intel.com>:
>
> Add an optimization pass that drops min/max expression operands that
> can be proven to not contribute to the final result. The algorithm is
> similar to alpha-beta pruning on a minmax search, from the field of
> AI.
>
> This optimization pass can optimize min/max expressions where operands
> are min/max expressions. Such code can appear in shaders by itself, or
> as the result of clamp() or AMD_shader_trinary_minmax functions.
>
> This optimization pass improves the generated code for piglit's
> AMD_shader_trinary_minmax tests as follows:
>
> total instructions in shared programs: 75 -> 67 (-10.67%)
> instructions in affected programs: 60 -> 52 (-13.33%)
> GAINED: 0
> LOST: 0
>
> All tests (max3, min3, mid3) improved.
>
> A full shader-db run:
>
> total instructions in shared programs: 4293603 -> 4293575 (-0.00%)
> instructions in affected programs: 1188 -> 1160 (-2.36%)
> GAINED: 0
> LOST: 0
>
> Improvements happen in Guacamelee and Serious Sam 3. One shader from
> Dungeon Defenders is hurt by shader-db metrics (26 -> 28), because of
> dropping of a (constant float (0.00000)) operand, which was
> compiled to a saturate modifier.
>
> Version 2 by Iago Toral Quiroga <itoral at igalia.com>:
>
> Changes from review feedback:
> - Squashed various cosmetic changes sent by Matt Turner.
> - Make less_all_components return an enum rather than setting a class member.
> (Suggested by Mat Turner). Also, renamed it to compare_components.
> - Make less_all_components, smaller_constant and larger_constant static.
> (Suggested by Mat Turner)
> - Change mixmax_range to call its limits "low" and "high" instead of
> "range[0]" and "range[1]". (Suggested by Connor Abbot).
> - Use ir_builder swizzle helpers in swizzle_if_required(). (Suggested by
> Connor Abbot).
> - Make the logic more clearer by rearrenging the code and commenting.
> (Suggested by Connor Abbot).
> - Added comment to explain why we need to recurse twice. (Suggested by
> Connor Abbot).
> - If we cannot prune an expression, do not return early. Instead, attempt
> to prune its children. (Suggested by Connor Abbot).
>
> Other changes:
> - Instead of having a global "valid" visitor member, let the various functions
> that can determine this status return a boolean and check for its value
> to decide what to do in each case. This is more flexible and allows to
> recurse into children of parents that could not be prunned due to invalid
> ranges (so related to the last bullet in the review feedback).
> - Make sure we always check if a range is valid before working with it. Since
> any use of get_range, combine_range or range_intersection can invalidate
> a range we should check for this situation every time we use any of these
> functions.
>
> Version 3 by Iago Toral Quiroga <itoral at igalia.com>:
>
> Changes from review feedback:
> - Now we can make get_range, combine_range and range_intersection static too
> (suggested by Connor Abbot).
> - Do not return NULL when looking for the larger or greater constant into
> mixed vector constants. Instead, produce a new constant by doing a
> component-wise minmax. With this we can also remove of the validations when
> we call into these functions (suggested by Connor Abbot).
> - Add a comment explaining the meaning of the baserange argument in
> prune_expression (suggested by Connor Abbot).
>
> Other changes:
> - Eliminate minmax expressions operating on constant vectors with mixed values
> by resolving them.
>
> No piglit regressions observed with Version 3.
>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=76861
> ---
>
> Version 3 passes all minmax unit tests sent in the original series by Petri,
> except for the ones aimed at mixed vectors because this version produces
> better code for these than what is expected by these tests.
Thanks for cleaning this up! This patch is
Reviewed-by: Connor Abbott <cwabbott0 at gmail.com>
Dylan had some style comments on the Python patches IIRC, but other
than that I think they looked good (assuming you fix the broken tests
you mentioned) - it has been a while though.
>
> src/glsl/Makefile.sources | 1 +
> src/glsl/glsl_parser_extras.cpp | 1 +
> src/glsl/ir_optimization.h | 1 +
> src/glsl/opt_minmax.cpp | 464 ++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 467 insertions(+)
> create mode 100644 src/glsl/opt_minmax.cpp
>
> diff --git a/src/glsl/Makefile.sources b/src/glsl/Makefile.sources
> index cb8d5a6..1c08697 100644
> --- a/src/glsl/Makefile.sources
> +++ b/src/glsl/Makefile.sources
> @@ -95,6 +95,7 @@ LIBGLSL_FILES = \
> $(GLSL_SRCDIR)/opt_flip_matrices.cpp \
> $(GLSL_SRCDIR)/opt_function_inlining.cpp \
> $(GLSL_SRCDIR)/opt_if_simplification.cpp \
> + $(GLSL_SRCDIR)/opt_minmax.cpp \
> $(GLSL_SRCDIR)/opt_noop_swizzle.cpp \
> $(GLSL_SRCDIR)/opt_rebalance_tree.cpp \
> $(GLSL_SRCDIR)/opt_redundant_jumps.cpp \
> diff --git a/src/glsl/glsl_parser_extras.cpp b/src/glsl/glsl_parser_extras.cpp
> index 490c3c8..ae19ce4 100644
> --- a/src/glsl/glsl_parser_extras.cpp
> +++ b/src/glsl/glsl_parser_extras.cpp
> @@ -1586,6 +1586,7 @@ do_common_optimization(exec_list *ir, bool linked,
> else
> progress = do_constant_variable_unlinked(ir) || progress;
> progress = do_constant_folding(ir) || progress;
> + progress = do_minmax_prune(ir) || progress;
> progress = do_cse(ir) || progress;
> progress = do_rebalance_tree(ir) || progress;
> progress = do_algebraic(ir, native_integers, options) || progress;
> diff --git a/src/glsl/ir_optimization.h b/src/glsl/ir_optimization.h
> index 369dcd1..8fbd992 100644
> --- a/src/glsl/ir_optimization.h
> +++ b/src/glsl/ir_optimization.h
> @@ -99,6 +99,7 @@ bool opt_flatten_nested_if_blocks(exec_list *instructions);
> bool do_discard_simplification(exec_list *instructions);
> bool lower_if_to_cond_assign(exec_list *instructions, unsigned max_depth = 0);
> bool do_mat_op_to_vec(exec_list *instructions);
> +bool do_minmax_prune(exec_list *instructions);
> bool do_noop_swizzle(exec_list *instructions);
> bool do_structure_splitting(exec_list *instructions);
> bool do_swizzle_swizzle(exec_list *instructions);
> diff --git a/src/glsl/opt_minmax.cpp b/src/glsl/opt_minmax.cpp
> new file mode 100644
> index 0000000..a4fe2bd
> --- /dev/null
> +++ b/src/glsl/opt_minmax.cpp
> @@ -0,0 +1,464 @@
> +/*
> + * 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 "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;
> + 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;
> + 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);
> + }
> + }
> +
> + 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;
> +}
> --
> 1.9.1
>
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