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/*
* Copyright (C) 2019 Alyssa Rosenzweig <alyssa@rosenzweig.io>
* Copyright (C) 2019 Collabora, Ltd.
*
* 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.
*/
#include "compiler.h"
/* Creates pipeline registers. This is a prepass run before the main register
* allocator but after scheduling, once bundles are created. It works by
* iterating the scheduled IR, checking if a value is ever used after the end
* of the current bundle. If it is not, it is promoted to a bundle-specific
* pipeline register.
*
* Pipeline registers are only written from the first two stages of the
* pipeline (vmul/sadd) lasting the duration of the bundle only. There are two
* 128-bit pipeline registers available (r24/r25). The upshot is that no actual
* register allocation is needed; we can _always_ promote a value to a pipeline
* register, liveness permitting. This greatly simplifies the logic of this
* passing, negating the need for a proper RA like work registers.
*/
static bool
mir_pipeline_ins(
compiler_context *ctx,
midgard_block *block,
midgard_bundle *bundle, unsigned i,
unsigned pipeline_count)
{
midgard_instruction *ins = bundle->instructions[i];
/* We could be pipelining a register, so we need to make sure that all
* of the components read in this bundle are written in this bundle,
* and that no components are written before this bundle */
unsigned node = ins->dest;
unsigned read_mask = 0;
/* Analyze the bundle for a per-byte read mask */
for (unsigned j = 0; j < bundle->instruction_count; ++j) {
midgard_instruction *q = bundle->instructions[j];
read_mask |= mir_bytemask_of_read_components(q, node);
/* The fragment colour can't be pipelined (well, it is
* pipelined in r0, but this is a delicate dance with
* scheduling and RA, not for us to worry about) */
if (q->compact_branch && q->writeout && mir_has_arg(q, node))
return false;
}
/* Now analyze for a write mask */
for (unsigned j = 0; j < bundle->instruction_count; ++j) {
midgard_instruction *q = bundle->instructions[j];
if (q->dest != node) continue;
/* Remove the written mask from the read requirements */
read_mask &= ~mir_bytemask(q);
}
/* Check for leftovers */
if (read_mask)
return false;
/* Now, check outside the bundle */
midgard_instruction *start = bundle->instructions[0];
if (mir_is_written_before(ctx, start, node))
return false;
/* We want to know if we live after this bundle, so check if
* we're live after the last instruction of the bundle */
midgard_instruction *end = bundle->instructions[
bundle->instruction_count - 1];
if (mir_is_live_after(ctx, block, end, ins->dest))
return false;
/* We're only live in this bundle -- pipeline! */
mir_rewrite_index(ctx, node, SSA_FIXED_REGISTER(24 + pipeline_count));
return true;
}
void
mir_create_pipeline_registers(compiler_context *ctx)
{
mir_invalidate_liveness(ctx);
mir_foreach_block(ctx, block) {
mir_foreach_bundle_in_block(block, bundle) {
if (!mir_is_alu_bundle(bundle)) continue;
if (bundle->instruction_count < 2) continue;
/* Only first 2 instructions could pipeline */
bool succ = mir_pipeline_ins(ctx, block, bundle, 0, 0);
mir_pipeline_ins(ctx, block, bundle, 1, succ);
}
}
}
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