/*
 * Copyright 2023 Valve Corporation
 * SPDX-License-Identifier: MIT
 */

#include "util/list.h"
#include "agx_builder.h"
#include "agx_compiler.h"

/*
 * Replaces conditional breaks:
 *
 *    if_cmp x, y, n=1 {
 *       break #value
 *    }
 *    pop_exec n=1
 *
 * with break_if_*cmp pseudo-instructions for further optimization. This
 * assumes agx_opt_empty_else has already run.
 */

static void
match_block(agx_context *ctx, agx_block *block)
{
   agx_instr *if_ = agx_last_instr(block);
   if (!if_ ||
       (if_->op != AGX_OPCODE_IF_ICMP && if_->op != AGX_OPCODE_IF_FCMP) ||
       if_->nest != 1)
      return;

   /* If's fallthrough to the then */
   agx_block *then_block = agx_next_block(block);
   assert(block->successors[0] == then_block && "successors for if");

   /* We're searching for a single block then, so the next block is else */
   agx_block *else_block = agx_next_block(then_block);
   if (block->successors[1] != else_block)
      return;

   if (!list_is_singular(&then_block->instructions) ||
       !list_is_singular(&else_block->instructions))
      return;

   agx_instr *break_ = agx_last_instr(then_block);
   agx_instr *pop = agx_last_instr(else_block);

   if (break_->op != AGX_OPCODE_BREAK || pop->op != AGX_OPCODE_POP_EXEC ||
       pop->nest != 1)
      return;

   /* Find the successor of the if */
   agx_block *after = else_block->successors[0];
   assert(else_block->successors[1] == NULL && "single successor");

   /* We are dropping one level of nesting (the if) when rewriting */
   assert(break_->nest >= 1 && "must at least break out of the if");
   unsigned new_nest = break_->nest - 1;

   /* Rewrite */
   agx_builder b = agx_init_builder(ctx, agx_before_block(after));

   if (if_->op == AGX_OPCODE_IF_FCMP) {
      agx_break_if_fcmp(&b, if_->src[0], if_->src[1], new_nest,
                        if_->invert_cond, if_->fcond, break_->target);
   } else {
      agx_break_if_icmp(&b, if_->src[0], if_->src[1], new_nest,
                        if_->invert_cond, if_->icond, break_->target);
   }

   agx_remove_instruction(if_);
   agx_remove_instruction(break_);
   agx_remove_instruction(pop);
}

void
agx_opt_break_if(agx_context *ctx)
{
   agx_foreach_block(ctx, block) {
      match_block(ctx, block);
   }
}