Xenia-Canary/src/xenia/cpu/compiler/passes/simplification_pass.cc

/**
 ******************************************************************************
 * Xenia : Xbox 360 Emulator Research Project                                 *
 ******************************************************************************
 * Copyright 2013 Ben Vanik. All rights reserved.                             *
 * Released under the BSD license - see LICENSE in the root for more details. *
 ******************************************************************************
 */

#include "xenia/cpu/compiler/passes/simplification_pass.h"

#include "xenia/base/profiling.h"

namespace xe {
namespace cpu {
namespace compiler {
namespace passes {

// TODO(benvanik): remove when enums redefined.
using namespace xe::cpu::hir;

using xe::cpu::hir::HIRBuilder;
using xe::cpu::hir::Instr;
using xe::cpu::hir::Value;

SimplificationPass::SimplificationPass() : ConditionalGroupSubpass() {}

SimplificationPass::~SimplificationPass() {}

bool SimplificationPass::Run(HIRBuilder* builder, bool& result) {
  result = false;
  result |= EliminateConversions(builder);
  result |= SimplifyAssignments(builder);
  return true;
}

bool SimplificationPass::EliminateConversions(HIRBuilder* builder) {
  // First, we check for truncates/extensions that can be skipped.
  // This generates some assignments which then the second step will clean up.
  // Both zero/sign extends can be skipped:
  //   v1.i64 = zero/sign_extend v0.i32
  //   v2.i32 = truncate v1.i64
  // becomes:
  //   v1.i64 = zero/sign_extend v0.i32 (may be dead code removed later)
  //   v2.i32 = v0.i32

  bool result = false;
  auto block = builder->first_block();
  while (block) {
    auto i = block->instr_head;
    while (i) {
      // To make things easier we check in reverse (source of truncate/extend
      // back to definition).
      if (i->opcode == &OPCODE_TRUNCATE_info) {
        // Matches zero/sign_extend + truncate.
        result |= CheckTruncate(i);
      } else if (i->opcode == &OPCODE_BYTE_SWAP_info) {
        // Matches byte swap + byte swap.
        // This is pretty rare within the same basic block, but is in the
        // memcpy hot path and (probably) worth it. Maybe.
        result |= CheckByteSwap(i);
      }
      i = i->next;
    }
    block = block->next;
  }
  return result;
}

bool SimplificationPass::CheckTruncate(Instr* i) {
  // Walk backward up src's chain looking for an extend. We may have
  // assigns, so skip those.
  auto src = i->src1.value;
  auto def = src->def;
  while (def && def->opcode == &OPCODE_ASSIGN_info) {
    // Skip asignments.
    def = def->src1.value->def;
  }
  if (def) {
    if (def->opcode == &OPCODE_SIGN_EXTEND_info) {
      // Value comes from a sign extend.
      if (def->src1.value->type == i->dest->type) {
        // Types match, use original by turning this into an assign.
        i->Replace(&OPCODE_ASSIGN_info, 0);
        i->set_src1(def->src1.value);
        return true;
      }
    } else if (def->opcode == &OPCODE_ZERO_EXTEND_info) {
      // Value comes from a zero extend.
      if (def->src1.value->type == i->dest->type) {
        // Types match, use original by turning this into an assign.
        i->Replace(&OPCODE_ASSIGN_info, 0);
        i->set_src1(def->src1.value);
        return true;
      }
    }
  }
  return false;
}

bool SimplificationPass::CheckByteSwap(Instr* i) {
  // Walk backward up src's chain looking for a byte swap. We may have
  // assigns, so skip those.
  auto src = i->src1.value;
  auto def = src->def;
  while (def && def->opcode == &OPCODE_ASSIGN_info) {
    // Skip asignments.
    def = def->src1.value->def;
  }
  if (def && def->opcode == &OPCODE_BYTE_SWAP_info) {
    // Value comes from a byte swap.
    if (def->src1.value->type == i->dest->type) {
      // Types match, use original by turning this into an assign.
      i->Replace(&OPCODE_ASSIGN_info, 0);
      i->set_src1(def->src1.value);
      return true;
    }
  }
  return false;
}

bool SimplificationPass::SimplifyAssignments(HIRBuilder* builder) {
  // Run over the instructions and rename assigned variables:
  //   v1 = v0
  //   v2 = v1
  //   v3 = add v0, v2
  // becomes:
  //   v1 = v0
  //   v2 = v0
  //   v3 = add v0, v0
  // This could be run several times, as it could make other passes faster
  // to compute (for example, ConstantPropagation). DCE will take care of
  // the useless assigns.
  //
  // We do this by walking each instruction. For each value op we
  // look at its def instr to see if it's an assign - if so, we use the src
  // of that instr. Because we may have chains, we do this recursively until
  // we find a non-assign def.

  bool result = false;
  auto block = builder->first_block();
  while (block) {
    auto i = block->instr_head;
    while (i) {
      uint32_t signature = i->opcode->signature;
      if (GET_OPCODE_SIG_TYPE_SRC1(signature) == OPCODE_SIG_TYPE_V) {
        bool modified = false;
        i->set_src1(CheckValue(i->src1.value, modified));
        result |= modified;
      }
      if (GET_OPCODE_SIG_TYPE_SRC2(signature) == OPCODE_SIG_TYPE_V) {
        bool modified = false;
        i->set_src2(CheckValue(i->src2.value, modified));
        result |= modified;
      }
      if (GET_OPCODE_SIG_TYPE_SRC3(signature) == OPCODE_SIG_TYPE_V) {
        bool modified = false;
        i->set_src3(CheckValue(i->src3.value, modified));
        result |= modified;
      }
      i = i->next;
    }
    block = block->next;
  }
  return result;
}

Value* SimplificationPass::CheckValue(Value* value, bool& result) {
  auto def = value->def;
  if (def && def->opcode == &OPCODE_ASSIGN_info) {
    // Value comes from an assignment - recursively find if it comes from
    // another assignment. It probably doesn't, if we already replaced it.
    auto replacement = def->src1.value;
    while (true) {
      def = replacement->def;
      if (!def || def->opcode != &OPCODE_ASSIGN_info) {
        break;
      }
      replacement = def->src1.value;
    }
    result = true;
    return replacement;
  }
  result = false;
  return value;
}

}  // namespace passes
}  // namespace compiler
}  // namespace cpu
}  // namespace xe