factor/vm/quotations.cpp

#include "master.hpp"

namespace factor {

/* Simple non-optimizing compiler.

This is one of the two compilers implementing Factor; the second one is written
in Factor and performs advanced optimizations. See
basis/compiler/compiler.factor.

The non-optimizing compiler compiles a quotation at a time by
concatenating machine code chunks; prolog, epilog, call word, jump to
word, etc. These machine code chunks are generated from Factor code in
basis/bootstrap/assembler/.

Calls to words and constant quotations (referenced by conditionals and dips)
are direct jumps to machine code blocks. Literals are also referenced directly
without going through the literal table.

It actually does do a little bit of very simple optimization:

1) Tail call optimization.

2) If a quotation is determined to not call any other words (except for a few
special words which are open-coded, see below), then no prolog/epilog is
generated.

3) When in tail position and immediately preceded by literal arguments, the
'if' is generated inline, instead of as a call to the 'if' word.

4) When preceded by a quotation, calls to 'dip', '2dip' and '3dip' are
open-coded as retain stack manipulation surrounding a subroutine call.

5) Sub-primitives are primitive words which are implemented in assembly and not
in the VM. They are open-coded and no subroutine call is generated. This
includes stack shufflers, some fixnum arithmetic words, and words such as tag,
slot and eq?. A primitive call is relatively expensive (two subroutine calls)
so this results in a big speedup for relatively little effort. */

void quotation_jit::init_quotation(cell quot) {
  elements = untag<quotation>(quot)->array;
}

bool quotation_jit::fast_if_p(cell i, cell length) {
  return (i + 3) == length &&
      TAG(array_nth(elements.untagged(), i + 1)) == QUOTATION_TYPE &&
      array_nth(elements.untagged(), i + 2) == parent->special_objects[JIT_IF_WORD];
}

bool quotation_jit::primitive_call_p(cell i, cell length) {
  cell jit_primitive_word = parent->special_objects[JIT_PRIMITIVE_WORD];
  return (i + 2) <= length &&
      array_nth(elements.untagged(), i + 1) == jit_primitive_word;
}

bool quotation_jit::fast_dip_p(cell i, cell length) {
  cell jit_dip_word = parent->special_objects[JIT_DIP_WORD];
  return (i + 2) <= length &&
      array_nth(elements.untagged(), i + 1) == jit_dip_word;
}

bool quotation_jit::fast_2dip_p(cell i, cell length) {
  cell jit_2dip_word = parent->special_objects[JIT_2DIP_WORD];
  return (i + 2) <= length &&
      array_nth(elements.untagged(), i + 1) == jit_2dip_word;
}

bool quotation_jit::fast_3dip_p(cell i, cell length) {
  cell jit_3dip_word = parent->special_objects[JIT_3DIP_WORD];
  return (i + 2) <= length &&
      array_nth(elements.untagged(), i + 1) == jit_3dip_word;
}

bool quotation_jit::declare_p(cell i, cell length) {
  cell jit_declare_word = parent->special_objects[JIT_DECLARE_WORD];
  return (i + 2) <= length &&
      array_nth(elements.untagged(), i + 1) == jit_declare_word;
}

bool quotation_jit::mega_lookup_p(cell i, cell length) {
  return (i + 4) <= length &&
      TAG(array_nth(elements.untagged(), i + 1)) == FIXNUM_TYPE &&
      TAG(array_nth(elements.untagged(), i + 2)) == ARRAY_TYPE &&
      array_nth(elements.untagged(), i + 3) == parent->special_objects[MEGA_LOOKUP_WORD];
}

bool quotation_jit::special_subprimitive_p(cell obj) {
  // Subprimitives should be flagged with whether they require a stack frame.
  // See #295.
  return obj == parent->special_objects[SIGNAL_HANDLER_WORD] ||
         obj == parent->special_objects[LEAF_SIGNAL_HANDLER_WORD] ||
         obj == parent->special_objects[UNWIND_NATIVE_FRAMES_WORD];
}

bool quotation_jit::word_safepoint_p(cell obj) {
  return !special_subprimitive_p(obj);
}

/* true if there are no non-safepoint words in the quoation... */
bool quotation_jit::no_non_safepoint_words_p() {
  cell length = array_capacity(elements.untagged());
  for (cell i = 0; i < length; i++) {
    cell obj = array_nth(elements.untagged(), i);
    if (TAG(obj) == WORD_TYPE && !word_safepoint_p(obj))
      return false;
  }
  return true;
}

bool quotation_jit::trivial_quotation_p(array* elements) {
  return array_capacity(elements) == 1 &&
      TAG(array_nth(elements, 0)) == WORD_TYPE;
}

/* Allocates memory (emit) */
void quotation_jit::emit_epilog(bool needed) {
  if (needed) {
    emit(parent->special_objects[JIT_SAFEPOINT]);
    emit(parent->special_objects[JIT_EPILOG]);
  }
}

/* Allocates memory conditionally */
void quotation_jit::emit_quotation(cell quot_) {
  data_root<quotation> quot(quot_, parent);

  array* elements = untag<array>(quot->array);

  /* If the quotation consists of a single word, compile a direct call
     to the word. */
  if (trivial_quotation_p(elements))
    literal(array_nth(elements, 0));
  else {
    if (compiling)
      parent->jit_compile_quotation(quot.value(), relocate);
    literal(quot.value());
  }
}

/* Allocates memory (parameter(), literal(), emit_epilog, emit_with_literal)*/
void quotation_jit::iterate_quotation() {
  bool no_non_safepoint_words = no_non_safepoint_words_p();

  set_position(0);

  if (no_non_safepoint_words) {
    emit(parent->special_objects[JIT_SAFEPOINT]);
    emit(parent->special_objects[JIT_PROLOG]);
  }

  cell length = array_capacity(elements.untagged());
  bool tail_call = false;

  for (cell i = 0; i < length; i++) {
    set_position(i);

    data_root<object> obj(array_nth(elements.untagged(), i), parent);

    switch (obj.type()) {
      case WORD_TYPE:
        /* Sub-primitives */
        if (to_boolean(obj.as<word>()->subprimitive)) {
          tail_call = emit_subprimitive(obj.value(),     /* word */
                                        i == length - 1, /* tail_call_p */
                                        no_non_safepoint_words);    /* stack_frame_p */
        }                                                /* Everything else */
        else if (i == length - 1) {
          emit_epilog(no_non_safepoint_words);
          tail_call = true;
          word_jump(obj.value());
        } else
          word_call(obj.value());
        break;
      case WRAPPER_TYPE:
        push(obj.as<wrapper>()->object);
        break;
      case BYTE_ARRAY_TYPE:
        /* Primitive calls */
        if (primitive_call_p(i, length)) {
/* On x86-64 and PowerPC, the VM pointer is stored in
   a register; on other platforms, the RT_VM relocation
   is used and it needs an offset parameter */
#ifdef FACTOR_X86
          parameter(tag_fixnum(0));
#endif
          parameter(obj.value());
          parameter(false_object);
#ifdef FACTOR_PPC_TOC
          parameter(obj.value());
          parameter(false_object);
#endif
          emit(parent->special_objects[JIT_PRIMITIVE]);

          i++;
        } else
          push(obj.value());
        break;
      case QUOTATION_TYPE:
        /* 'if' preceded by two literal quotations (this is why if and ? are
           mutually recursive in the library, but both still work) */
        if (fast_if_p(i, length)) {
          emit_epilog(no_non_safepoint_words);
          tail_call = true;

          emit_quotation(array_nth(elements.untagged(), i));
          emit_quotation(array_nth(elements.untagged(), i + 1));
          emit(parent->special_objects[JIT_IF]);

          i += 2;
        } /* dip */
        else if (fast_dip_p(i, length)) {
          emit_quotation(obj.value());
          emit(parent->special_objects[JIT_DIP]);
          i++;
        } /* 2dip */
        else if (fast_2dip_p(i, length)) {
          emit_quotation(obj.value());
          emit(parent->special_objects[JIT_2DIP]);
          i++;
        } /* 3dip */
        else if (fast_3dip_p(i, length)) {
          emit_quotation(obj.value());
          emit(parent->special_objects[JIT_3DIP]);
          i++;
        } else
          push(obj.value());
        break;
      case ARRAY_TYPE:
        /* Method dispatch */
        if (mega_lookup_p(i, length)) {
          fixnum index = untag_fixnum(array_nth(elements.untagged(), i + 1));
          /* Load the object from the datastack, then remove our stack frame. */
          emit_with_literal(parent->special_objects[PIC_LOAD],
                            tag_fixnum(-index * sizeof(cell)));
          emit_epilog(no_non_safepoint_words);
          tail_call = true;

          emit_mega_cache_lookup(array_nth(elements.untagged(), i), index,
                                 array_nth(elements.untagged(), i + 2));
          i += 3;
        } /* Non-optimizing compiler ignores declarations */
        else if (declare_p(i, length))
          i++;
        else
          push(obj.value());
        break;
      default:
        push(obj.value());
        break;
    }
  }

  if (!tail_call) {
    set_position(length);
    emit_epilog(no_non_safepoint_words);
    emit(parent->special_objects[JIT_RETURN]);
  }
}

cell quotation_jit::word_stack_frame_size(cell obj) {
  if (special_subprimitive_p(obj))
    return SIGNAL_HANDLER_STACK_FRAME_SIZE;
  return JIT_FRAME_SIZE;
}

/* Allocates memory */
code_block* factor_vm::jit_compile_quotation(cell owner_, cell quot_,
                                             bool relocating) {
  data_root<object> owner(owner_, this);
  data_root<quotation> quot(quot_, this);

  quotation_jit compiler(owner.value(), true, relocating, this);
  compiler.init_quotation(quot.value());
  compiler.iterate_quotation();

  cell frame_size = compiler.word_stack_frame_size(owner_);

  code_block* compiled = compiler.to_code_block(frame_size);

  if (relocating)
    initialize_code_block(compiled);

  return compiled;
}

/* Allocates memory */
void factor_vm::jit_compile_quotation(cell quot_, bool relocating) {
  data_root<quotation> quot(quot_, this);
  if (!quotation_compiled_p(quot.untagged())) {
    code_block* compiled =
        jit_compile_quotation(quot.value(), quot.value(), relocating);
    quot.untagged()->entry_point = compiled->entry_point();
  }
}

/* Allocates memory */
void factor_vm::primitive_jit_compile() {
  jit_compile_quotation(ctx->pop(), true);
}

cell factor_vm::lazy_jit_compile_entry_point() {
  return untag<word>(special_objects[LAZY_JIT_COMPILE_WORD])->entry_point;
}

/* push a new quotation on the stack */
/* Allocates memory */
void factor_vm::primitive_array_to_quotation() {
  quotation* quot = allot<quotation>(sizeof(quotation));

  quot->array = ctx->peek();
  quot->cached_effect = false_object;
  quot->cache_counter = false_object;
  quot->entry_point = lazy_jit_compile_entry_point();

  ctx->replace(tag<quotation>(quot));
}

/* Allocates memory (from_unsigned_cell) */
void factor_vm::primitive_quotation_code() {
  data_root<quotation> quot(ctx->pop(), this);

  ctx->push(from_unsigned_cell(quot->entry_point));
  ctx->push(from_unsigned_cell((cell)quot->code() + quot->code()->size()));
}

/* Allocates memory */
fixnum factor_vm::quot_code_offset_to_scan(cell quot_, cell offset) {
  data_root<quotation> quot(quot_, this);
  data_root<array> array(quot->array, this);

  quotation_jit compiler(quot.value(), false, false, this);
  compiler.init_quotation(quot.value());
  compiler.compute_position(offset);
  compiler.iterate_quotation();

  return compiler.get_position();
}

/* Allocates memory */
cell factor_vm::lazy_jit_compile(cell quot_) {
  data_root<quotation> quot(quot_, this);

  FACTOR_ASSERT(!quotation_compiled_p(quot.untagged()));

  code_block* compiled =
      jit_compile_quotation(quot.value(), quot.value(), true);
  quot.untagged()->entry_point = compiled->entry_point();

  return quot.value();
}

/* Allocates memory */
VM_C_API cell lazy_jit_compile(cell quot, factor_vm* parent) {
  return parent->lazy_jit_compile(quot);
}

bool factor_vm::quotation_compiled_p(quotation* quot) {
  return quot->entry_point != 0 &&
         quot->entry_point != lazy_jit_compile_entry_point();
}

void factor_vm::primitive_quotation_compiled_p() {
  quotation* quot = untag_check<quotation>(ctx->pop());
  ctx->push(tag_boolean(quotation_compiled_p(quot)));
}

}