src/arm/jump-target-arm.cc

// Copyright 2008 the V8 project authors. All rights reserved.
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// modification, are permitted provided that the following conditions are
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//
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#include "v8.h"

#include "codegen-inl.h"
#include "jump-target-inl.h"
#include "register-allocator-inl.h"

namespace v8 {
namespace internal {

// -------------------------------------------------------------------------
// JumpTarget implementation.

#define __ ACCESS_MASM(cgen()->masm())

void JumpTarget::DoJump() {
  ASSERT(cgen()->has_valid_frame());
  // Live non-frame registers are not allowed at unconditional jumps
  // because we have no way of invalidating the corresponding results
  // which are still live in the C++ code.
  ASSERT(cgen()->HasValidEntryRegisters());

  if (is_bound()) {
    // Backward jump.  There already a frame expectation at the target.
    ASSERT(direction_ == BIDIRECTIONAL);
    cgen()->frame()->MergeTo(entry_frame_);
    cgen()->DeleteFrame();
  } else {
    // Use the current frame as the expected one at the target if necessary.
    if (entry_frame_ == NULL) {
      entry_frame_ = cgen()->frame();
      RegisterFile empty;
      cgen()->SetFrame(NULL, &empty);
    } else {
      cgen()->frame()->MergeTo(entry_frame_);
      cgen()->DeleteFrame();
    }

    // The predicate is_linked() should be made true.  Its implementation
    // detects the presence of a frame pointer in the reaching_frames_ list.
    if (!is_linked()) {
      reaching_frames_.Add(NULL);
      ASSERT(is_linked());
    }
  }
  __ jmp(&entry_label_);
}


void JumpTarget::DoBranch(Condition cc, Hint ignored) {
  ASSERT(cgen()->has_valid_frame());

  if (is_bound()) {
    ASSERT(direction_ == BIDIRECTIONAL);
    // Backward branch.  We have an expected frame to merge to on the
    // backward edge.
    cgen()->frame()->MergeTo(entry_frame_);
  } else {
    // Clone the current frame to use as the expected one at the target if
    // necessary.
    if (entry_frame_ == NULL) {
      entry_frame_ = new VirtualFrame(cgen()->frame());
    }
    // The predicate is_linked() should be made true.  Its implementation
    // detects the presence of a frame pointer in the reaching_frames_ list.
    if (!is_linked()) {
      reaching_frames_.Add(NULL);
      ASSERT(is_linked());
    }
  }
  __ b(cc, &entry_label_);
}


void JumpTarget::Call() {
  // Call is used to push the address of the catch block on the stack as
  // a return address when compiling try/catch and try/finally.  We
  // fully spill the frame before making the call.  The expected frame
  // at the label (which should be the only one) is the spilled current
  // frame plus an in-memory return address.  The "fall-through" frame
  // at the return site is the spilled current frame.
  ASSERT(cgen()->has_valid_frame());
  // There are no non-frame references across the call.
  ASSERT(cgen()->HasValidEntryRegisters());
  ASSERT(!is_linked());

  // Calls are always 'forward' so we use a copy of the current frame (plus
  // one for a return address) as the expected frame.
  ASSERT(entry_frame_ == NULL);
  VirtualFrame* target_frame = new VirtualFrame(cgen()->frame());
  target_frame->Adjust(1);
  entry_frame_ = target_frame;

  // The predicate is_linked() should now be made true.  Its implementation
  // detects the presence of a frame pointer in the reaching_frames_ list.
  reaching_frames_.Add(NULL);
  ASSERT(is_linked());

  __ bl(&entry_label_);
}


void JumpTarget::DoBind() {
  ASSERT(!is_bound());

  // Live non-frame registers are not allowed at the start of a basic
  // block.
  ASSERT(!cgen()->has_valid_frame() || cgen()->HasValidEntryRegisters());

  if (cgen()->has_valid_frame()) {
    // If there is a current frame we can use it on the fall through.
    if (entry_frame_ == NULL) {
      entry_frame_ = new VirtualFrame(cgen()->frame());
    } else {
      ASSERT(cgen()->frame()->Equals(entry_frame_));
    }
  } else {
    // If there is no current frame we must have an entry frame which we can
    // copy.
    ASSERT(entry_frame_ != NULL);
    RegisterFile empty;
    cgen()->SetFrame(new VirtualFrame(entry_frame_), &empty);
  }

  // The predicate is_linked() should be made false.  Its implementation
  // detects the presence (or absence) of frame pointers in the
  // reaching_frames_ list.  If we inserted a bogus frame to make
  // is_linked() true, remove it now.
  if (is_linked()) {
    reaching_frames_.Clear();
  }

  __ bind(&entry_label_);
}


void BreakTarget::Jump() {
  // On ARM we do not currently emit merge code for jumps, so we need to do
  // it explicitly here.  The only merging necessary is to drop extra
  // statement state from the stack.
  ASSERT(cgen()->has_valid_frame());
  int count = cgen()->frame()->height() - expected_height_;
  cgen()->frame()->Drop(count);
  DoJump();
}


void BreakTarget::Jump(Result* arg) {
  // On ARM we do not currently emit merge code for jumps, so we need to do
  // it explicitly here.  The only merging necessary is to drop extra
  // statement state from the stack.
  ASSERT(cgen()->has_valid_frame());
  int count = cgen()->frame()->height() - expected_height_;
  cgen()->frame()->Drop(count);
  cgen()->frame()->Push(arg);
  DoJump();
}


void BreakTarget::Bind() {
#ifdef DEBUG
  // All the forward-reaching frames should have been adjusted at the
  // jumps to this target.
  for (int i = 0; i < reaching_frames_.length(); i++) {
    ASSERT(reaching_frames_[i] == NULL ||
           reaching_frames_[i]->height() == expected_height_);
  }
#endif
  // Drop leftover statement state from the frame before merging, even
  // on the fall through.  This is so we can bind the return target
  // with state on the frame.
  if (cgen()->has_valid_frame()) {
    int count = cgen()->frame()->height() - expected_height_;
    // On ARM we do not currently emit merge code at binding sites, so we need
    // to do it explicitly here.  The only merging necessary is to drop extra
    // statement state from the stack.
    cgen()->frame()->Drop(count);
  }

  DoBind();
}


void BreakTarget::Bind(Result* arg) {
#ifdef DEBUG
  // All the forward-reaching frames should have been adjusted at the
  // jumps to this target.
  for (int i = 0; i < reaching_frames_.length(); i++) {
    ASSERT(reaching_frames_[i] == NULL ||
           reaching_frames_[i]->height() == expected_height_ + 1);
  }
#endif
  // Drop leftover statement state from the frame before merging, even
  // on the fall through.  This is so we can bind the return target
  // with state on the frame.
  if (cgen()->has_valid_frame()) {
    int count = cgen()->frame()->height() - expected_height_;
    // On ARM we do not currently emit merge code at binding sites, so we need
    // to do it explicitly here.  The only merging necessary is to drop extra
    // statement state from the stack.
    cgen()->frame()->ForgetElements(count);
    cgen()->frame()->Push(arg);
  }
  DoBind();
  *arg = cgen()->frame()->Pop();
}


#undef __


} }  // namespace v8::internal