src/arm/jump-target-arm.cc

// Copyright 2008 the V8 project authors. All rights reserved.
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#include "v8.h"

#if defined(V8_TARGET_ARCH_ARM)

#include "codegen-inl.h"
#include "jump-target-inl.h"
#include "register-allocator-inl.h"
#include "virtual-frame-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 (entry_frame_set_) {
    if (entry_label_.is_bound()) {
      // If we already bound and generated code at the destination then it
      // is too late to ask for less optimistic type assumptions.
      ASSERT(entry_frame_.IsCompatibleWith(cgen()->frame()));
    }
    // There already a frame expectation at the target.
    cgen()->frame()->MergeTo(&entry_frame_);
    cgen()->DeleteFrame();
  } else {
    // Clone the current frame to use as the expected one at the target.
    set_entry_frame(cgen()->frame());
    // Zap the fall-through frame since the jump was unconditional.
    RegisterFile empty;
    cgen()->SetFrame(NULL, &empty);
  }
  if (entry_label_.is_bound()) {
    // You can't jump backwards to an already bound label unless you admitted
    // up front that this was a bidirectional jump target.  Bidirectional jump
    // targets will zap their type info when bound in case some later virtual
    // frame with less precise type info branches to them.
    ASSERT(direction_ != FORWARD_ONLY);
  }
  __ jmp(&entry_label_);
}


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

  if (entry_frame_set_) {
    if (entry_label_.is_bound()) {
      // If we already bound and generated code at the destination then it
      // is too late to ask for less optimistic type assumptions.
      ASSERT(entry_frame_.IsCompatibleWith(cgen()->frame()));
    }
    // We have an expected frame to merge to on the backward edge.
    cgen()->frame()->MergeTo(&entry_frame_, cond);
  } else {
    // Clone the current frame to use as the expected one at the target.
    set_entry_frame(cgen()->frame());
  }
  if (entry_label_.is_bound()) {
    // You can't branch backwards to an already bound label unless you admitted
    // up front that this was a bidirectional jump target.  Bidirectional jump
    // targets will zap their type info when bound in case some later virtual
    // frame with less precise type info branches to them.
    ASSERT(direction_ != FORWARD_ONLY);
  }
  __ b(cond, &entry_label_);
  if (cond == al) {
    cgen()->DeleteFrame();
  }
}


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_set_);
  VirtualFrame target_frame = *cgen()->frame();
  target_frame.Adjust(1);
  set_entry_frame(&target_frame);

  __ 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 (direction_ != FORWARD_ONLY) cgen()->frame()->ForgetTypeInfo();
    // If there is a current frame we can use it on the fall through.
    if (!entry_frame_set_) {
      entry_frame_ = *cgen()->frame();
      entry_frame_set_ = true;
    } else {
      cgen()->frame()->MergeTo(&entry_frame_);
      // On fall through we may have to merge both ways.
      if (direction_ != FORWARD_ONLY) {
        // This will not need to adjust the virtual frame entries that are
        // register allocated since that was done above and they now match.
        // But it does need to adjust the entry_frame_ of this jump target
        // to make it potentially less optimistic.  Later code can branch back
        // to this jump target and we need to assert that that code does not
        // have weaker assumptions about types.
        entry_frame_.MergeTo(cgen()->frame());
      }
    }
  } else {
    // If there is no current frame we must have an entry frame which we can
    // copy.
    ASSERT(entry_frame_set_);
    RegisterFile empty;
    cgen()->SetFrame(new VirtualFrame(&entry_frame_), &empty);
  }

  __ bind(&entry_label_);
}


#undef __


} }  // namespace v8::internal

#endif  // V8_TARGET_ARCH_ARM