src/v8/src/arm64/deoptimizer-arm64.cc

// Copyright 2013 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "src/api.h"
#include "src/arm64/assembler-arm64-inl.h"
#include "src/arm64/macro-assembler-arm64-inl.h"
#include "src/deoptimizer.h"
#include "src/frame-constants.h"
#include "src/register-configuration.h"
#include "src/safepoint-table.h"


namespace v8 {
namespace internal {

#define __ masm()->

namespace {

void CopyRegListToFrame(MacroAssembler* masm, const Register& dst,
                        int dst_offset, const CPURegList& reg_list,
                        const Register& temp0, const Register& temp1,
                        int src_offset = 0) {
  DCHECK_EQ(reg_list.Count() % 2, 0);
  UseScratchRegisterScope temps(masm);
  CPURegList copy_to_input = reg_list;
  int reg_size = reg_list.RegisterSizeInBytes();
  DCHECK_EQ(temp0.SizeInBytes(), reg_size);
  DCHECK_EQ(temp1.SizeInBytes(), reg_size);

  // Compute some temporary addresses to avoid having the macro assembler set
  // up a temp with an offset for accesses out of the range of the addressing
  // mode.
  Register src = temps.AcquireX();
  masm->Add(src, masm->StackPointer(), src_offset);
  masm->Add(dst, dst, dst_offset);

  // Write reg_list into the frame pointed to by dst.
  for (int i = 0; i < reg_list.Count(); i += 2) {
    masm->Ldp(temp0, temp1, MemOperand(src, i * reg_size));

    CPURegister reg0 = copy_to_input.PopLowestIndex();
    CPURegister reg1 = copy_to_input.PopLowestIndex();
    int offset0 = reg0.code() * reg_size;
    int offset1 = reg1.code() * reg_size;

    // Pair up adjacent stores, otherwise write them separately.
    if (offset1 == offset0 + reg_size) {
      masm->Stp(temp0, temp1, MemOperand(dst, offset0));
    } else {
      masm->Str(temp0, MemOperand(dst, offset0));
      masm->Str(temp1, MemOperand(dst, offset1));
    }
  }
  masm->Sub(dst, dst, dst_offset);
}

void RestoreRegList(MacroAssembler* masm, const CPURegList& reg_list,
                    const Register& src_base, int src_offset) {
  DCHECK_EQ(reg_list.Count() % 2, 0);
  UseScratchRegisterScope temps(masm);
  CPURegList restore_list = reg_list;
  int reg_size = restore_list.RegisterSizeInBytes();

  // Compute a temporary addresses to avoid having the macro assembler set
  // up a temp with an offset for accesses out of the range of the addressing
  // mode.
  Register src = temps.AcquireX();
  masm->Add(src, src_base, src_offset);

  // Restore every register in restore_list from src.
  while (!restore_list.IsEmpty()) {
    CPURegister reg0 = restore_list.PopLowestIndex();
    CPURegister reg1 = restore_list.PopLowestIndex();
    int offset0 = reg0.code() * reg_size;
    int offset1 = reg1.code() * reg_size;

    // Pair up adjacent loads, otherwise read them separately.
    if (offset1 == offset0 + reg_size) {
      masm->Ldp(reg0, reg1, MemOperand(src, offset0));
    } else {
      masm->Ldr(reg0, MemOperand(src, offset0));
      masm->Ldr(reg1, MemOperand(src, offset1));
    }
  }
}
}  // namespace

void Deoptimizer::TableEntryGenerator::Generate() {
  GeneratePrologue();

  // TODO(all): This code needs to be revisited. We probably only need to save
  // caller-saved registers here. Callee-saved registers can be stored directly
  // in the input frame.

  // Save all allocatable double registers.
  CPURegList saved_double_registers(
      CPURegister::kVRegister, kDRegSizeInBits,
      RegisterConfiguration::Default()->allocatable_double_codes_mask());
  DCHECK_EQ(saved_double_registers.Count() % 2, 0);
  __ PushCPURegList(saved_double_registers);

  CPURegList saved_float_registers(
      CPURegister::kVRegister, kSRegSizeInBits,
      RegisterConfiguration::Default()->allocatable_float_codes_mask());
  DCHECK_EQ(saved_float_registers.Count() % 4, 0);
  __ PushCPURegList(saved_float_registers);

  // We save all the registers except sp, lr and the masm scratches.
  CPURegList saved_registers(CPURegister::kRegister, kXRegSizeInBits, 0, 28);
  saved_registers.Remove(ip0);
  saved_registers.Remove(ip1);
  saved_registers.Combine(fp);
  DCHECK_EQ(saved_registers.Count() % 2, 0);
  __ PushCPURegList(saved_registers);

  __ Mov(x3, Operand(ExternalReference(IsolateAddressId::kCEntryFPAddress,
                                       isolate())));
  __ Str(fp, MemOperand(x3));

  const int kSavedRegistersAreaSize =
      (saved_registers.Count() * kXRegSize) +
      (saved_double_registers.Count() * kDRegSize) +
      (saved_float_registers.Count() * kSRegSize);

  // Floating point registers are saved on the stack above core registers.
  const int kFloatRegistersOffset = saved_registers.Count() * kXRegSize;
  const int kDoubleRegistersOffset =
      kFloatRegistersOffset + saved_float_registers.Count() * kSRegSize;

  // Get the bailout id from the stack.
  Register bailout_id = x2;
  __ Peek(bailout_id, kSavedRegistersAreaSize);

  Register code_object = x3;
  Register fp_to_sp = x4;
  // Get the address of the location in the code object. This is the return
  // address for lazy deoptimization.
  __ Mov(code_object, lr);
  // Compute the fp-to-sp delta, adding two words for alignment padding and
  // bailout id.
  __ Add(fp_to_sp, __ StackPointer(),
         kSavedRegistersAreaSize + (2 * kPointerSize));
  __ Sub(fp_to_sp, fp, fp_to_sp);

  // Allocate a new deoptimizer object.
  __ Ldr(x1, MemOperand(fp, CommonFrameConstants::kContextOrFrameTypeOffset));

  // Ensure we can safely load from below fp.
  DCHECK_GT(kSavedRegistersAreaSize,
            -JavaScriptFrameConstants::kFunctionOffset);
  __ Ldr(x0, MemOperand(fp, JavaScriptFrameConstants::kFunctionOffset));

  // If x1 is a smi, zero x0.
  __ Tst(x1, kSmiTagMask);
  __ CzeroX(x0, eq);

  __ Mov(x1, type());
  // Following arguments are already loaded:
  //  - x2: bailout id
  //  - x3: code object address
  //  - x4: fp-to-sp delta
  __ Mov(x5, ExternalReference::isolate_address(isolate()));

  {
    // Call Deoptimizer::New().
    AllowExternalCallThatCantCauseGC scope(masm());
    __ CallCFunction(ExternalReference::new_deoptimizer_function(isolate()), 6);
  }

  // Preserve "deoptimizer" object in register x0.
  Register deoptimizer = x0;

  // Get the input frame descriptor pointer.
  __ Ldr(x1, MemOperand(deoptimizer, Deoptimizer::input_offset()));

  // Copy core registers into the input frame.
  CopyRegListToFrame(masm(), x1, FrameDescription::registers_offset(),
                     saved_registers, x2, x3);

  // Copy double registers to the input frame.
  CopyRegListToFrame(masm(), x1, FrameDescription::double_registers_offset(),
                     saved_double_registers, x2, x3, kDoubleRegistersOffset);

  // Copy float registers to the input frame.
  // TODO(arm): these are the lower 32-bits of the double registers stored
  // above, so we shouldn't need to store them again.
  CopyRegListToFrame(masm(), x1, FrameDescription::float_registers_offset(),
                     saved_float_registers, w2, w3, kFloatRegistersOffset);

  // Remove the padding, bailout id and the saved registers from the stack.
  DCHECK_EQ(kSavedRegistersAreaSize % kXRegSize, 0);
  __ Drop(2 + (kSavedRegistersAreaSize / kXRegSize));

  // Compute a pointer to the unwinding limit in register x2; that is
  // the first stack slot not part of the input frame.
  Register unwind_limit = x2;
  __ Ldr(unwind_limit, MemOperand(x1, FrameDescription::frame_size_offset()));

  // Unwind the stack down to - but not including - the unwinding
  // limit and copy the contents of the activation frame to the input
  // frame description.
  __ Add(x3, x1, FrameDescription::frame_content_offset());
  __ SlotAddress(x1, 0);
  __ Lsr(unwind_limit, unwind_limit, kPointerSizeLog2);
  __ Mov(x5, unwind_limit);
  __ CopyDoubleWords(x3, x1, x5);
  __ Drop(unwind_limit);

  // Compute the output frame in the deoptimizer.
  __ Push(padreg, x0);  // Preserve deoptimizer object across call.
  {
    // Call Deoptimizer::ComputeOutputFrames().
    AllowExternalCallThatCantCauseGC scope(masm());
    __ CallCFunction(
        ExternalReference::compute_output_frames_function(isolate()), 1);
  }
  __ Pop(x4, padreg);  // Restore deoptimizer object (class Deoptimizer).

  {
    UseScratchRegisterScope temps(masm());
    Register scratch = temps.AcquireX();
    __ Ldr(scratch, MemOperand(x4, Deoptimizer::caller_frame_top_offset()));
    __ Mov(__ StackPointer(), scratch);
  }

  // Replace the current (input) frame with the output frames.
  Label outer_push_loop, inner_push_loop,
      outer_loop_header, inner_loop_header;
  __ Ldrsw(x1, MemOperand(x4, Deoptimizer::output_count_offset()));
  __ Ldr(x0, MemOperand(x4, Deoptimizer::output_offset()));
  __ Add(x1, x0, Operand(x1, LSL, kPointerSizeLog2));
  __ B(&outer_loop_header);

  __ Bind(&outer_push_loop);
  Register current_frame = x2;
  Register frame_size = x3;
  __ Ldr(current_frame, MemOperand(x0, kPointerSize, PostIndex));
  __ Ldr(x3, MemOperand(current_frame, FrameDescription::frame_size_offset()));
  __ Lsr(frame_size, x3, kPointerSizeLog2);
  __ Claim(frame_size);

  __ Add(x7, current_frame, FrameDescription::frame_content_offset());
  __ SlotAddress(x6, 0);
  __ CopyDoubleWords(x6, x7, frame_size);

  __ Bind(&outer_loop_header);
  __ Cmp(x0, x1);
  __ B(lt, &outer_push_loop);

  __ Ldr(x1, MemOperand(x4, Deoptimizer::input_offset()));
  RestoreRegList(masm(), saved_double_registers, x1,
                 FrameDescription::double_registers_offset());

  // TODO(all): ARM copies a lot (if not all) of the last output frame onto the
  // stack, then pops it all into registers. Here, we try to load it directly
  // into the relevant registers. Is this correct? If so, we should improve the
  // ARM code.

  // Restore registers from the last output frame.
  // Note that lr is not in the list of saved_registers and will be restored
  // later. We can use it to hold the address of last output frame while
  // reloading the other registers.
  DCHECK(!saved_registers.IncludesAliasOf(lr));
  Register last_output_frame = lr;
  __ Mov(last_output_frame, current_frame);

  RestoreRegList(masm(), saved_registers, last_output_frame,
                 FrameDescription::registers_offset());

  Register continuation = x7;
  __ Ldr(continuation, MemOperand(last_output_frame,
                                  FrameDescription::continuation_offset()));
  __ Ldr(lr, MemOperand(last_output_frame, FrameDescription::pc_offset()));
  __ InitializeRootRegister();
  __ Br(continuation);
}

// Size of an entry of the second level deopt table.
// This is the code size generated by GeneratePrologue for one entry.
const int Deoptimizer::table_entry_size_ = kInstructionSize;

void Deoptimizer::TableEntryGenerator::GeneratePrologue() {
  UseScratchRegisterScope temps(masm());
  // The address at which the deopt table is entered should be in x16, the first
  // temp register allocated. We can't assert that the address is in there, but
  // we can check that it's the first allocated temp. Later, we'll also check
  // the computed entry_id is in the expected range.
  Register entry_addr = temps.AcquireX();
  Register entry_id = temps.AcquireX();
  DCHECK(entry_addr.Is(x16));
  DCHECK(entry_id.Is(x17));

  // Create a sequence of deoptimization entries.
  // Note that registers are still live when jumping to an entry.
  {
    InstructionAccurateScope scope(masm());

    Label start_of_table, end_of_table;
    __ bind(&start_of_table);
    for (int i = 0; i < count(); i++) {
      int start = masm()->pc_offset();
      USE(start);
      __ b(&end_of_table);
      DCHECK(masm()->pc_offset() - start == table_entry_size_);
    }
    __ bind(&end_of_table);

    // Get the address of the start of the table.
    DCHECK(is_int21(table_entry_size_ * count()));
    __ adr(entry_id, &start_of_table);

    // Compute the gap in bytes between the entry address, which should have
    // been left in entry_addr (x16) by CallForDeoptimization, and the start of
    // the table.
    __ sub(entry_id, entry_addr, entry_id);

    // Shift down to obtain the entry_id.
    DCHECK_EQ(table_entry_size_, kInstructionSize);
    __ lsr(entry_id, entry_id, kInstructionSizeLog2);
  }

  __ Push(padreg, entry_id);

  if (__ emit_debug_code()) {
    // Ensure the entry_id looks sensible, ie. 0 <= entry_id < count().
    __ Cmp(entry_id, count());
    __ Check(lo, AbortReason::kOffsetOutOfRange);
  }
}

bool Deoptimizer::PadTopOfStackRegister() { return true; }

void FrameDescription::SetCallerPc(unsigned offset, intptr_t value) {
  SetFrameSlot(offset, value);
}


void FrameDescription::SetCallerFp(unsigned offset, intptr_t value) {
  SetFrameSlot(offset, value);
}


void FrameDescription::SetCallerConstantPool(unsigned offset, intptr_t value) {
  // No embedded constant pool support.
  UNREACHABLE();
}


#undef __

}  // namespace internal
}  // namespace v8