wasm-linkage.h

// Copyright 2018 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.

#ifndef V8_WASM_WASM_LINKAGE_H_
#define V8_WASM_WASM_LINKAGE_H_

#include "src/assembler-arch.h"
#include "src/machine-type.h"
#include "src/signature.h"
#include "src/wasm/value-type.h"

namespace v8 {
namespace internal {
namespace wasm {

// TODO(wasm): optimize calling conventions to be both closer to C++ (to
// reduce adapter costs for fast WASM <-> C++ calls) and to be more efficient
// in general.

#if V8_TARGET_ARCH_IA32
// ===========================================================================
// == ia32 ===================================================================
// ===========================================================================
constexpr Register kGpParamRegisters[] = {esi, eax, edx, ecx};
constexpr Register kGpReturnRegisters[] = {eax, edx};
constexpr DoubleRegister kFpParamRegisters[] = {xmm1, xmm2, xmm3,
                                                xmm4, xmm5, xmm6};
constexpr DoubleRegister kFpReturnRegisters[] = {xmm1, xmm2};

#elif V8_TARGET_ARCH_X64
// ===========================================================================
// == x64 ====================================================================
// ===========================================================================
constexpr Register kGpParamRegisters[] = {rsi, rax, rdx, rcx, rbx, r9};
constexpr Register kGpReturnRegisters[] = {rax, rdx};
constexpr DoubleRegister kFpParamRegisters[] = {xmm1, xmm2, xmm3,
                                                xmm4, xmm5, xmm6};
constexpr DoubleRegister kFpReturnRegisters[] = {xmm1, xmm2};

#elif V8_TARGET_ARCH_ARM
// ===========================================================================
// == arm ====================================================================
// ===========================================================================
constexpr Register kGpParamRegisters[] = {r3, r0, r2, r6};
constexpr Register kGpReturnRegisters[] = {r0, r1};
// ARM d-registers must be in ascending order for correct allocation.
constexpr DoubleRegister kFpParamRegisters[] = {d0, d1, d2, d3, d4, d5, d6, d7};
constexpr DoubleRegister kFpReturnRegisters[] = {d0, d1};

#elif V8_TARGET_ARCH_ARM64
// ===========================================================================
// == arm64 ====================================================================
// ===========================================================================
constexpr Register kGpParamRegisters[] = {x7, x0, x2, x3, x4, x5, x6};
constexpr Register kGpReturnRegisters[] = {x0, x1};
constexpr DoubleRegister kFpParamRegisters[] = {d0, d1, d2, d3, d4, d5, d6, d7};
constexpr DoubleRegister kFpReturnRegisters[] = {d0, d1};

#elif V8_TARGET_ARCH_MIPS
// ===========================================================================
// == mips ===================================================================
// ===========================================================================
constexpr Register kGpParamRegisters[] = {a0, a2, a3};
constexpr Register kGpReturnRegisters[] = {v0, v1};
constexpr DoubleRegister kFpParamRegisters[] = {f2, f4, f6, f8, f10, f12, f14};
constexpr DoubleRegister kFpReturnRegisters[] = {f2, f4};

#elif V8_TARGET_ARCH_MIPS64
// ===========================================================================
// == mips64 =================================================================
// ===========================================================================
constexpr Register kGpParamRegisters[] = {a0, a2, a3, a4, a5, a6, a7};
constexpr Register kGpReturnRegisters[] = {v0, v1};
constexpr DoubleRegister kFpParamRegisters[] = {f2, f4, f6, f8, f10, f12, f14};
constexpr DoubleRegister kFpReturnRegisters[] = {f2, f4};

#elif V8_TARGET_ARCH_PPC || V8_TARGET_ARCH_PPC64
// ===========================================================================
// == ppc & ppc64 ============================================================
// ===========================================================================
constexpr Register kGpParamRegisters[] = {r10, r3, r5, r6, r7, r8, r9};
constexpr Register kGpReturnRegisters[] = {r3, r4};
constexpr DoubleRegister kFpParamRegisters[] = {d1, d2, d3, d4, d5, d6, d7, d8};
constexpr DoubleRegister kFpReturnRegisters[] = {d1, d2};

#elif V8_TARGET_ARCH_S390X
// ===========================================================================
// == s390x ==================================================================
// ===========================================================================
constexpr Register kGpParamRegisters[] = {r6, r2, r4, r5};
constexpr Register kGpReturnRegisters[] = {r2, r3};
constexpr DoubleRegister kFpParamRegisters[] = {d0, d2, d4, d6};
constexpr DoubleRegister kFpReturnRegisters[] = {d0, d2, d4, d6};

#elif V8_TARGET_ARCH_S390
// ===========================================================================
// == s390 ===================================================================
// ===========================================================================
constexpr Register kGpParamRegisters[] = {r6, r2, r4, r5};
constexpr Register kGpReturnRegisters[] = {r2, r3};
constexpr DoubleRegister kFpParamRegisters[] = {d0, d2};
constexpr DoubleRegister kFpReturnRegisters[] = {d0, d2};

#else
// ===========================================================================
// == unknown ================================================================
// ===========================================================================
// Do not use any registers, we will just always use the stack.
constexpr Register kGpParamRegisters[] = {};
constexpr Register kGpReturnRegisters[] = {};
constexpr DoubleRegister kFpParamRegisters[] = {};
constexpr DoubleRegister kFpReturnRegisters[] = {};

#endif

// The parameter index where the instance parameter should be placed in wasm
// call descriptors. This is used by the Int64Lowering::LowerNode method.
constexpr int kWasmInstanceParameterIndex = 0;

class LinkageAllocator {
 public:
  template <size_t kNumGpRegs, size_t kNumFpRegs>
  constexpr LinkageAllocator(const Register (&gp)[kNumGpRegs],
                             const DoubleRegister (&fp)[kNumFpRegs])
      : LinkageAllocator(gp, kNumGpRegs, fp, kNumFpRegs) {}

  constexpr LinkageAllocator(const Register* gp, int gpc,
                             const DoubleRegister* fp, int fpc)
      : gp_count_(gpc), gp_regs_(gp), fp_count_(fpc), fp_regs_(fp) {}

  bool CanAllocateGP() const { return gp_offset_ < gp_count_; }
  bool CanAllocateFP(MachineRepresentation rep) const {
#if V8_TARGET_ARCH_ARM
    switch (rep) {
      case MachineRepresentation::kFloat32:
        return fp_offset_ < fp_count_ && fp_regs_[fp_offset_].code() < 16;
      case MachineRepresentation::kFloat64:
        return extra_double_reg_ >= 0 || fp_offset_ < fp_count_;
      case MachineRepresentation::kSimd128:
        return ((fp_offset_ + 1) & ~1) + 1 < fp_count_;
      default:
        UNREACHABLE();
        return false;
    }
#endif
    return fp_offset_ < fp_count_;
  }

  int NextGpReg() {
    DCHECK_LT(gp_offset_, gp_count_);
    return gp_regs_[gp_offset_++].code();
  }

  int NextFpReg(MachineRepresentation rep) {
#if V8_TARGET_ARCH_ARM
    switch (rep) {
      case MachineRepresentation::kFloat32: {
        // Liftoff uses only even-numbered f32 registers, and encodes them using
        // the code of the corresponding f64 register. This limits the calling
        // interface to only using the even-numbered f32 registers.
        int d_reg_code = NextFpReg(MachineRepresentation::kFloat64);
        DCHECK_GT(16, d_reg_code);  // D-registers 16 - 31 can't split.
        return d_reg_code * 2;
      }
      case MachineRepresentation::kFloat64: {
        // Use the extra D-register if there is one.
        if (extra_double_reg_ >= 0) {
          int reg_code = extra_double_reg_;
          extra_double_reg_ = -1;
          return reg_code;
        }
        DCHECK_LT(fp_offset_, fp_count_);
        return fp_regs_[fp_offset_++].code();
      }
      case MachineRepresentation::kSimd128: {
        // Q-register must be an even-odd pair, so we must try to allocate at
        // the end, not using extra_double_reg_. If we are at an odd D-register,
        // skip past it (saving it to extra_double_reg_).
        DCHECK_LT(((fp_offset_ + 1) & ~1) + 1, fp_count_);
        int d_reg1_code = fp_regs_[fp_offset_++].code();
        if (d_reg1_code % 2 != 0) {
          // If we're misaligned then extra_double_reg_ must have been consumed.
          DCHECK_EQ(-1, extra_double_reg_);
          int odd_double_reg = d_reg1_code;
          d_reg1_code = fp_regs_[fp_offset_++].code();
          extra_double_reg_ = odd_double_reg;
        }
        // Combine the current D-register with the next to form a Q-register.
        int d_reg2_code = fp_regs_[fp_offset_++].code();
        DCHECK_EQ(0, d_reg1_code % 2);
        DCHECK_EQ(d_reg1_code + 1, d_reg2_code);
        USE(d_reg2_code);
        return d_reg1_code / 2;
      }
      default:
        UNREACHABLE();
    }
#else
    DCHECK_LT(fp_offset_, fp_count_);
    return fp_regs_[fp_offset_++].code();
#endif
  }

  // Stackslots are counted upwards starting from 0 (or the offset set by
  // {SetStackOffset}.
  int NumStackSlots(MachineRepresentation type) {
    return std::max(1, ElementSizeInBytes(type) / kPointerSize);
  }

  // Stackslots are counted upwards starting from 0 (or the offset set by
  // {SetStackOffset}. If {type} needs more than
  // one stack slot, the lowest used stack slot is returned.
  int NextStackSlot(MachineRepresentation type) {
    int num_stack_slots = NumStackSlots(type);
    int offset = stack_offset_;
    stack_offset_ += num_stack_slots;
    return offset;
  }

  // Set an offset for the stack slots returned by {NextStackSlot} and
  // {NumStackSlots}. Can only be called before any call to {NextStackSlot}.
  void SetStackOffset(int num) {
    DCHECK_LE(0, num);
    DCHECK_EQ(0, stack_offset_);
    stack_offset_ = num;
  }

  int NumStackSlots() const { return stack_offset_; }

 private:
  const int gp_count_;
  int gp_offset_ = 0;
  const Register* const gp_regs_;

  const int fp_count_;
  int fp_offset_ = 0;
  const DoubleRegister* const fp_regs_;

#if V8_TARGET_ARCH_ARM
  // Track fragments of registers below fp_offset_ here. There can only be one
  // extra double register.
  int extra_double_reg_ = -1;
#endif

  int stack_offset_ = 0;
};

}  // namespace wasm
}  // namespace internal
}  // namespace v8

#endif  // V8_WASM_WASM_LINKAGE_H_