[Liftoff] Support i64 constants

For local variables of type i64 and also for i64 constants, it makes
sense to store the constant value in the {VarState} instead of loading
the value into a register immediately. This also helps with some
instructions like i64 bitshifts, but also general patterns like
incrementing an i64 local variable by a fixed number.

R=ahaas@chromium.org

Bug: v8:6600
Change-Id: Ibed15228bbc53632dd3e60d7862ff2fbcb9832ca
Reviewed-on: https://chromium-review.googlesource.com/904443
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51179}

src/wasm/baseline/ia32/liftoff-assembler-ia32.h

@@ -545,8 +545,10 @@ void LiftoffAssembler::PushCallerFrameSlot(const VarState& src,
               ? (half == kLowWord ? src.reg().low() : src.reg().high())
               : src.reg());
       break;
-    case VarState::kI32Const:
-      push(Immediate(src.i32_const()));
+    case VarState::KIntConst:
+      // The high word is the sign extension of the low word.
+      push(Immediate(half == kLowWord ? src.i32_const()
+                                      : src.i32_const() >> 31));
       break;
   }
 }

src/wasm/baseline/liftoff-assembler.cc

@@ -42,26 +42,33 @@ class StackTransferRecipe {
       kStack,     // fill a register from a stack slot.
       kHalfStack  // fill one half of a register pair from half a stack slot.
     };
+
     LiftoffRegister dst;
     LoadKind kind;
     ValueType type;
-    uint32_t value;  // i32 constant value or stack index, depending on kind.
+    int32_t value;  // i32 constant value or stack index, depending on kind.
+
     // Named constructors.
     static RegisterLoad Const(LiftoffRegister dst, WasmValue constant) {
-      return {dst, kConstant, kWasmI32, constant.to_u32()};
+      if (constant.type() == kWasmI32) {
+        return {dst, kConstant, kWasmI32, constant.to_i32()};
+      }
+      DCHECK_EQ(kWasmI64, constant.type());
+      DCHECK_EQ(constant.to_i32_unchecked(), constant.to_i64_unchecked());
+      return {dst, kConstant, kWasmI64, constant.to_i32_unchecked()};
     }
-    static RegisterLoad Stack(LiftoffRegister dst, uint32_t stack_index,
+    static RegisterLoad Stack(LiftoffRegister dst, int32_t stack_index,
                               ValueType type) {
       return {dst, kStack, type, stack_index};
     }
     static RegisterLoad HalfStack(LiftoffRegister dst,
-                                  uint32_t half_stack_index) {
+                                  int32_t half_stack_index) {
       return {dst, kHalfStack, kWasmI32, half_stack_index};
     }
 
    private:
     RegisterLoad(LiftoffRegister dst, LoadKind kind, ValueType type,
-                 uint32_t value)
+                 int32_t value)
         : dst(dst), kind(kind), type(type), value(value) {}
   };
 
@@ -128,7 +135,9 @@ class StackTransferRecipe {
     for (RegisterLoad& rl : register_loads_) {
       switch (rl.kind) {
         case RegisterLoad::kConstant:
-          asm_->LoadConstant(rl.dst, WasmValue(rl.value));
+          asm_->LoadConstant(rl.dst, rl.type == kWasmI64
+                                         ? WasmValue(int64_t{rl.value})
+                                         : WasmValue(int32_t{rl.value}));
           break;
         case RegisterLoad::kStack:
           asm_->Fill(rl.dst, rl.value, rl.type);
@@ -157,15 +166,15 @@ class StackTransferRecipe {
           case VarState::kRegister:
             asm_->Spill(dst_index, src.reg(), src.type());
             break;
-          case VarState::kI32Const:
-            asm_->Spill(dst_index, WasmValue(src.i32_const()));
+          case VarState::KIntConst:
+            asm_->Spill(dst_index, src.constant());
             break;
         }
         break;
       case VarState::kRegister:
         LoadIntoRegister(dst.reg(), src, src_index);
         break;
-      case VarState::kI32Const:
+      case VarState::KIntConst:
         DCHECK_EQ(dst, src);
         break;
     }
@@ -182,8 +191,8 @@ class StackTransferRecipe {
         DCHECK_EQ(dst.reg_class(), src.reg_class());
         if (dst != src.reg()) MoveRegister(dst, src.reg(), src.type());
         break;
-      case VarState::kI32Const:
-        LoadConstant(dst, WasmValue(src.i32_const()));
+      case VarState::KIntConst:
+        LoadConstant(dst, src.constant());
         break;
     }
   }
@@ -205,8 +214,10 @@ class StackTransferRecipe {
         if (dst != src_half) MoveRegister(dst, src_half, kWasmI32);
         break;
       }
-      case VarState::kI32Const:
-        int32_t value = half == kLowWord ? src.i32_const() : 0;
+      case VarState::KIntConst:
+        int32_t value = src.i32_const();
+        // The high word is the sign extension of the low word.
+        if (half == kHighWord) value = value >> 31;
         LoadConstant(dst, WasmValue(value));
         break;
     }
@@ -382,9 +393,9 @@ LiftoffRegister LiftoffAssembler::PopToRegister(RegClass rc,
       DCHECK_EQ(rc, slot.reg_class());
       cache_state_.dec_used(slot.reg());
       return slot.reg();
-    case VarState::kI32Const: {
+    case VarState::KIntConst: {
       LiftoffRegister reg = GetUnusedRegister(rc, pinned);
-      LoadConstant(reg, WasmValue(slot.i32_const()));
+      LoadConstant(reg, slot.constant());
       return reg;
     }
   }
@@ -429,8 +440,8 @@ void LiftoffAssembler::Spill(uint32_t index) {
       Spill(index, slot.reg(), slot.type());
       cache_state_.dec_used(slot.reg());
       break;
-    case VarState::kI32Const:
-      Spill(index, WasmValue(slot.i32_const()));
+    case VarState::KIntConst:
+      Spill(index, slot.constant());
       break;
   }
   slot.MakeStack();
@@ -619,7 +630,7 @@ std::ostream& operator<<(std::ostream& os, VarState slot) {
       return os << "s";
     case VarState::kRegister:
       return os << slot.reg();
-    case VarState::kI32Const:
+    case VarState::KIntConst:
       return os << "c" << slot.i32_const();
   }
   UNREACHABLE();

src/wasm/baseline/liftoff-assembler.h

@@ -36,26 +36,27 @@ class LiftoffAssembler : public TurboAssembler {
 
   class VarState {
    public:
-    enum Location : uint8_t { kStack, kRegister, kI32Const };
+    enum Location : uint8_t { kStack, kRegister, KIntConst };
 
     explicit VarState(ValueType type) : loc_(kStack), type_(type) {}
     explicit VarState(ValueType type, LiftoffRegister r)
         : loc_(kRegister), type_(type), reg_(r) {
       DCHECK_EQ(r.reg_class(), reg_class_for(type));
     }
-    explicit VarState(ValueType type, uint32_t i32_const)
-        : loc_(kI32Const), type_(type), i32_const_(i32_const) {
+    explicit VarState(ValueType type, int32_t i32_const)
+        : loc_(KIntConst), type_(type), i32_const_(i32_const) {
       DCHECK(type_ == kWasmI32 || type_ == kWasmI64);
     }
 
     bool operator==(const VarState& other) const {
       if (loc_ != other.loc_) return false;
+      if (type_ != other.type_) return false;
       switch (loc_) {
         case kStack:
           return true;
         case kRegister:
           return reg_ == other.reg_;
-        case kI32Const:
+        case KIntConst:
           return i32_const_ == other.i32_const_;
       }
       UNREACHABLE();
@@ -65,16 +66,23 @@ class LiftoffAssembler : public TurboAssembler {
     bool is_gp_reg() const { return loc_ == kRegister && reg_.is_gp(); }
     bool is_fp_reg() const { return loc_ == kRegister && reg_.is_fp(); }
     bool is_reg() const { return loc_ == kRegister; }
-    bool is_const() const { return loc_ == kI32Const; }
+    bool is_const() const { return loc_ == KIntConst; }
 
     ValueType type() const { return type_; }
 
     Location loc() const { return loc_; }
 
-    uint32_t i32_const() const {
-      DCHECK_EQ(loc_, kI32Const);
+    int32_t i32_const() const {
+      DCHECK_EQ(loc_, KIntConst);
       return i32_const_;
     }
+    WasmValue constant() const {
+      DCHECK(type_ == kWasmI32 || type_ == kWasmI64);
+      DCHECK_EQ(loc_, KIntConst);
+      return type_ == kWasmI32 ? WasmValue(i32_const_)
+                               : WasmValue(int64_t{i32_const_});
+    }
+
     Register gp_reg() const { return reg().gp(); }
     DoubleRegister fp_reg() const { return reg().fp(); }
     LiftoffRegister reg() const {
@@ -93,7 +101,7 @@ class LiftoffAssembler : public TurboAssembler {
 
     union {
       LiftoffRegister reg_;  // used if loc_ == kRegister
-      uint32_t i32_const_;   // used if loc_ == kI32Const
+      int32_t i32_const_;    // used if loc_ == KIntConst
     };
   };
 

src/wasm/baseline/liftoff-compiler.cc

@@ -20,7 +20,7 @@ namespace internal {
 namespace wasm {
 
 constexpr auto kRegister = LiftoffAssembler::VarState::kRegister;
-constexpr auto kI32Const = LiftoffAssembler::VarState::kI32Const;
+constexpr auto KIntConst = LiftoffAssembler::VarState::KIntConst;
 constexpr auto kStack = LiftoffAssembler::VarState::kStack;
 
 namespace {
@@ -616,9 +616,18 @@ class LiftoffCompiler {
   }
 
   void I64Const(Decoder* decoder, Value* result, int64_t value) {
+    // The {VarState} stores constant values as int32_t, thus we only store
+    // 64-bit constants in this field if it fits in an int32_t. Larger values
+    // cannot be used as immediate value anyway, so we can also just put them in
+    // a register immediately.
+    int32_t value_i32 = static_cast<int32_t>(value);
+    if (value_i32 == value) {
+      __ cache_state()->stack_state.emplace_back(kWasmI64, value_i32);
+    } else {
       LiftoffRegister reg = __ GetUnusedRegister(reg_class_for(kWasmI64));
       __ LoadConstant(reg, WasmValue(value));
       __ PushRegister(kWasmI64, reg);
+    }
     CheckStackSizeLimit(decoder);
   }
 
@@ -664,7 +673,7 @@ class LiftoffCompiler {
       case kRegister:
         __ PushRegister(slot.type(), slot.reg());
         break;
-      case kI32Const:
+      case KIntConst:
         __ cache_state()->stack_state.emplace_back(operand.type,
                                                    slot.i32_const());
         break;
@@ -709,7 +718,7 @@ class LiftoffCompiler {
         target_slot = source_slot;
         if (is_tee) state.inc_used(target_slot.reg());
         break;
-      case kI32Const:
+      case KIntConst:
         __ DropStackSlot(&target_slot);
         target_slot = source_slot;
         break;

src/wasm/baseline/x64/liftoff-assembler-x64.h

@@ -23,8 +23,13 @@ constexpr int32_t kFirstStackSlotOffset =
     kConstantStackSpace + LiftoffAssembler::kStackSlotSize;
 
 inline Operand GetStackSlot(uint32_t index) {
-  return Operand(
-      rbp, -kFirstStackSlotOffset - index * LiftoffAssembler::kStackSlotSize);
+  int32_t offset = index * LiftoffAssembler::kStackSlotSize;
+  return Operand(rbp, -kFirstStackSlotOffset - offset);
+}
+
+inline Operand GetHalfStackSlot(uint32_t half_index) {
+  int32_t offset = half_index * (LiftoffAssembler::kStackSlotSize / 2);
+  return Operand(rbp, -kFirstStackSlotOffset - offset);
 }
 
 // TODO(clemensh): Make this a constexpr variable once Operand is constexpr.
@@ -255,6 +260,16 @@ void LiftoffAssembler::Spill(uint32_t index, WasmValue value) {
     case kWasmI32:
       movl(dst, Immediate(value.to_i32()));
       break;
+    case kWasmI64: {
+      // We could use movq, but this would require a temporary register. For
+      // simplicity (and to avoid potentially having to spill another register),
+      // we use two movl instructions.
+      int32_t low_word = static_cast<int32_t>(value.to_i64());
+      int32_t high_word = static_cast<int32_t>(value.to_i64() >> 32);
+      movl(dst, Immediate(low_word));
+      movl(liftoff::GetHalfStackSlot(2 * index + 1), Immediate(high_word));
+      break;
+    }
     case kWasmF32:
       movl(dst, Immediate(value.to_f32_boxed().get_bits()));
       break;
@@ -514,7 +529,7 @@ void LiftoffAssembler::PushCallerFrameSlot(const VarState& src,
     case VarState::kRegister:
       PushCallerFrameSlot(src.reg());
       break;
-    case VarState::kI32Const:
+    case VarState::KIntConst:
       pushq(Immediate(src.i32_const()));
       break;
   }