[liftoff] Skip write barrier for storing Smis

There is no need for write barriers if the stored value is known to be a
Smi.

R=thibaudm@chromium.org

Bug: v8:11453
Change-Id: Id1cf306b246686c245d1be5f72c46b54ba9829ca
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2707172Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72903}

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

@@ -720,7 +720,8 @@ void LiftoffAssembler::StoreTaggedPointer(Register dst_addr,
                                           Register offset_reg,
                                           int32_t offset_imm,
                                           LiftoffRegister src,
-                                          LiftoffRegList pinned) {
+                                          LiftoffRegList pinned,
+                                          SkipWriteBarrier skip_write_barrier) {
   STATIC_ASSERT(kTaggedSize == kInt32Size);
   Register actual_offset_reg = offset_reg;
   if (offset_reg != no_reg && offset_imm != 0) {
@@ -733,6 +734,9 @@ void LiftoffAssembler::StoreTaggedPointer(Register dst_addr,
                           ? MemOperand(dst_addr, offset_imm)
                           : MemOperand(dst_addr, actual_offset_reg);
   str(src.gp(), dst_op);
+
+  if (skip_write_barrier) return;
+
   // The write barrier.
   Label write_barrier;
   Label exit;

src/wasm/baseline/arm64/liftoff-assembler-arm64.h

@@ -444,12 +444,16 @@ void LiftoffAssembler::StoreTaggedPointer(Register dst_addr,
                                           Register offset_reg,
                                           int32_t offset_imm,
                                           LiftoffRegister src,
-                                          LiftoffRegList pinned) {
+                                          LiftoffRegList pinned,
+                                          SkipWriteBarrier skip_write_barrier) {
   // Store the value.
   UseScratchRegisterScope temps(this);
   MemOperand dst_op =
       liftoff::GetMemOp(this, &temps, dst_addr, offset_reg, offset_imm);
   StoreTaggedField(src.gp(), dst_op);
+
+  if (skip_write_barrier) return;
+
   // The write barrier.
   Label write_barrier;
   Label exit;

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

@@ -344,16 +344,19 @@ void LiftoffAssembler::StoreTaggedPointer(Register dst_addr,
                                           Register offset_reg,
                                           int32_t offset_imm,
                                           LiftoffRegister src,
-                                          LiftoffRegList pinned) {
+                                          LiftoffRegList pinned,
+                                          SkipWriteBarrier skip_write_barrier) {
   DCHECK_GE(offset_imm, 0);
   DCHECK_LE(offset_imm, std::numeric_limits<int32_t>::max());
   STATIC_ASSERT(kTaggedSize == kInt32Size);
-  Register scratch = pinned.set(GetUnusedRegister(kGpReg, pinned)).gp();
   Operand dst_op = offset_reg == no_reg
                        ? Operand(dst_addr, offset_imm)
                        : Operand(dst_addr, offset_reg, times_1, offset_imm);
   mov(dst_op, src.gp());
 
+  if (skip_write_barrier) return;
+
+  Register scratch = pinned.set(GetUnusedRegister(kGpReg, pinned)).gp();
   Label write_barrier;
   Label exit;
   CheckPageFlag(dst_addr, scratch,

src/wasm/baseline/liftoff-assembler.h

@@ -609,9 +609,14 @@ class LiftoffAssembler : public TurboAssembler {
   inline void LoadTaggedPointer(Register dst, Register src_addr,
                                 Register offset_reg, int32_t offset_imm,
                                 LiftoffRegList pinned);
+  enum SkipWriteBarrier : bool {
+    kSkipWriteBarrier = true,
+    kNoSkipWriteBarrier = false
+  };
   inline void StoreTaggedPointer(Register dst_addr, Register offset_reg,
                                  int32_t offset_imm, LiftoffRegister src,
-                                 LiftoffRegList pinned);
+                                 LiftoffRegList pinned,
+                                 SkipWriteBarrier = kNoSkipWriteBarrier);
   inline void LoadFixedArrayLengthAsInt32(LiftoffRegister dst, Register array,
                                           LiftoffRegList pinned) {
     int offset = FixedArray::kLengthOffset - kHeapObjectTag;

src/wasm/baseline/liftoff-compiler.cc

@@ -3570,7 +3570,7 @@ class LiftoffCompiler {
     __ StoreTaggedPointer(
         values_array, no_reg,
         wasm::ObjectAccess::ElementOffsetInTaggedFixedArray(*index_in_array),
-        tmp_reg, pinned);
+        tmp_reg, pinned, LiftoffAssembler::kSkipWriteBarrier);
 
     // Get the upper half word into tmp_reg and extend to a Smi.
     --*index_in_array;
@@ -3579,7 +3579,7 @@ class LiftoffCompiler {
     __ StoreTaggedPointer(
         values_array, no_reg,
         wasm::ObjectAccess::ElementOffsetInTaggedFixedArray(*index_in_array),
-        tmp_reg, pinned);
+        tmp_reg, pinned, LiftoffAssembler::kSkipWriteBarrier);
   }
 
   void StoreExceptionValue(ValueType type, Register values_array,
@@ -3641,11 +3641,6 @@ class LiftoffCompiler {
     }
     DCHECK_EQ(0, index);
 
-    // Since we need to call another builtin before the final use of the values
-    // array, put the reference on the stack, such that it survives the builtin
-    // call.
-    __ PushRegister(kPointerValueType, values_array);
-
     // Load the exception tag.
     DEBUG_CODE_COMMENT("load exception tag");
     Register exception_tag =
@@ -3655,9 +3650,6 @@ class LiftoffCompiler {
         exception_tag, exception_tag, no_reg,
         wasm::ObjectAccess::ElementOffsetInTaggedFixedArray(imm.index), {});
 
-    // Pop the values array reference back into a register.
-    values_array = __ PopToRegister(pinned);
-
     // Finally, call WasmThrow.
     DEBUG_CODE_COMMENT("call WasmThrow builtin");
     compiler::CallDescriptor* throw_descriptor =

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

@@ -335,13 +335,16 @@ void LiftoffAssembler::StoreTaggedPointer(Register dst_addr,
                                           Register offset_reg,
                                           int32_t offset_imm,
                                           LiftoffRegister src,
-                                          LiftoffRegList pinned) {
+                                          LiftoffRegList pinned,
+                                          SkipWriteBarrier skip_write_barrier) {
   DCHECK_GE(offset_imm, 0);
-  Register scratch = pinned.set(GetUnusedRegister(kGpReg, pinned)).gp();
   Operand dst_op = liftoff::GetMemOp(this, dst_addr, offset_reg,
                                      static_cast<uint32_t>(offset_imm));
   StoreTaggedField(dst_op, src.gp());
 
+  if (skip_write_barrier) return;
+
+  Register scratch = pinned.set(GetUnusedRegister(kGpReg, pinned)).gp();
   Label write_barrier;
   Label exit;
   CheckPageFlag(dst_addr, scratch,