[liftoff] Change FillStackSlotsWithZero to use bytes

Bug: v8:9909
Change-Id: I997ae6f19c580f08eb9ff8ee039e0dd647091616
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1947350
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65320}

src/codegen/x64/assembler-x64.cc

@@ -1940,6 +1940,12 @@ void Assembler::emit_repmovs(int size) {
   emit(0xA5);
 }
 
+void Assembler::repstosl() {
+  EnsureSpace ensure_space(this);
+  emit(0xF3);
+  emit(0xAB);
+}
+
 void Assembler::repstosq() {
   EnsureSpace ensure_space(this);
   emit(0xF3);

src/codegen/x64/assembler-x64.h

@@ -544,6 +544,8 @@ class V8_EXPORT_PRIVATE Assembler : public AssemblerBase {
   void repmovsl() { emit_repmovs(kInt32Size); }
   void repmovsq() { emit_repmovs(kInt64Size); }
 
+  // Repeated store of doublewords (fill (E)CX bytes at ES:[(E)DI] with EAX).
+  void repstosl();
   // Repeated store of quadwords (fill RCX quadwords at [RDI] with RAX).
   void repstosq();
 

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

@@ -640,36 +640,29 @@ void LiftoffAssembler::FillI64Half(Register reg, uint32_t offset,
   ldr(reg, liftoff::GetHalfStackSlot(offset, half));
 }
 
-void LiftoffAssembler::FillStackSlotsWithZero(uint32_t index, uint32_t count) {
-  DCHECK_LT(0, count);
-  uint32_t last_stack_slot = index + count - 1;
-  RecordUsedSpillOffset(GetStackOffsetFromIndex(last_stack_slot));
+void LiftoffAssembler::FillStackSlotsWithZero(uint32_t start, uint32_t size) {
+  DCHECK_LT(0, size);
+  DCHECK_EQ(0, size % 4);
+  RecordUsedSpillOffset(start + size);
 
   // We need a zero reg. Always use r0 for that, and push it before to restore
   // its value afterwards.
   push(r0);
   mov(r0, Operand(0));
 
-  if (count <= 5) {
-    // Special straight-line code for up to five slots. Generates two
-    // instructions per slot.
-    for (uint32_t offset = 0; offset < count; ++offset) {
-      str(r0, liftoff::GetHalfStackSlot(GetStackOffsetFromIndex(index + offset),
-                                        kLowWord));
-      str(r0, liftoff::GetHalfStackSlot(GetStackOffsetFromIndex(index + offset),
-                                        kHighWord));
+  if (size <= 36) {
+    // Special straight-line code for up to 9 words. Generates one
+    // instruction per word.
+    for (uint32_t offset = 4; offset <= size; offset += 4) {
+      str(r0, liftoff::GetHalfStackSlot(start + offset, kLowWord));
     }
   } else {
     // General case for bigger counts (9 instructions).
     // Use r1 for start address (inclusive), r2 for end address (exclusive).
     push(r1);
     push(r2);
-    sub(r1, fp,
-        Operand(liftoff::GetStackSlotOffset(
-            GetStackOffsetFromIndex(last_stack_slot))));
-    sub(r2, fp,
-        Operand(liftoff::GetStackSlotOffset(GetStackOffsetFromIndex(index)) -
-                kStackSlotSize));
+    sub(r1, fp, Operand(liftoff::GetStackSlotOffset(start + size)));
+    sub(r2, fp, Operand(liftoff::GetStackSlotOffset(start)));
 
     Label loop;
     bind(&loop);

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

@@ -398,39 +398,52 @@ void LiftoffAssembler::FillI64Half(Register, uint32_t offset, RegPairHalf) {
   UNREACHABLE();
 }
 
-void LiftoffAssembler::FillStackSlotsWithZero(uint32_t index, uint32_t count) {
-  DCHECK_LT(0, count);
-  uint32_t last_stack_slot = index + count - 1;
-  RecordUsedSpillOffset(GetStackOffsetFromIndex(last_stack_slot));
-
-  int max_stp_offset =
-      -liftoff::GetStackSlotOffset(GetStackOffsetFromIndex(index + count - 1));
-  if (count <= 12 && IsImmLSPair(max_stp_offset, kXRegSizeLog2)) {
+void LiftoffAssembler::FillStackSlotsWithZero(uint32_t start, uint32_t size) {
+  DCHECK_LT(0, size);
+  DCHECK_EQ(0, size % 4);
+  RecordUsedSpillOffset(start + size);
+
+  int max_stp_offset = -liftoff::GetStackSlotOffset(start + size);
+  if (size <= 12 * kStackSlotSize &&
+      IsImmLSPair(max_stp_offset, kXRegSizeLog2)) {
     // Special straight-line code for up to 12 slots. Generates one
-    // instruction per two slots (<= 6 instructions total).
-    for (; count > 1; count -= 2) {
+    // instruction per two slots (<= 7 instructions total).
     STATIC_ASSERT(kStackSlotSize == kSystemPointerSize);
-      stp(xzr, xzr,
-          liftoff::GetStackSlot(GetStackOffsetFromIndex(index + count - 1)));
+    uint32_t remainder = size;
+    for (; remainder >= 2 * kStackSlotSize; remainder -= 2 * kStackSlotSize) {
+      stp(xzr, xzr, liftoff::GetStackSlot(start + remainder));
     }
-    DCHECK(count == 0 || count == 1);
-    if (count) {
-      str(xzr, liftoff::GetStackSlot(GetStackOffsetFromIndex(index)));
+
+    DCHECK_GE(12, remainder);
+    switch (remainder) {
+      case 12:
+        str(xzr, liftoff::GetStackSlot(start + remainder));
+        strh(xzr, liftoff::GetStackSlot(start + remainder - 8));
+        break;
+      case 8:
+        str(xzr, liftoff::GetStackSlot(start + remainder));
+        break;
+      case 4:
+        strh(xzr, liftoff::GetStackSlot(start + remainder));
+        break;
+      case 0:
+        break;
+      default:
+        UNREACHABLE();
     }
   } else {
     // General case for bigger counts (5-8 instructions).
     UseScratchRegisterScope temps(this);
     Register address_reg = temps.AcquireX();
     // This {Sub} might use another temp register if the offset is too large.
-    Sub(address_reg, fp,
-        liftoff::GetStackSlotOffset(GetStackOffsetFromIndex(last_stack_slot)));
+    Sub(address_reg, fp, liftoff::GetStackSlotOffset(start + size));
     Register count_reg = temps.AcquireX();
-    Mov(count_reg, count);
+    Mov(count_reg, size / 4);
 
     Label loop;
     bind(&loop);
     sub(count_reg, count_reg, 1);
-    str(xzr, MemOperand(address_reg, kSystemPointerSize, PostIndex));
+    strh(xzr, MemOperand(address_reg, kSystemPointerSize, PostIndex));
     cbnz(count_reg, &loop);
   }
 }

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

@@ -503,21 +503,16 @@ void LiftoffAssembler::FillI64Half(Register reg, uint32_t offset,
   mov(reg, liftoff::GetHalfStackSlot(offset, half));
 }
 
-void LiftoffAssembler::FillStackSlotsWithZero(uint32_t index, uint32_t count) {
-  DCHECK_LT(0, count);
-  uint32_t last_stack_slot = index + count - 1;
-  RecordUsedSpillOffset(GetStackOffsetFromIndex(last_stack_slot));
-
-  if (count <= 2) {
-    // Special straight-line code for up to two slots (6-9 bytes per word:
-    // C7 <1-4 bytes operand> <4 bytes imm>, makes 12-18 bytes per slot).
-    for (uint32_t offset = 0; offset < count; ++offset) {
-      mov(liftoff::GetHalfStackSlot(GetStackOffsetFromIndex(index + offset),
-                                    kLowWord),
-          Immediate(0));
-      mov(liftoff::GetHalfStackSlot(GetStackOffsetFromIndex(index + offset),
-                                    kHighWord),
-          Immediate(0));
+void LiftoffAssembler::FillStackSlotsWithZero(uint32_t start, uint32_t size) {
+  DCHECK_LT(0, size);
+  DCHECK_EQ(0, size % 4);
+  RecordUsedSpillOffset(start + size);
+
+  if (size <= 12) {
+    // Special straight-line code for up to three words (6-9 bytes per word:
+    // C7 <1-4 bytes operand> <4 bytes imm>, makes 18-27 bytes total).
+    for (uint32_t offset = 4; offset <= size; offset += 4) {
+      mov(liftoff::GetHalfStackSlot(start + offset, kLowWord), Immediate(0));
     }
   } else {
     // General case for bigger counts.
@@ -527,10 +522,10 @@ void LiftoffAssembler::FillStackSlotsWithZero(uint32_t index, uint32_t count) {
     push(eax);
     push(ecx);
     push(edi);
-    lea(edi, liftoff::GetStackSlot(GetStackOffsetFromIndex(last_stack_slot)));
+    lea(edi, liftoff::GetStackSlot(start + size));
     xor_(eax, eax);
-    // Number of words is number of slots times two.
-    mov(ecx, Immediate(count * 2));
+    // Size is in bytes, convert to doublewords (4-bytes).
+    mov(ecx, Immediate(size / 4));
     rep_stos();
     pop(edi);
     pop(ecx);

src/wasm/baseline/liftoff-assembler.h

@@ -286,12 +286,14 @@ class LiftoffAssembler : public TurboAssembler {
   LiftoffRegister PopToRegister(LiftoffRegList pinned = {});
 
   uint32_t NextSpillOffset(ValueType type) {
+    return TopSpillOffset() + SlotSizeForType(type);
+  }
+
+  uint32_t TopSpillOffset() {
     if (cache_state_.stack_state.empty()) {
-      return SlotSizeForType(type);
+      return 0;
     }
-    VarState last = cache_state_.stack_state.back();
-    uint32_t offset = last.offset() + SlotSizeForType(type);
-    return offset;
+    return cache_state_.stack_state.back().offset();
   }
 
   void PushRegister(ValueType type, LiftoffRegister reg) {

src/wasm/baseline/liftoff-compiler.cc

@@ -478,16 +478,18 @@ class LiftoffCompiler {
     for (uint32_t param_idx = 0; param_idx < num_params; ++param_idx) {
       input_idx += ProcessParameter(__ local_type(param_idx), input_idx);
     }
+    uint32_t params_size = __ TopSpillOffset();
     DCHECK_EQ(input_idx, descriptor_->InputCount());
 
     // Initialize locals beyond parameters.
     if (SpillLocalsInitially(decoder, num_params)) {
-      __ FillStackSlotsWithZero(num_params, __ num_locals() - num_params);
       for (uint32_t param_idx = num_params; param_idx < __ num_locals();
            ++param_idx) {
         ValueType type = decoder->GetLocalType(param_idx);
         __ PushStack(type);
       }
+      uint32_t spill_size = __ TopSpillOffset();
+      __ FillStackSlotsWithZero(params_size, spill_size);
     } else {
       for (uint32_t param_idx = num_params; param_idx < __ num_locals();
            ++param_idx) {

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

@@ -616,28 +616,23 @@ void LiftoffAssembler::FillI64Half(Register reg, uint32_t offset,
   lw(reg, liftoff::GetHalfStackSlot(offset, half));
 }
 
-void LiftoffAssembler::FillStackSlotsWithZero(uint32_t index, uint32_t count) {
-  DCHECK_LT(0, count);
-  uint32_t last_stack_slot = index + count - 1;
-  RecordUsedSpillOffset(GetStackOffsetFromIndex(last_stack_slot));
-
-  if (count <= 12) {
-    // Special straight-line code for up to 12 slots. Generates one
-    // instruction per slot (<=12 instructions total).
-    for (uint32_t offset = 0; offset < count; ++offset) {
-      Sw(zero_reg,
-         liftoff::GetStackSlot(GetStackOffsetFromIndex(index + offset)));
+void LiftoffAssembler::FillStackSlotsWithZero(uint32_t start, uint32_t size) {
+  DCHECK_LT(0, size);
+  DCHECK_EQ(0, size % 4);
+  RecordUsedSpillOffset(start + size);
+
+  if (size <= 48) {
+    // Special straight-line code for up to 12 words. Generates one
+    // instruction per word (<=12 instructions total).
+    for (uint32_t offset = 4; offset <= size; offset += 4) {
+      Sw(zero_reg, liftoff::GetStackSlot(start + offset));
     }
   } else {
     // General case for bigger counts (12 instructions).
     // Use a0 for start address (inclusive), a1 for end address (exclusive).
     Push(a1, a0);
-    Addu(a0, fp,
-         Operand(-liftoff::GetStackSlotOffset(
-             GetStackOffsetFromIndex(last_stack_slot))));
-    Addu(a1, fp,
-         Operand(-liftoff::GetStackSlotOffset(GetStackOffsetFromIndex(index)) +
-                 kStackSlotSize));
+    Addu(a0, fp, Operand(-liftoff::GetStackSlotOffset(start + size)));
+    Addu(a1, fp, Operand(-liftoff::GetStackSlotOffset(start)));
 
     Label loop;
     bind(&loop);

src/wasm/baseline/mips64/liftoff-assembler-mips64.h

@@ -524,28 +524,27 @@ void LiftoffAssembler::FillI64Half(Register, uint32_t offset, RegPairHalf) {
   UNREACHABLE();
 }
 
-void LiftoffAssembler::FillStackSlotsWithZero(uint32_t index, uint32_t count) {
-  DCHECK_LT(0, count);
-  uint32_t last_stack_slot = index + count - 1;
-  RecordUsedSpillOffset(GetStackOffsetFromIndex(last_stack_slot));
+void LiftoffAssembler::FillStackSlotsWithZero(uint32_t start, uint32_t size) {
+  DCHECK_LT(0, size);
+  RecordUsedSpillOffset(start + size);
 
-  if (count <= 12) {
+  if (size <= 12 * kStackSlotSize) {
     // Special straight-line code for up to 12 slots. Generates one
     // instruction per slot (<= 12 instructions total).
-    for (uint32_t offset = 0; offset < count; ++offset) {
-      Sd(zero_reg,
-         liftoff::GetStackSlot(GetStackOffsetFromIndex(index + offset)));
+    uint32_t remainder = size;
+    for (; remainder >= kStackSlotSize; remainder -= kStackSlotSize) {
+      Sd(zero_reg, liftoff::GetStackSlot(start + remainder));
+    }
+    DCHECK(remainder == 4 || remainder == 0);
+    if (remainder) {
+      Sw(zero_reg, liftoff::GetStackSlot(start + remainder));
     }
   } else {
     // General case for bigger counts (12 instructions).
     // Use a0 for start address (inclusive), a1 for end address (exclusive).
     Push(a1, a0);
-    Daddu(a0, fp,
-          Operand(-liftoff::GetStackSlotOffset(
-              GetStackOffsetFromIndex(last_stack_slot))));
-    Daddu(a1, fp,
-          Operand(-liftoff::GetStackSlotOffset(GetStackOffsetFromIndex(index)) +
-                  kStackSlotSize));
+    Daddu(a0, fp, Operand(-liftoff::GetStackSlotOffset(start + end)));
+    Daddu(a1, fp, Operand(-liftoff::GetStackSlotOffset(start)));
 
     Label loop;
     bind(&loop);

src/wasm/baseline/s390/liftoff-assembler-s390.h

@@ -145,36 +145,34 @@ void LiftoffAssembler::FillI64Half(Register, uint32_t offset, RegPairHalf) {
   bailout(kUnsupportedArchitecture, "FillI64Half");
 }
 
-void LiftoffAssembler::FillStackSlotsWithZero(uint32_t index, uint32_t count) {
-  DCHECK_LT(0, count);
-  uint32_t last_stack_slot = index + count - 1;
-  RecordUsedSpillOffset(last_stack_slot);
+void LiftoffAssembler::FillStackSlotsWithZero(uint32_t start, uint32_t size) {
+  DCHECK_LT(0, size);
+  RecordUsedSpillOffset(start + size);
 
   // We need a zero reg. Always use r0 for that, and push it before to restore
   // its value afterwards.
   push(r0);
   mov(r0, Operand(0));
 
-  if (count <= 5) {
+  if (size <= 5 * kStackSlotSize) {
     // Special straight-line code for up to five slots. Generates two
     // instructions per slot.
-    for (uint32_t offset = 0; offset < count; ++offset) {
-      StoreP(r0, liftoff::GetHalfStackSlot(
-                     GetStackOffsetFromIndex(index + offset), kLowWord));
-      StoreP(r0, liftoff::GetHalfStackSlot(
-                     GetStackOffsetFromIndex(index + offset), kHighWord));
+    uint32_t remainder = size;
+    for (; remainder >= kStackSlotSize; remainder -= kStackSlotSize) {
+      StoreP(r0, liftoff::GetHalfStackSlot(start + remainder, kLowWord));
+      StoreP(r0, liftoff::GetHalfStackSlot(start + remainder, kHighWord));
+    }
+    DCHECK(remainder == 4 || remainder == 0);
+    if (remainder) {
+      StoreP(r0, liftoff::GetHalfStackSlot(start + remainder, kLowWord));
     }
   } else {
     // General case for bigger counts (9 instructions).
     // Use r3 for start address (inclusive), r4 for end address (exclusive).
     push(r3);
     push(r4);
-    SubP(r3, fp,
-         Operand(liftoff::GetStackSlotOffset(
-             GetStackOffsetFromIndex(last_stack_slot))));
-    SubP(r4, fp,
-         Operand(liftoff::GetStackSlotOffset(GetStackOffsetFromIndex(index)) -
-                 kStackSlotSize));
+    SubP(r3, fp, Operand(liftoff::GetStackSlotOffset(start + remainder)));
+    SubP(r4, fp, Operand(liftoff::GetStackSlotOffset(start)));
 
     Label loop;
     bind(&loop);

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

@@ -445,31 +445,34 @@ void LiftoffAssembler::FillI64Half(Register, uint32_t offset, RegPairHalf) {
   UNREACHABLE();
 }
 
-void LiftoffAssembler::FillStackSlotsWithZero(uint32_t index, uint32_t count) {
-  DCHECK_LT(0, count);
-  uint32_t last_stack_slot = index + count - 1;
-  RecordUsedSpillOffset(
-      LiftoffAssembler::GetStackOffsetFromIndex(last_stack_slot));
+void LiftoffAssembler::FillStackSlotsWithZero(uint32_t start, uint32_t size) {
+  DCHECK_LT(0, size);
+  RecordUsedSpillOffset(start + size);
 
-  if (count <= 3) {
+  if (size <= 3 * kStackSlotSize) {
     // Special straight-line code for up to three slots
-    // (7-10 bytes per slot: REX C7 <1-4 bytes op> <4 bytes imm>).
-    for (uint32_t offset = 0; offset < count; ++offset) {
-      movq(liftoff::GetStackSlot(GetStackOffsetFromIndex(index + offset)),
-           Immediate(0));
+    // (7-10 bytes per slot: REX C7 <1-4 bytes op> <4 bytes imm>),
+    // And a movd (6-9 byte) when size % 8 != 0;
+    uint32_t remainder = size;
+    for (; remainder >= kStackSlotSize; remainder -= kStackSlotSize) {
+      movq(liftoff::GetStackSlot(start + remainder), Immediate(0));
+    }
+    DCHECK(remainder == 4 || remainder == 0);
+    if (remainder) {
+      movl(liftoff::GetStackSlot(start + remainder), Immediate(0));
     }
   } else {
     // General case for bigger counts.
-    // This sequence takes 20-23 bytes (3 for pushes, 4-7 for lea, 2 for xor, 5
-    // for mov, 3 for repstosq, 3 for pops).
-    // From intel manual: repstosq fills RCX quadwords at [RDI] with RAX.
+    // This sequence takes 19-22 bytes (3 for pushes, 4-7 for lea, 2 for xor, 5
+    // for mov, 2 for repstosl, 3 for pops).
     pushq(rax);
     pushq(rcx);
     pushq(rdi);
-    leaq(rdi, liftoff::GetStackSlot(GetStackOffsetFromIndex(last_stack_slot)));
+    leaq(rdi, liftoff::GetStackSlot(start + size));
     xorl(rax, rax);
-    movl(rcx, Immediate(count));
-    repstosq();
+    // Convert size (bytes) to doublewords (4-bytes).
+    movl(rcx, Immediate(size / 4));
+    repstosl();
     popq(rdi);
     popq(rcx);
     popq(rax);

test/cctest/test-disasm-x64.cc

@@ -182,6 +182,7 @@ TEST(DisasmX64) {
   __ decq(rdx);
   __ cdq();
 
+  __ repstosl();
   __ repstosq();
 
   __ nop();