PPC: [liftoff] Change FillStackSlotsWithZero to use bytes

Missed out ppc in https://crrev.com/c/1947350

Bug: v8:9909
Change-Id: I1cdd02b75fda093d279ec9f4e8d99835a3e6c962
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1950223Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65323}

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

@@ -146,36 +146,29 @@ 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);
+  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) {
-      StoreP(r0, liftoff::GetHalfStackSlot(
-                     GetStackOffsetFromIndex(index + offset), kLowWord));
-      StoreP(r0, liftoff::GetHalfStackSlot(
-                     GetStackOffsetFromIndex(index + offset), kHighWord));
+  if (size <= 36) {
+    // Special straight-line code for up to nine words. Generates one
+    // instruction per word.
+    for (uint32_t offset = 4; offset <= size; offset += 4) {
+      StoreP(r0, liftoff::GetHalfStackSlot(start + offset, kLowWord));
     }
   } else {
     // General case for bigger counts (9 instructions).
     // Use r4 for start address (inclusive), r5 for end address (exclusive).
     push(r4);
     push(r5);
-    subi(r4, fp,
-         Operand(liftoff::GetStackSlotOffset(
-             GetStackOffsetFromIndex(last_stack_slot))));
-    subi(r5, fp,
-         Operand(liftoff::GetStackSlotOffset(GetStackOffsetFromIndex(index)) -
-                 kStackSlotSize));
+    subi(r4, fp, Operand(liftoff::GetStackSlotOffset(start + size)));
+    subi(r5, fp, Operand(liftoff::GetStackSlotOffset(start)));
 
     Label loop;
     bind(&loop);