Reshuffle registers in JSConstructStub to avoid trashing costructor and new.target on fast path (so…

src/arm64/macro-assembler-arm64.cc

Index: src/arm64/macro-assembler-arm64.cc
diff --git a/src/arm64/macro-assembler-arm64.cc b/src/arm64/macro-assembler-arm64.cc
index 0bd28aa8b38d739ce8aa2323dca4af3f1bfa381a..845565d9deb3fd156af6e821345d89084448d341 100644
--- a/src/arm64/macro-assembler-arm64.cc
+++ b/src/arm64/macro-assembler-arm64.cc
@@ -3073,23 +3073,24 @@ void MacroAssembler::Allocate(int object_size,
   intptr_t limit = reinterpret_cast<intptr_t>(heap_allocation_limit.address());
   DCHECK((limit - top) == kPointerSize);
 
-  // Set up allocation top address and object size registers.
+  // Set up allocation top address and allocation limit registers.
   Register top_address = scratch1;
-  Register allocation_limit = scratch2;
+  Register alloc_limit = scratch2;
+  Register result_end = scratch3;
   Mov(top_address, Operand(heap_allocation_top));
 
   if ((flags & RESULT_CONTAINS_TOP) == 0) {
-    // Load allocation top into result and the allocation limit.
-    Ldp(result, allocation_limit, MemOperand(top_address));
+    // Load allocation top into result and allocation limit into alloc_limit.
+    Ldp(result, alloc_limit, MemOperand(top_address));
   } else {
     if (emit_debug_code()) {
       // Assert that result actually contains top on entry.
-      Ldr(scratch3, MemOperand(top_address));
-      Cmp(result, scratch3);
+      Ldr(alloc_limit, MemOperand(top_address));
+      Cmp(result, alloc_limit);
       Check(eq, kUnexpectedAllocationTop);
     }
-    // Load the allocation limit. 'result' already contains the allocation top.
-    Ldr(allocation_limit, MemOperand(top_address, limit - top));
+    // Load allocation limit. Result already contains allocation top.
+    Ldr(alloc_limit, MemOperand(top_address, limit - top));
   }
 
   // We can ignore DOUBLE_ALIGNMENT flags here because doubles and pointers have
@@ -3097,10 +3098,10 @@ void MacroAssembler::Allocate(int object_size,
   STATIC_ASSERT(kPointerAlignment == kDoubleAlignment);
 
   // Calculate new top and bail out if new space is exhausted.
-  Adds(scratch3, result, object_size);
-  Ccmp(scratch3, allocation_limit, CFlag, cc);
+  Adds(result_end, result, object_size);
+  Ccmp(result_end, alloc_limit, CFlag, cc);
   B(hi, gc_required);
-  Str(scratch3, MemOperand(top_address));
+  Str(result_end, MemOperand(top_address));
 
   // Tag the object if requested.
   if ((flags & TAG_OBJECT) != 0) {
@@ -3127,7 +3128,9 @@ void MacroAssembler::Allocate(Register object_size, Register result,
   UseScratchRegisterScope temps(this);
   Register scratch2 = temps.AcquireX();
 
-  DCHECK(!AreAliased(object_size, result, scratch, scratch2, result_end));
+  // |object_size| and |result_end| may overlap, other registers must not.
+  DCHECK(!AreAliased(object_size, result, scratch, scratch2));
+  DCHECK(!AreAliased(result_end, result, scratch, scratch2));
   DCHECK(object_size.Is64Bits() && result.Is64Bits() && scratch.Is64Bits() &&
          result_end.Is64Bits());
 
@@ -3141,23 +3144,23 @@ void MacroAssembler::Allocate(Register object_size, Register result,
   intptr_t limit = reinterpret_cast<intptr_t>(heap_allocation_limit.address());
   DCHECK((limit - top) == kPointerSize);
 
-  // Set up allocation top address and object size registers.
+  // Set up allocation top address and allocation limit registers.
   Register top_address = scratch;
-  Register allocation_limit = scratch2;
+  Register alloc_limit = scratch2;
   Mov(top_address, heap_allocation_top);
 
   if ((flags & RESULT_CONTAINS_TOP) == 0) {
-    // Load allocation top into result and the allocation limit.
-    Ldp(result, allocation_limit, MemOperand(top_address));
+    // Load allocation top into result and allocation limit into alloc_limit.
+    Ldp(result, alloc_limit, MemOperand(top_address));
   } else {
     if (emit_debug_code()) {
       // Assert that result actually contains top on entry.
-      Ldr(result_end, MemOperand(top_address));
-      Cmp(result, result_end);
+      Ldr(alloc_limit, MemOperand(top_address));
+      Cmp(result, alloc_limit);
       Check(eq, kUnexpectedAllocationTop);
     }
-    // Load the allocation limit. 'result' already contains the allocation top.
-    Ldr(allocation_limit, MemOperand(top_address, limit - top));
+    // Load allocation limit. Result already contains allocation top.
+    Ldr(alloc_limit, MemOperand(top_address, limit - top));
   }
 
   // We can ignore DOUBLE_ALIGNMENT flags here because doubles and pointers have
@@ -3176,7 +3179,7 @@ void MacroAssembler::Allocate(Register object_size, Register result,
     Check(eq, kUnalignedAllocationInNewSpace);
   }
 
-  Ccmp(result_end, allocation_limit, CFlag, cc);
+  Ccmp(result_end, alloc_limit, CFlag, cc);
   B(hi, gc_required);
   Str(result_end, MemOperand(top_address));