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

src/arm64/macro-assembler-arm64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #if V8_TARGET_ARCH_ARM64
 
 #include "src/base/bits.h"
 #include "src/base/division-by-constant.h"
 #include "src/bootstrapper.h"
 #include "src/codegen.h"
@@ skipping 3055 matching lines @@
   // Check relative positions of allocation top and limit addresses.
   // The values must be adjacent in memory to allow the use of LDP.
   ExternalReference heap_allocation_top =
       AllocationUtils::GetAllocationTopReference(isolate(), flags);
   ExternalReference heap_allocation_limit =
       AllocationUtils::GetAllocationLimitReference(isolate(), flags);
   intptr_t top = reinterpret_cast<intptr_t>(heap_allocation_top.address());
   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
   // the same alignment on ARM64.
   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) {
     ObjectTag(result, result);
   }
 }
 
 
 void MacroAssembler::Allocate(Register object_size, Register result,
                               Register result_end, Register scratch,
                               Label* gc_required, AllocationFlags flags) {
   if (!FLAG_inline_new) {
     if (emit_debug_code()) {
       // Trash the registers to simulate an allocation failure.
       // We apply salt to the original zap value to easily spot the values.
       Mov(result, (kDebugZapValue & ~0xffL) | 0x11L);
       Mov(scratch, (kDebugZapValue & ~0xffL) | 0x21L);
       Mov(result_end, (kDebugZapValue & ~0xffL) | 0x21L);
     }
     B(gc_required);
     return;
   }
 
   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());
 
   // Check relative positions of allocation top and limit addresses.
   // The values must be adjacent in memory to allow the use of LDP.
   ExternalReference heap_allocation_top =
       AllocationUtils::GetAllocationTopReference(isolate(), flags);
   ExternalReference heap_allocation_limit =
       AllocationUtils::GetAllocationLimitReference(isolate(), flags);
   intptr_t top = reinterpret_cast<intptr_t>(heap_allocation_top.address());
   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
   // the same alignment on ARM64.
   STATIC_ASSERT(kPointerAlignment == kDoubleAlignment);
 
   // Calculate new top and bail out if new space is exhausted
   if ((flags & SIZE_IN_WORDS) != 0) {
     Adds(result_end, result, Operand(object_size, LSL, kPointerSizeLog2));
   } else {
     Adds(result_end, result, object_size);
   }
 
   if (emit_debug_code()) {
     Tst(result_end, kObjectAlignmentMask);
     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));
 
   // Tag the object if requested.
   if ((flags & TAG_OBJECT) != 0) {
     ObjectTag(result, result);
   }
 }
 
 
@@ skipping 1873 matching lines @@
 }
 
 
 #undef __
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM64