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

src/arm/macro-assembler-arm.cc

 // Copyright 2012 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.
 
 #include <limits.h>  // For LONG_MIN, LONG_MAX.
 
 #if V8_TARGET_ARCH_ARM
 
 #include "src/base/bits.h"
 #include "src/base/division-by-constant.h"
@@ skipping 1634 matching lines @@
     if (emit_debug_code()) {
       // Trash the registers to simulate an allocation failure.
       mov(result, Operand(0x7091));
       mov(scratch1, Operand(0x7191));
       mov(scratch2, Operand(0x7291));
     }
     jmp(gc_required);
     return;
   }
 
-  DCHECK(!result.is(scratch1));
-  DCHECK(!result.is(scratch2));
-  DCHECK(!scratch1.is(scratch2));
-  DCHECK(!scratch1.is(ip));
-  DCHECK(!scratch2.is(ip));
+  DCHECK(!AreAliased(result, scratch1, scratch2, ip));
 
   // Make object size into bytes.
   if ((flags & SIZE_IN_WORDS) != 0) {
     object_size *= kPointerSize;
   }
   DCHECK_EQ(0, object_size & kObjectAlignmentMask);
 
   // Check relative positions of allocation top and limit addresses.
   // The values must be adjacent in memory to allow the use of LDM.
   // Also, assert that the registers are numbered such that the values
   // are loaded in the correct order.
   ExternalReference allocation_top =
       AllocationUtils::GetAllocationTopReference(isolate(), flags);
   ExternalReference allocation_limit =
       AllocationUtils::GetAllocationLimitReference(isolate(), flags);
 
-  intptr_t top   =
-      reinterpret_cast<intptr_t>(allocation_top.address());
-  intptr_t limit =
-      reinterpret_cast<intptr_t>(allocation_limit.address());
+  intptr_t top = reinterpret_cast<intptr_t>(allocation_top.address());
+  intptr_t limit = reinterpret_cast<intptr_t>(allocation_limit.address());
   DCHECK((limit - top) == kPointerSize);
   DCHECK(result.code() < ip.code());
 
   // Set up allocation top address register.
-  Register topaddr = scratch1;
-  mov(topaddr, Operand(allocation_top));
-
+  Register top_address = scratch1;
   // This code stores a temporary value in ip. This is OK, as the code below
   // does not need ip for implicit literal generation.
+  Register alloc_limit = ip;
+  Register result_end = scratch2;
+  mov(top_address, Operand(allocation_top));
+
   if ((flags & RESULT_CONTAINS_TOP) == 0) {
-    // Load allocation top into result and allocation limit into ip.
-    ldm(ia, topaddr, result.bit() | ip.bit());
+    // Load allocation top into result and allocation limit into alloc_limit.
+    ldm(ia, top_address, result.bit() | alloc_limit.bit());
   } else {
     if (emit_debug_code()) {
-      // Assert that result actually contains top on entry. ip is used
-      // immediately below so this use of ip does not cause difference with
-      // respect to register content between debug and release mode.
-      ldr(ip, MemOperand(topaddr));
-      cmp(result, ip);
+      // Assert that result actually contains top on entry.
+      ldr(alloc_limit, MemOperand(top_address));
+      cmp(result, alloc_limit);
       Check(eq, kUnexpectedAllocationTop);
     }
-    // Load allocation limit into ip. Result already contains allocation top.
-    ldr(ip, MemOperand(topaddr, limit - top));
+    // Load allocation limit. Result already contains allocation top.
+    ldr(alloc_limit, MemOperand(top_address, limit - top));
   }
 
   if ((flags & DOUBLE_ALIGNMENT) != 0) {
     // Align the next allocation. Storing the filler map without checking top is
     // safe in new-space because the limit of the heap is aligned there.
     STATIC_ASSERT(kPointerAlignment * 2 == kDoubleAlignment);
-    and_(scratch2, result, Operand(kDoubleAlignmentMask), SetCC);
+    and_(result_end, result, Operand(kDoubleAlignmentMask), SetCC);
     Label aligned;
     b(eq, &aligned);
     if ((flags & PRETENURE) != 0) {
-      cmp(result, Operand(ip));
+      cmp(result, Operand(alloc_limit));
       b(hs, gc_required);
     }
-    mov(scratch2, Operand(isolate()->factory()->one_pointer_filler_map()));
-    str(scratch2, MemOperand(result, kDoubleSize / 2, PostIndex));
+    mov(result_end, Operand(isolate()->factory()->one_pointer_filler_map()));
+    str(result_end, MemOperand(result, kDoubleSize / 2, PostIndex));
     bind(&aligned);
   }
 
   // Calculate new top and bail out if new space is exhausted. Use result
   // to calculate the new top. We must preserve the ip register at this
   // point, so we cannot just use add().
   DCHECK(object_size > 0);
   Register source = result;
   Condition cond = al;
   int shift = 0;
   while (object_size != 0) {
     if (((object_size >> shift) & 0x03) == 0) {
       shift += 2;
     } else {
       int bits = object_size & (0xff << shift);
       object_size -= bits;
       shift += 8;
       Operand bits_operand(bits);
       DCHECK(bits_operand.instructions_required(this) == 1);
-      add(scratch2, source, bits_operand, SetCC, cond);
-      source = scratch2;
+      add(result_end, source, bits_operand, SetCC, cond);
+      source = result_end;
       cond = cc;
     }
   }
   b(cs, gc_required);
-  cmp(scratch2, Operand(ip));
+  cmp(result_end, Operand(alloc_limit));
   b(hi, gc_required);
-  str(scratch2, MemOperand(topaddr));
+  str(result_end, MemOperand(top_address));
 
   // Tag object if requested.
   if ((flags & TAG_OBJECT) != 0) {
     add(result, result, Operand(kHeapObjectTag));
   }
 }
 
 
 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.
       mov(result, Operand(0x7091));
       mov(scratch, Operand(0x7191));
       mov(result_end, Operand(0x7291));
     }
     jmp(gc_required);
     return;
   }
 
-  // Assert that the register arguments are different and that none of
-  // them are ip. ip is used explicitly in the code generated below.
-  DCHECK(!result.is(scratch));
-  DCHECK(!result.is(result_end));
-  DCHECK(!scratch.is(result_end));
-  DCHECK(!object_size.is(ip));
-  DCHECK(!result.is(ip));
-  DCHECK(!scratch.is(ip));
-  DCHECK(!result_end.is(ip));
+  // |object_size| and |result_end| may overlap if the DOUBLE_ALIGNMENT flag
+  // is not specified. Other registers must not overlap.
+  DCHECK(!AreAliased(object_size, result, scratch, ip));
+  DCHECK(!AreAliased(result_end, result, scratch, ip));
+  DCHECK((flags & DOUBLE_ALIGNMENT) == 0 || !object_size.is(result_end));
 
   // Check relative positions of allocation top and limit addresses.
   // The values must be adjacent in memory to allow the use of LDM.
   // Also, assert that the registers are numbered such that the values
   // are loaded in the correct order.
   ExternalReference allocation_top =
       AllocationUtils::GetAllocationTopReference(isolate(), flags);
   ExternalReference allocation_limit =
       AllocationUtils::GetAllocationLimitReference(isolate(), flags);
-  intptr_t top =
-      reinterpret_cast<intptr_t>(allocation_top.address());
-  intptr_t limit =
-      reinterpret_cast<intptr_t>(allocation_limit.address());
+  intptr_t top = reinterpret_cast<intptr_t>(allocation_top.address());
+  intptr_t limit = reinterpret_cast<intptr_t>(allocation_limit.address());
   DCHECK((limit - top) == kPointerSize);
   DCHECK(result.code() < ip.code());
 
-  // Set up allocation top address.
-  Register topaddr = scratch;
-  mov(topaddr, Operand(allocation_top));
-
+  // Set up allocation top address and allocation limit registers.
+  Register top_address = scratch;
   // This code stores a temporary value in ip. This is OK, as the code below
   // does not need ip for implicit literal generation.
+  Register alloc_limit = ip;
+  mov(top_address, Operand(allocation_top));
+
   if ((flags & RESULT_CONTAINS_TOP) == 0) {
-    // Load allocation top into result and allocation limit into ip.
-    ldm(ia, topaddr, result.bit() | ip.bit());
+    // Load allocation top into result and allocation limit into alloc_limit.
+    ldm(ia, top_address, result.bit() | alloc_limit.bit());
   } else {
     if (emit_debug_code()) {
-      // Assert that result actually contains top on entry. ip is used
-      // immediately below so this use of ip does not cause difference with
-      // respect to register content between debug and release mode.
-      ldr(ip, MemOperand(topaddr));
-      cmp(result, ip);
+      // Assert that result actually contains top on entry.
+      ldr(alloc_limit, MemOperand(top_address));
+      cmp(result, alloc_limit);
       Check(eq, kUnexpectedAllocationTop);
     }
-    // Load allocation limit into ip. Result already contains allocation top.
-    ldr(ip, MemOperand(topaddr, limit - top));
+    // Load allocation limit. Result already contains allocation top.
+    ldr(alloc_limit, MemOperand(top_address, limit - top));
   }
 
   if ((flags & DOUBLE_ALIGNMENT) != 0) {
     // Align the next allocation. Storing the filler map without checking top is
     // safe in new-space because the limit of the heap is aligned there.
     DCHECK(kPointerAlignment * 2 == kDoubleAlignment);
     and_(result_end, result, Operand(kDoubleAlignmentMask), SetCC);
     Label aligned;
     b(eq, &aligned);
     if ((flags & PRETENURE) != 0) {
-      cmp(result, Operand(ip));
+      cmp(result, Operand(alloc_limit));
       b(hs, gc_required);
     }
     mov(result_end, Operand(isolate()->factory()->one_pointer_filler_map()));
     str(result_end, MemOperand(result, kDoubleSize / 2, PostIndex));
     bind(&aligned);
   }
 
   // Calculate new top and bail out if new space is exhausted. Use result
   // to calculate the new top. Object size may be in words so a shift is
   // required to get the number of bytes.
   if ((flags & SIZE_IN_WORDS) != 0) {
     add(result_end, result, Operand(object_size, LSL, kPointerSizeLog2), SetCC);
   } else {
     add(result_end, result, Operand(object_size), SetCC);
   }
   b(cs, gc_required);
-  cmp(result_end, Operand(ip));
+  cmp(result_end, Operand(alloc_limit));
   b(hi, gc_required);
 
   // Update allocation top. result temporarily holds the new top.
   if (emit_debug_code()) {
     tst(result_end, Operand(kObjectAlignmentMask));
     Check(eq, kUnalignedAllocationInNewSpace);
   }
-  str(result_end, MemOperand(topaddr));
+  str(result_end, MemOperand(top_address));
 
   // Tag object if requested.
   if ((flags & TAG_OBJECT) != 0) {
     add(result, result, Operand(kHeapObjectTag));
   }
 }
 
 
 void MacroAssembler::AllocateTwoByteString(Register result,
                                            Register length,
@@ skipping 1852 matching lines @@
     }
   }
   if (mag.shift > 0) mov(result, Operand(result, ASR, mag.shift));
   add(result, result, Operand(dividend, LSR, 31));
 }
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM