[crankshaft] Fragmentation-free allocation folding.

src/mips/macro-assembler-mips.cc

Index: src/mips/macro-assembler-mips.cc
diff --git a/src/mips/macro-assembler-mips.cc b/src/mips/macro-assembler-mips.cc
index afdd3b00ff515f55267de150efaefae3cfea30be..66e0a4cffb3038188b4121a9f27d85968cfaa3b5 100644
--- a/src/mips/macro-assembler-mips.cc
+++ b/src/mips/macro-assembler-mips.cc
@@ -4085,6 +4085,7 @@ void MacroAssembler::Allocate(int object_size,
                               Label* gc_required,
                               AllocationFlags flags) {
   DCHECK(object_size <= Page::kMaxRegularHeapObjectSize);
+  DCHECK((flags & ALLOCATION_FOLDED) == 0);
   if (!FLAG_inline_new) {
     if (emit_debug_code()) {
       // Trash the registers to simulate an allocation failure.
@@ -4157,7 +4158,11 @@ void MacroAssembler::Allocate(int object_size,
   // to calculate the new top.
   Addu(result_end, result, Operand(object_size));
   Branch(gc_required, Ugreater, result_end, Operand(alloc_limit));
-  sw(result_end, MemOperand(top_address));
+
+  if ((flags & ALLOCATION_FOLDING_DOMINATOR) == 0) {
+    // The top pointer is not updated for allocation folding dominators.
+    sw(result_end, MemOperand(top_address));
+  }
 
   // Tag object.
   Addu(result, result, Operand(kHeapObjectTag));
@@ -4167,6 +4172,7 @@ void MacroAssembler::Allocate(int object_size,
 void MacroAssembler::Allocate(Register object_size, Register result,
                               Register result_end, Register scratch,
                               Label* gc_required, AllocationFlags flags) {
+  DCHECK((flags & ALLOCATION_FOLDED) == 0);
   if (!FLAG_inline_new) {
     if (emit_debug_code()) {
       // Trash the registers to simulate an allocation failure.
@@ -4239,6 +4245,7 @@ void MacroAssembler::Allocate(Register object_size, Register result,
   } else {
     Addu(result_end, result, Operand(object_size));
   }
+
   Branch(gc_required, Ugreater, result_end, Operand(alloc_limit));
 
   // Update allocation top. result temporarily holds the new top.
@@ -4246,12 +4253,104 @@ void MacroAssembler::Allocate(Register object_size, Register result,
     And(alloc_limit, result_end, Operand(kObjectAlignmentMask));
     Check(eq, kUnalignedAllocationInNewSpace, alloc_limit, Operand(zero_reg));
   }
-  sw(result_end, MemOperand(top_address));
+
+  if ((flags & ALLOCATION_FOLDING_DOMINATOR) == 0) {
+    // The top pointer is not updated for allocation folding dominators.
+    sw(result_end, MemOperand(top_address));
+  }
 
   // Tag object.
   Addu(result, result, Operand(kHeapObjectTag));
 }
 
+void MacroAssembler::FastAllocate(int object_size, Register result,
+                                  Register scratch1, Register scratch2,
+                                  AllocationFlags flags) {
+  DCHECK(object_size <= Page::kMaxRegularHeapObjectSize);
+  DCHECK(!AreAliased(result, scratch1, scratch2, t9, at));
+
+  // Make object size into bytes.
+  if ((flags & SIZE_IN_WORDS) != 0) {
+    object_size *= kPointerSize;
+  }
+  DCHECK_EQ(0, object_size & kObjectAlignmentMask);
+
+  ExternalReference allocation_top =
+      AllocationUtils::GetAllocationTopReference(isolate(), flags);
+
+  // Set up allocation top address and allocation limit registers.
+  Register top_address = scratch1;
+  // This code stores a temporary value in t9.
+  Register result_end = scratch2;
+  li(top_address, Operand(allocation_top));
+  lw(result, MemOperand(top_address));
+
+  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));
+    Label aligned;
+    Branch(&aligned, eq, result_end, Operand(zero_reg));
+    li(result_end, Operand(isolate()->factory()->one_pointer_filler_map()));
+    sw(result_end, MemOperand(result));
+    Addu(result, result, Operand(kDoubleSize / 2));
+    bind(&aligned);
+  }
+
+  Addu(result_end, result, Operand(object_size));
+
+  // The top pointer is not updated for allocation folding dominators.
+  sw(result_end, MemOperand(top_address));
+
+  Addu(result, result, Operand(kHeapObjectTag));
+}
+
+void MacroAssembler::FastAllocate(Register object_size, Register result,
+                                  Register result_end, Register scratch,
+                                  AllocationFlags flags) {
+  // |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, t9, at));
+  DCHECK(!AreAliased(result_end, result, scratch, t9, at));
+  DCHECK((flags & DOUBLE_ALIGNMENT) == 0 || !object_size.is(result_end));
+
+  ExternalReference allocation_top =
+      AllocationUtils::GetAllocationTopReference(isolate(), flags);
+
+  // Set up allocation top address and allocation limit registers.
+  Register top_address = scratch;
+  // This code stores a temporary value in t9.
+  li(top_address, Operand(allocation_top));
+  lw(result, MemOperand(top_address));
+
+  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));
+    Label aligned;
+    Branch(&aligned, eq, result_end, Operand(zero_reg));
+    li(result_end, Operand(isolate()->factory()->one_pointer_filler_map()));
+    sw(result_end, MemOperand(result));
+    Addu(result, result, Operand(kDoubleSize / 2));
+    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) {
+    Lsa(result_end, result, object_size, kPointerSizeLog2);
+  } else {
+    Addu(result_end, result, Operand(object_size));
+  }
+
+  // The top pointer is not updated for allocation folding dominators.
+  sw(result_end, MemOperand(top_address));
+
+  Addu(result, result, Operand(kHeapObjectTag));
+}
 
 void MacroAssembler::AllocateTwoByteString(Register result,
                                            Register length,