Merge a number of assertion failure fixes to the 3.0 branch.

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
===================================================================
--- src/x64/macro-assembler-x64.cc	(revision 6703)
+++ src/x64/macro-assembler-x64.cc	(working copy)
@@ -1539,6 +1539,18 @@
 }
 
 
+void MacroAssembler::Ret(int bytes_dropped, Register scratch) {
+  if (is_uint16(bytes_dropped)) {
+    ret(bytes_dropped);
+  } else {
+    pop(scratch);
+    addq(rsp, Immediate(bytes_dropped));
+    push(scratch);
+    ret(0);
+  }
+}
+
+
 void MacroAssembler::FCmp() {
   fucomip();
   fstp(0);
@@ -2096,11 +2108,11 @@
 
   Register top_reg = result_end.is_valid() ? result_end : result;
 
-  if (top_reg.is(result)) {
-    addq(top_reg, Immediate(object_size));
-  } else {
-    lea(top_reg, Operand(result, object_size));
+  if (!top_reg.is(result)) {
+    movq(top_reg, result);
   }
+  addq(top_reg, Immediate(object_size));
+  j(carry, gc_required);
   movq(kScratchRegister, new_space_allocation_limit);
   cmpq(top_reg, Operand(kScratchRegister, 0));
   j(above, gc_required);
@@ -2150,7 +2162,12 @@
   // Calculate new top and bail out if new space is exhausted.
   ExternalReference new_space_allocation_limit =
       ExternalReference::new_space_allocation_limit_address();
-  lea(result_end, Operand(result, element_count, element_size, header_size));
+
+  // We assume that element_count*element_size + header_size does not
+  // overflow.
+  lea(result_end, Operand(element_count, element_size, header_size));
+  addq(result_end, result);
+  j(carry, gc_required);
   movq(kScratchRegister, new_space_allocation_limit);
   cmpq(result_end, Operand(kScratchRegister, 0));
   j(above, gc_required);
@@ -2196,6 +2213,7 @@
     movq(result_end, object_size);
   }
   addq(result_end, result);
+  j(carry, gc_required);
   movq(kScratchRegister, new_space_allocation_limit);
   cmpq(result_end, Operand(kScratchRegister, 0));
   j(above, gc_required);