Use iterators "before" the use node in HUserRecord<>.

Create a new template class IntrusiveForwardList<> that
mimicks std::forward_list<> except that all allocations
are handled externally. This is essentially the same as
boost::intrusive::slist<> but since we're not using Boost
we have to reinvent the wheel.

Use the new container to replace the HUseList and use the
iterators to "before" use nodes in HUserRecord<> to avoid
the extra pointer to the previous node which was used
exclusively for removing nodes from the list. This reduces
the size of the HUseListNode by 25%, 32B to 24B in 64-bit
compiler, 16B to 12B in 32-bit compiler. This translates
directly to overall memory savings for the 64-bit compiler
but due to rounding up of the arena allocations to 8B, we
do not get any improvement in the 32-bit compiler.

Compiling the Nexus 5 boot image with the 64-bit dex2oat
on host this CL reduces the memory used for compiling the
most hungry method, BatteryStats.dumpLocked(), by ~3.3MiB:

Before:
  MEM: used: 47829200, allocated: 48769120, lost: 939920
  Number of arenas allocated: 345,
  Number of allocations: 815492, avg size: 58
  ...
  UseListNode    13744640
  ...
After:
  MEM: used: 44393040, allocated: 45361248, lost: 968208
  Number of arenas allocated: 319,
  Number of allocations: 815492, avg size: 54
  ...
  UseListNode    10308480
  ...

Note that while we do not ship the 64-bit dex2oat to the
device, the JIT compilation for 64-bit processes is using
the 64-bit libart-compiler.

Bug: 28173563
Change-Id: I985eabd4816f845372d8aaa825a1489cf9569208

1 files changed, 2 insertions, 2 deletions

diff --git a/compiler/optimizing/pretty_printer.h b/compiler/optimizing/pretty_printer.h
index 429e6e3d3f..ee32518c01 100644
--- a/compiler/optimizing/pretty_printer.h
+++ b/compiler/optimizing/pretty_printer.h
@@ -55,13 +55,13 @@ class HPrettyPrinter : public HGraphVisitor {
     if (instruction->HasUses()) {
       PrintString(" [");
       bool first = true;
-      for (HUseIterator<HInstruction*> it(instruction->GetUses()); !it.Done(); it.Advance()) {
+      for (const HUseListNode<HInstruction*>& use : instruction->GetUses()) {
         if (first) {
           first = false;
         } else {
           PrintString(", ");
         }
-        PrintInt(it.Current()->GetUser()->GetId());
+        PrintInt(use.GetUser()->GetId());
       }
       PrintString("]");
     }