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, 1 insertions, 4 deletions

diff --git a/compiler/optimizing/instruction_simplifier_shared.cc b/compiler/optimizing/instruction_simplifier_shared.cc
index a11b5bd5c3..dab1ebc16d 100644
--- a/compiler/optimizing/instruction_simplifier_shared.cc
+++ b/compiler/optimizing/instruction_simplifier_shared.cc
@@ -103,13 +103,10 @@ bool TryCombineMultiplyAccumulate(HMul* mul, InstructionSet isa) {
       return false;
   }
 
-  HInstruction* use = mul->HasNonEnvironmentUses()
-      ? mul->GetUses().GetFirst()->GetUser()
-      : nullptr;
-
   ArenaAllocator* arena = mul->GetBlock()->GetGraph()->GetArena();
 
   if (mul->HasOnlyOneNonEnvironmentUse()) {
+    HInstruction* use = mul->GetUses().front().GetUser();
     if (use->IsAdd() || use->IsSub()) {
       // Replace code looking like
       //    MUL tmp, x, y