Record implicit null checks at the actual invoke time.

ImplicitNullChecks are recorded only for instructions directly (see NB
below) preceeded by NullChecks in the graph. This way we avoid recording
redundant safepoints and minimize the code size increase.

NB: ParallalelMoves might be inserted by the register allocator between
the NullChecks and their uses. These modify the environment and the
correct action would be to reverse their modification. This will be
addressed in a follow-up CL.

Change-Id: Ie50006e5a4bd22932dcf11348f5a655d253cd898

1 files changed, 34 insertions, 0 deletions

diff --git a/compiler/optimizing/code_generator.cc b/compiler/optimizing/code_generator.cc
index cdfd989bb8..8d9a7b71e9 100644
--- a/compiler/optimizing/code_generator.cc
+++ b/compiler/optimizing/code_generator.cc
@@ -638,6 +638,40 @@ void CodeGenerator::RecordPcInfo(HInstruction* instruction, uint32_t dex_pc) {
   }
 }
 
+bool CodeGenerator::CanMoveNullCheckToUser(HNullCheck* null_check) {
+  HInstruction* first_next_not_move = null_check->GetNextDisregardingMoves();
+  return (first_next_not_move != nullptr) && first_next_not_move->CanDoImplicitNullCheck();
+}
+
+void CodeGenerator::MaybeRecordImplicitNullCheck(HInstruction* instr) {
+  // If we are from a static path don't record the pc as we can't throw NPE.
+  // NB: having the checks here makes the code much less verbose in the arch
+  // specific code generators.
+  if (instr->IsStaticFieldSet() || instr->IsStaticFieldGet()) {
+    return;
+  }
+
+  if (!compiler_options_.GetImplicitNullChecks()) {
+    return;
+  }
+
+  if (!instr->CanDoImplicitNullCheck()) {
+    return;
+  }
+
+  // Find the first previous instruction which is not a move.
+  HInstruction* first_prev_not_move = instr->GetPreviousDisregardingMoves();
+
+  // If the instruction is a null check it means that `instr` is the first user
+  // and needs to record the pc.
+  if (first_prev_not_move != nullptr && first_prev_not_move->IsNullCheck()) {
+    HNullCheck* null_check = first_prev_not_move->AsNullCheck();
+    // TODO: The parallel moves modify the environment. Their changes need to be reverted
+    // otherwise the stack maps at the throw point will not be correct.
+    RecordPcInfo(null_check, null_check->GetDexPc());
+  }
+}
+
 void CodeGenerator::SaveLiveRegisters(LocationSummary* locations) {
   RegisterSet* register_set = locations->GetLiveRegisters();
   size_t stack_offset = first_register_slot_in_slow_path_;