Revert "Revert "Remove non-live vregs from GC map on return.""

This reverts commit 73dda0bc2adcd6a3a7d75f663a3559f8b527d485.
It also fixes the problematic line in the ReferenceMap test.

Change-Id: Ic3b62db7c040853a5ddfed589f6e0acff25d82b7
diff --git a/runtime/verifier/method_verifier.cc b/runtime/verifier/method_verifier.cc
index 2bf78d8..e182af7 100644
--- a/runtime/verifier/method_verifier.cc
+++ b/runtime/verifier/method_verifier.cc
@@ -566,8 +566,10 @@
     /* Flag instructions that are garbage collection points */
     // All invoke points are marked as "Throw" points already.
     // We are relying on this to also count all the invokes as interesting.
-    if (inst->IsBranch() || inst->IsSwitch() || inst->IsThrow() || inst->IsReturn()) {
+    if (inst->IsBranch() || inst->IsSwitch() || inst->IsThrow()) {
       insn_flags_[dex_pc].SetCompileTimeInfoPoint();
+    } else if (inst->IsReturn()) {
+      insn_flags_[dex_pc].SetCompileTimeInfoPointAndReturn();
     }
     dex_pc += inst->SizeInCodeUnits();
     inst = inst->Next();
@@ -2656,6 +2658,20 @@
       // Make workline consistent with fallthrough computed from peephole optimization.
       work_line_->CopyFromLine(fallthrough_line.get());
     }
+    if (insn_flags_[next_insn_idx].IsReturn()) {
+      // For returns we only care about the operand to the return, all other registers are dead.
+      const Instruction* ret_inst = Instruction::At(code_item_->insns_ + next_insn_idx);
+      Instruction::Code opcode = ret_inst->Opcode();
+      if ((opcode == Instruction::RETURN_VOID) || (opcode == Instruction::RETURN_VOID_BARRIER)) {
+        work_line_->MarkAllRegistersAsConflicts();
+      } else {
+        if (opcode == Instruction::RETURN_WIDE) {
+          work_line_->MarkAllRegistersAsConflictsExceptWide(ret_inst->VRegA_11x());
+        } else {
+          work_line_->MarkAllRegistersAsConflictsExcept(ret_inst->VRegA_11x());
+        }
+      }
+    }
     RegisterLine* next_line = reg_table_.GetLine(next_insn_idx);
     if (next_line != NULL) {
       // Merge registers into what we have for the next instruction,
@@ -3643,7 +3659,24 @@
      * there's nothing to "merge". Copy the registers over and mark it as changed. (This is the
      * only way a register can transition out of "unknown", so this is not just an optimization.)
      */
-    target_line->CopyFromLine(merge_line);
+    if (!insn_flags_[next_insn].IsReturn()) {
+      target_line->CopyFromLine(merge_line);
+    } else {
+      // For returns we only care about the operand to the return, all other registers are dead.
+      // Initialize them as conflicts so they don't add to GC and deoptimization information.
+      const Instruction* ret_inst = Instruction::At(code_item_->insns_ + next_insn);
+      Instruction::Code opcode = ret_inst->Opcode();
+      if ((opcode == Instruction::RETURN_VOID) || (opcode == Instruction::RETURN_VOID_BARRIER)) {
+        target_line->MarkAllRegistersAsConflicts();
+      } else {
+        target_line->CopyFromLine(merge_line);
+        if (opcode == Instruction::RETURN_WIDE) {
+          target_line->MarkAllRegistersAsConflictsExceptWide(ret_inst->VRegA_11x());
+        } else {
+          target_line->MarkAllRegistersAsConflictsExcept(ret_inst->VRegA_11x());
+        }
+      }
+    }
   } else {
     UniquePtr<RegisterLine> copy(gDebugVerify ? new RegisterLine(target_line->NumRegs(), this) : NULL);
     if (gDebugVerify) {