Generate Nops to ensure that debug stack maps have distinct PC.

Change-Id: I5740ec958a20d236634b66df0e675382ed5c16fc
diff --git a/compiler/optimizing/code_generator_mips64.cc b/compiler/optimizing/code_generator_mips64.cc
index 05834ff..e334100 100644
--- a/compiler/optimizing/code_generator_mips64.cc
+++ b/compiler/optimizing/code_generator_mips64.cc
@@ -2750,6 +2750,10 @@
 }
 
 void InstructionCodeGeneratorMIPS64::VisitNativeDebugInfo(HNativeDebugInfo* info) {
+  if (codegen_->HasStackMapAtCurrentPc()) {
+    // Ensure that we do not collide with the stack map of the previous instruction.
+    __ Nop();
+  }
   codegen_->RecordPcInfo(info, info->GetDexPc());
 }