Keep resolved String in HLoadString.

For the following reasons:
- Avoids needing to do a lookup again in CodeGenerator::EmitJitRoots.
- Fixes races where we the string was GC'ed before CodeGenerator::EmitJitRoots.
- Makes it possible to do GVN on the same string but defined in different
  dex files.

Test: test-art-host, test-art-target
Change-Id: If2b5d3079f7555427b1b96ab04546b3373fcf921
diff --git a/compiler/optimizing/code_generator_mips.cc b/compiler/optimizing/code_generator_mips.cc
index 01e0dac..9af03e8 100644
--- a/compiler/optimizing/code_generator_mips.cc
+++ b/compiler/optimizing/code_generator_mips.cc
@@ -5625,7 +5625,9 @@
   }
 }
 
-void InstructionCodeGeneratorMIPS::VisitLoadString(HLoadString* load) {
+// NO_THREAD_SAFETY_ANALYSIS as we manipulate handles whose internal object we know does not
+// move.
+void InstructionCodeGeneratorMIPS::VisitLoadString(HLoadString* load) NO_THREAD_SAFETY_ANALYSIS {
   HLoadString::LoadKind load_kind = load->GetLoadKind();
   LocationSummary* locations = load->GetLocations();
   Location out_loc = locations->Out();
@@ -5660,8 +5662,9 @@
       return;  // No dex cache slow path.
     }
     case HLoadString::LoadKind::kBootImageAddress: {
-      DCHECK_NE(load->GetAddress(), 0u);
-      uint32_t address = dchecked_integral_cast<uint32_t>(load->GetAddress());
+      uint32_t address = dchecked_integral_cast<uint32_t>(
+          reinterpret_cast<uintptr_t>(load->GetString().Get()));
+      DCHECK_NE(address, 0u);
       __ LoadLiteral(out,
                      base_or_current_method_reg,
                      codegen_->DeduplicateBootImageAddressLiteral(address));