creating workflow for mirror::String compression

All-ASCII String characters are stored in 8-bit blocks
instead of 16-bit. The compression has not taken place, but all
workflow are in the code already (changing kUseStringCompression in
string.h file to TRUE will enable the feature)

Notes: Feature works on interpreter only without optimizing

Test art: m ART_TEST_INTERPRETER=true ART_TEST_OPTIMIZING=false
          test-art-host

Also tested with String tests from libcore/:
1. libcore.java.lang.StringTest
2. libcore.java.lang.StringBufferTest
3. libcore.java.lang.StringBuilderTest
4. libcore.java.lang.OldStringTest
5. libcore.java.lang.OldStringBufferTest

Memory improvement is 33% (from 6.03% to 4.03%, total String memory
from all apps per total memory of all apps) measured on Angler
with Hprof tools

Bug: 31040547
Change-Id: I9cc92c265ebf1305fc06b5fc33efd83797660cce

1 files changed, 1 insertions, 1 deletions

diff --git a/runtime/interpreter/interpreter_common.h b/runtime/interpreter/interpreter_common.h
index 90c8227443..acdc270b28 100644
--- a/runtime/interpreter/interpreter_common.h
+++ b/runtime/interpreter/interpreter_common.h
@@ -450,7 +450,7 @@ static inline void TraceExecution(const ShadowFrame& shadow_frame, const Instruc
       oss << StringPrintf(" vreg%u=0x%08X", i, raw_value);
       if (ref_value != nullptr) {
         if (ref_value->GetClass()->IsStringClass() &&
-            ref_value->AsString()->GetValue() != nullptr) {
+            !ref_value->AsString()->IsValueNull()) {
           oss << "/java.lang.String \"" << ref_value->AsString()->ToModifiedUtf8() << "\"";
         } else {
           oss << "/" << PrettyTypeOf(ref_value);