ART: Fix for no-opt debug (-O0) builds

Currently, the build process of debug builds with no optimization fails
due to missing symbol definitions.

For example, it throws errors like the following one:

ld.lld: error:
undefined symbol:
art::gc::collector::MarkSweep::MarkStackTask<false>::kMaxSize

This patch changes the missing symbols from constants to constant
expressions as a way to fix those issues. The optimized builds
get away with this issue because the values are optimized
to be inlined and not referenced.

The code at https://godbolt.org/z/3oYKoPzGj depicts similar
behaviour. Additionally, there are comments describing why
this issue occurs.

Test: ART_DEBUG_OPT_FLAG="-O0" art/tools/buildbot-build.sh --host

Change-Id: I66b5cfc885dfdfc82e3e4008b1e40fd68c19c999

5 files changed, 8 insertions, 8 deletions

diff --git a/compiler/utils/assembler.h b/compiler/utils/assembler.h
index 67f38bcbe6..4b4fb14df6 100644
--- a/compiler/utils/assembler.h
+++ b/compiler/utils/assembler.h
@@ -250,7 +250,7 @@ class AssemblerBuffer {
   // The limit is set to kMinimumGap bytes before the end of the data area.
   // This leaves enough space for the longest possible instruction and allows
   // for a single, fast space check per instruction.
-  static const int kMinimumGap = 32;
+  static constexpr int kMinimumGap = 32;
 
   ArenaAllocator* const allocator_;
   uint8_t* contents_;
diff --git a/compiler/utils/managed_register.h b/compiler/utils/managed_register.h
index 2afdc046ff..a3b33ba94d 100644
--- a/compiler/utils/managed_register.h
+++ b/compiler/utils/managed_register.h
@@ -74,7 +74,7 @@ class ManagedRegister : public ValueObject {
   explicit constexpr ManagedRegister(int reg_id) : id_(reg_id) { }
 
  protected:
-  static const int kNoRegister = -1;
+  static constexpr int kNoRegister = -1;
 
   constexpr ManagedRegister() : id_(kNoRegister) { }
 
diff --git a/runtime/class_table.h b/runtime/class_table.h
index dfae1fd9e4..0ea62456f1 100644
--- a/runtime/class_table.h
+++ b/runtime/class_table.h
@@ -98,7 +98,7 @@ class ClassTable {
 
     // Data contains the class pointer GcRoot as well as the low bits of the descriptor hash.
     mutable Atomic<uint32_t> data_;
-    static const uint32_t kHashMask = kObjectAlignment - 1;
+    static constexpr uint32_t kHashMask = kObjectAlignment - 1;
   };
 
   using DescriptorHashPair = std::pair<const char*, uint32_t>;
diff --git a/runtime/gc/allocator/rosalloc.h b/runtime/gc/allocator/rosalloc.h
index a5bfd8f5d7..9a09c88927 100644
--- a/runtime/gc/allocator/rosalloc.h
+++ b/runtime/gc/allocator/rosalloc.h
@@ -621,7 +621,7 @@ class RosAlloc {
 
   // A memory allocation request larger than this size is treated as a large object and allocated
   // at a page-granularity.
-  static const size_t kLargeSizeThreshold = 2048;
+  static constexpr size_t kLargeSizeThreshold = 2048;
 
   // If true, check that the returned memory is actually zero.
   static constexpr bool kCheckZeroMemory = kIsDebugBuild;
@@ -662,14 +662,14 @@ class RosAlloc {
   // We use thread-local runs for the size brackets whose indexes
   // are less than this index. We use shared (current) runs for the rest.
   // Sync this with the length of Thread::rosalloc_runs_.
-  static const size_t kNumThreadLocalSizeBrackets = 16;
+  static constexpr size_t kNumThreadLocalSizeBrackets = 16;
   static_assert(kNumThreadLocalSizeBrackets == kNumRosAllocThreadLocalSizeBracketsInThread,
                 "Mismatch between kNumThreadLocalSizeBrackets and "
                 "kNumRosAllocThreadLocalSizeBracketsInThread");
 
   // The size of the largest bracket we use thread-local runs for.
   // This should be equal to bracketSizes[kNumThreadLocalSizeBrackets - 1].
-  static const size_t kMaxThreadLocalBracketSize = 128;
+  static constexpr size_t kMaxThreadLocalBracketSize = 128;
 
   // We use regular (8 or 16-bytes increment) runs for the size brackets whose indexes are less than
   // this index.
@@ -677,7 +677,7 @@ class RosAlloc {
 
   // The size of the largest regular (8 or 16-byte increment) bracket. Non-regular brackets are the
   // 1 KB and the 2 KB brackets. This should be equal to bracketSizes[kNumRegularSizeBrackets - 1].
-  static const size_t kMaxRegularBracketSize = 512;
+  static constexpr size_t kMaxRegularBracketSize = 512;
 
   // The bracket size increment for the thread-local brackets (<= kMaxThreadLocalBracketSize bytes).
   static constexpr size_t kThreadLocalBracketQuantumSize = 8;
diff --git a/runtime/gc/collector/mark_sweep.cc b/runtime/gc/collector/mark_sweep.cc
index 9e5cb9c314..ebac36dc7b 100644
--- a/runtime/gc/collector/mark_sweep.cc
+++ b/runtime/gc/collector/mark_sweep.cc
@@ -688,7 +688,7 @@ class MarkSweep::MarkStackTask : public Task {
     }
   }
 
-  static const size_t kMaxSize = 1 * KB;
+  static constexpr size_t kMaxSize = 1 * KB;
 
  protected:
   class MarkObjectParallelVisitor {