Remove unnecessary indirection from MemMap.

Avoid plain MemMap pointers being passed around by changing
the MemMap to moveable and return MemMap objects by value.
Previously we could have a valid zero-size MemMap but this
is now forbidden.

MemMap::RemapAtEnd() is changed to avoid the explicit call
to munmap(); mmap() with MAP_FIXED automatically removes
old mappings for overlapping regions.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Test: Pixel 2 XL boots.
Test: m test-art-target-gtest
Test: testrunner.py --target --optimizing
Change-Id: I12bd453c26a396edc20eb141bfd4dad20923f170

3 files changed, 12 insertions, 11 deletions

diff --git a/compiler/common_compiler_test.cc b/compiler/common_compiler_test.cc
index 87197becf9..2f017662e2 100644
--- a/compiler/common_compiler_test.cc
+++ b/compiler/common_compiler_test.cc
@@ -221,7 +221,7 @@ void CommonCompilerTest::TearDown() {
   callbacks_.reset();
   verification_results_.reset();
   compiler_options_.reset();
-  image_reservation_.reset();
+  image_reservation_.Reset();
 
   CommonRuntimeTest::TearDown();
 }
@@ -323,18 +323,18 @@ void CommonCompilerTest::ReserveImageSpace() {
   // accidentally end up colliding with the fixed memory address when we need to load the image.
   std::string error_msg;
   MemMap::Init();
-  image_reservation_.reset(MemMap::MapAnonymous("image reservation",
-                                                reinterpret_cast<uint8_t*>(ART_BASE_ADDRESS),
-                                                (size_t)120 * 1024 * 1024,  // 120MB
-                                                PROT_NONE,
-                                                false /* no need for 4gb flag with fixed mmap*/,
-                                                false /* not reusing existing reservation */,
-                                                &error_msg));
-  CHECK(image_reservation_.get() != nullptr) << error_msg;
+  image_reservation_ = MemMap::MapAnonymous("image reservation",
+                                            reinterpret_cast<uint8_t*>(ART_BASE_ADDRESS),
+                                            (size_t)120 * 1024 * 1024,  // 120MB
+                                            PROT_NONE,
+                                            false /* no need for 4gb flag with fixed mmap */,
+                                            false /* not reusing existing reservation */,
+                                            &error_msg);
+  CHECK(image_reservation_.IsValid()) << error_msg;
 }
 
 void CommonCompilerTest::UnreserveImageSpace() {
-  image_reservation_.reset();
+  image_reservation_.Reset();
 }
 
 void CommonCompilerTest::SetDexFilesForOatFile(const std::vector<const DexFile*>& dex_files) {
diff --git a/compiler/common_compiler_test.h b/compiler/common_compiler_test.h
index db38110400..366489c58f 100644
--- a/compiler/common_compiler_test.h
+++ b/compiler/common_compiler_test.h
@@ -115,7 +115,7 @@ class CommonCompilerTest : public CommonRuntimeTest {
   std::unique_ptr<CompilerDriver> compiler_driver_;
 
  private:
-  std::unique_ptr<MemMap> image_reservation_;
+  MemMap image_reservation_;
 
   // Chunks must not move their storage after being created - use the node-based std::list.
   std::list<std::vector<uint8_t>> header_code_and_maps_chunks_;
diff --git a/compiler/utils/swap_space.cc b/compiler/utils/swap_space.cc
index 1f9ad4242d..dee83d1c71 100644
--- a/compiler/utils/swap_space.cc
+++ b/compiler/utils/swap_space.cc
@@ -141,6 +141,7 @@ void* SwapSpace::Alloc(size_t size) {
           it->size -= size;
         } else {
           // Changing in place would break the std::set<> ordering, we need to remove and insert.
+          // TODO: When C++17 becomes available, use std::map<>::extract(), modify, insert.
           free_by_size_.erase(it);
           free_by_size_.insert(new_value);
         }