Cache resolved theme values

When calling Resources#obtainStyledAttributes, if a value for an
attribute is supplied from the theme, and the value in the theme
is a reference to a resource, the reference will be resolved using
AssetManager2::ResolveReference each time the value from the theme
is selected. This causes Resources#obtainStyledAttributes to do
repeated work every time the same attribute is supplied from the
theme in multiple invocations.

Caching the result of ResolveReference reduces the cost of this
repeated work and reduces the amount of time needed to inflate views.

Before:
com.android.resources.perf (3 Tests)
[1/3] com.android.resources.perf.PerfTest#youtube: PASSED (11.748s)
    youtube_ns_median: 95490747
    youtube_ns_standardDeviation: 7282249
    youtube_ns_mean: 98442515
[2/3] com.android.resources.perf.PerfTest#maps: PASSED (10.862s)
    maps_ns_standardDeviation: 4484213
    maps_ns_mean: 87912988
    maps_ns_median: 86325549
[3/3] com.android.resources.perf.PerfTest#gmail: PASSED (24.034s)
    gmail_ns_median: 282175838
    gmail_ns_standardDeviation: 6560876
    gmail_ns_mean: 282869146

After:
com.android.resources.perf (3 Tests)
[1/3] com.android.resources.perf.PerfTest#youtube: PASSED (11.245s)
    youtube_ns_median: 92292347
    youtube_ns_standardDeviation: 5899906
    youtube_ns_mean: 93045239
[2/3] com.android.resources.perf.PerfTest#maps: PASSED (10.583s)
    maps_ns_standardDeviation: 7567929
    maps_ns_mean: 81895979
    maps_ns_median: 78647883
[3/3] com.android.resources.perf.PerfTest#gmail: PASSED (21.439s)
    gmail_ns_median: 229185043
    gmail_ns_standardDeviation: 8770133
    gmail_ns_mean: 232561234

These tests were done on a Pixel 3 and with cpu settings configured by
libs/hwui/tests/scripts/prep_generic.sh:

 Locked CPUs 4,5,6,7 to 1459200 / 2803200 KHz
 Disabled CPUs 0,1,2,3

Bug: 170232288
Test: atest ResourcesPerfWorkloads
Change-Id: I1e9e9acaa40fa60475a0e55230e11243f5b69b39

3 files changed, 36 insertions, 14 deletions

diff --git a/libs/androidfw/AssetManager2.cpp b/libs/androidfw/AssetManager2.cpp
index 3e54dc67db76..d349628c2ab4 100644
--- a/libs/androidfw/AssetManager2.cpp
+++ b/libs/androidfw/AssetManager2.cpp
@@ -963,14 +963,25 @@ base::expected<AssetManager2::SelectedValue, NullOrIOError> AssetManager2::GetRe
 }
 
 base::expected<std::monostate, NullOrIOError> AssetManager2::ResolveReference(
-    AssetManager2::SelectedValue& value) const {
+    AssetManager2::SelectedValue& value, bool cache_value) const {
   if (value.type != Res_value::TYPE_REFERENCE || value.data == 0U) {
     // Not a reference. Nothing to do.
     return {};
   }
 
-  uint32_t combined_flags = value.flags;
-  uint32_t resolve_resid = value.data;
+  const uint32_t original_flags = value.flags;
+  const uint32_t original_resid = value.data;
+  if (cache_value) {
+    auto cached_value = cached_resolved_values_.find(value.data);
+    if (cached_value != cached_resolved_values_.end()) {
+      value = cached_value->second;
+      value.flags |= original_flags;
+      return {};
+    }
+  }
+
+  uint32_t combined_flags = 0U;
+  uint32_t resolve_resid = original_resid;
   constexpr const uint32_t kMaxIterations = 20;
   for (uint32_t i = 0U;; i++) {
     auto result = GetResource(resolve_resid, true /*may_be_bag*/);
@@ -981,9 +992,15 @@ base::expected<std::monostate, NullOrIOError> AssetManager2::ResolveReference(
     if (result->type != Res_value::TYPE_REFERENCE ||
         result->data == Res_value::DATA_NULL_UNDEFINED ||
         result->data == resolve_resid || i == kMaxIterations) {
-      // This reference can't be resolved, so exit now and let the caller deal with it.
+      result->flags |= combined_flags;
+      if (cache_value) {
+        cached_resolved_values_[original_resid] = *result;
+      }
+
+      // Add the original flags after caching the result so queries with a different set of original
+      // flags do not include these original flags.
       value = *result;
-      value.flags |= combined_flags;
+      value.flags |= original_flags;
       return {};
     }
 
@@ -1353,6 +1370,8 @@ void AssetManager2::InvalidateCaches(uint32_t diff) {
       ++iter;
     }
   }
+
+  cached_resolved_values_.clear();
 }
 
 uint8_t AssetManager2::GetAssignedPackageId(const LoadedPackage* package) const {
@@ -1533,7 +1552,7 @@ base::expected<std::monostate, NullOrIOError> Theme::ResolveAttributeReference(
     return base::unexpected(std::nullopt);
   }
 
-  auto resolve_result = asset_manager_->ResolveReference(*result);
+  auto resolve_result = asset_manager_->ResolveReference(*result, true /* cache_value */);
   if (resolve_result.has_value()) {
     result->flags |= value.flags;
     value = *result;
diff --git a/libs/androidfw/AttributeResolution.cpp b/libs/androidfw/AttributeResolution.cpp
index 71919fdbb736..347b4ec8346c 100644
--- a/libs/androidfw/AttributeResolution.cpp
+++ b/libs/androidfw/AttributeResolution.cpp
@@ -39,8 +39,7 @@ class XmlAttributeFinder
     : public BackTrackingAttributeFinder<XmlAttributeFinder, size_t> {
  public:
   explicit XmlAttributeFinder(const ResXMLParser* parser)
-      : BackTrackingAttributeFinder(
-            0, parser != nullptr ? parser->getAttributeCount() : 0),
+      : BackTrackingAttributeFinder(0, parser != nullptr ? parser->getAttributeCount() : 0),
         parser_(parser) {}
 
   inline uint32_t GetAttribute(size_t index) const {
@@ -178,7 +177,7 @@ base::expected<std::monostate, IOError> ResolveAttrs(Theme* theme, uint32_t def_
         value = *attr_value;
         DEBUG_LOG("-> From theme: type=0x%x, data=0x%08x", value.type, value.data);
 
-        const auto result = assetmanager->ResolveReference(value);
+        const auto result = assetmanager->ResolveReference(value, true /* cache_value */);
         if (UNLIKELY(IsIOError(result))) {
           return base::unexpected(GetIOError(result.error()));
         }
@@ -310,7 +309,7 @@ base::expected<std::monostate, IOError> ApplyStyle(Theme* theme, ResXMLParser* x
         value = *attr_value;
         DEBUG_LOG("-> From theme: type=0x%x, data=0x%08x", value.type, value.data);
 
-        auto result = assetmanager->ResolveReference(value);
+        auto result = assetmanager->ResolveReference(value, true /* cache_value */);
         if (UNLIKELY(IsIOError(result))) {
           return base::unexpected(GetIOError(result.error()));
         }
diff --git a/libs/androidfw/include/androidfw/AssetManager2.h b/libs/androidfw/include/androidfw/AssetManager2.h
index 4e993b0838a2..a92694c94b9f 100644
--- a/libs/androidfw/include/androidfw/AssetManager2.h
+++ b/libs/androidfw/include/androidfw/AssetManager2.h
@@ -264,11 +264,14 @@ class AssetManager2 {
   // Resolves the resource referenced in `value` if the type is Res_value::TYPE_REFERENCE.
   //
   // If the data type is not Res_value::TYPE_REFERENCE, no work is done. Configuration flags of the
-  // values pointed to by the reference are OR'd into `value.flags`.
+  // values pointed to by the reference are OR'd into `value.flags`. If `cache_value` is true, then
+  // the resolved value will be cached and used when attempting to resolve the resource id specified
+  // in `value`.
   //
   // Returns a null error if the resource could not be resolved, or an I/O error if reading
   // resource data failed.
-  base::expected<std::monostate, NullOrIOError> ResolveReference(SelectedValue& value) const;
+  base::expected<std::monostate, NullOrIOError> ResolveReference(SelectedValue& value,
+                                                                 bool cache_value = false) const;
 
   // Retrieves the best matching bag/map resource with ID `resid`.
   //
@@ -446,13 +449,14 @@ class AssetManager2 {
   // a number of times for each view during View inspection.
   mutable std::unordered_map<uint32_t, std::vector<uint32_t>> cached_bag_resid_stacks_;
 
+  // Cached set of resolved resource values.
+  mutable std::unordered_map<uint32_t, SelectedValue> cached_resolved_values_;
+
   // Whether or not to save resource resolution steps
   bool resource_resolution_logging_enabled_ = false;
 
   struct Resolution {
-
     struct Step {
-
       enum class Type {
         INITIAL,
         BETTER_MATCH,