SuperSize: Caspian: Use symbol PSS instead of size

This prevents double-counting the size contribution of symbols
with aliases: rather than each of N aliases having size S, they
will each have PSS S/N.

Bug: 1011921
Change-Id: I3add28981d543a5b56dd2e77f1bbeb3ee44ddd17
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1891141
Commit-Queue: Jasper Chapman-Black <jaspercb@chromium.org>
Reviewed-by: Samuel Huang <huangs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710996}

tools/binary_size/libsupersize/caspian/caspian_web.cc

@@ -48,7 +48,7 @@ void BuildTree(bool group_by_component,
 
   if (minimum_size_bytes > 0) {
     filters.push_back([minimum_size_bytes](const Symbol& sym) -> bool {
-      return sym.size >= minimum_size_bytes;
+      return sym.pss() >= minimum_size_bytes;
     });
   }
 

tools/binary_size/libsupersize/caspian/model.cc

@@ -99,7 +99,7 @@ NodeStats::~NodeStats() = default;
 NodeStats::NodeStats(SectionId sectionId,
                      int32_t count,
                      int32_t highlight,
-                     int32_t size) {
+                     float size) {
   child_stats[sectionId] = {count, highlight, size};
 }
 
@@ -124,7 +124,7 @@ NodeStats& NodeStats::operator+=(const NodeStats& other) {
 
 SectionId NodeStats::ComputeBiggestSection() const {
   SectionId ret = SectionId::kNone;
-  int32_t max = 0;
+  float max = 0.0f;
   for (auto& pair : child_stats) {
     if (pair.second.size > max) {
       ret = pair.first;

tools/binary_size/libsupersize/caspian/model.h

@@ -44,6 +44,11 @@ struct Symbol {
   Symbol();
   Symbol(const Symbol& other);
 
+  float pss() const {
+    int alias_count = aliases ? aliases->size() : 1;
+    return static_cast<float>(size) / alias_count;
+  }
+
   int32_t address = 0;
   int32_t size = 0;
   int32_t flags = 0;
@@ -81,7 +86,7 @@ struct SizeInfo {
 struct Stat {
   int32_t count = 0;
   int32_t highlight = 0;
-  int32_t size = 0;
+  float size = 0.0f;
 
   void operator+=(const Stat& other) {
     count += other.count;
@@ -93,7 +98,7 @@ struct Stat {
 struct NodeStats {
   NodeStats();
   ~NodeStats();
-  NodeStats(SectionId section, int32_t count, int32_t highlight, int32_t size);
+  NodeStats(SectionId section, int32_t count, int32_t highlight, float size);
   void WriteIntoJson(Json::Value* out) const;
   NodeStats& operator+=(const NodeStats& other);
   SectionId ComputeBiggestSection() const;
@@ -109,7 +114,7 @@ struct TreeNode {
   std::string_view id_path;
   const char* src_path = nullptr;
   const char* component = nullptr;
-  int32_t size = 0;
+  float size = 0.0f;
   NodeStats node_stats;
   int32_t flags = 0;
   int32_t short_name_index = 0;

tools/binary_size/libsupersize/caspian/tree_builder.cc

@@ -123,9 +123,10 @@ void TreeBuilder::AddFileEntry(const std::string_view source_path,
     TreeNode* symbol_node = new TreeNode();
     symbol_node->container_type = ContainerType::kSymbol;
     symbol_node->id_path = sym->full_name;
-    symbol_node->size = sym->size;
-    symbol_node->node_stats = NodeStats(
-        size_info_->ShortSectionName(sym->section_name), 1, 0, sym->size);
+    symbol_node->size = sym->pss();
+    symbol_node->node_stats =
+        NodeStats(size_info_->ShortSectionName(sym->section_name), 1, 0,
+                  symbol_node->size);
     AttachToParent(symbol_node, file_node);
   }