[PATCH] D135119: [scudo] Optimize scudo test string allocation

[Dominic Chen via Phabricator via llvm-commits]

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When the underlying vector becomes full, it resizes, remaps, and then copies over the old data. To avoid thes excess allocations, allow selection of the backing vector size from the string constructor.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D135119

Files:
  compiler-rt/lib/scudo/standalone/string_utils.h
  compiler-rt/lib/scudo/standalone/tests/strings_test.cpp


Index: compiler-rt/lib/scudo/standalone/tests/strings_test.cpp
===================================================================
--- compiler-rt/lib/scudo/standalone/tests/strings_test.cpp
+++ compiler-rt/lib/scudo/standalone/tests/strings_test.cpp
@@ -43,9 +43,10 @@
 }
 
 TEST(ScudoStringsTest, ClearLarge) {
-  scudo::ScopedString Str;
+  const char appendString[] = "123";
+  scudo::ScopedString Str(sizeof(appendString) * 10000);
   for (int i = 0; i < 10000; ++i)
-    Str.append("123");
+    Str.append(appendString);
   Str.clear();
   EXPECT_EQ(0ul, Str.length());
   EXPECT_EQ('\0', *Str.data());
@@ -75,7 +76,7 @@
   // Use a ScopedString that spans a page, and attempt to write past the end
   // of it with variations of append. The expectation is for nothing to crash.
   const scudo::uptr PageSize = scudo::getPageSizeCached();
-  scudo::ScopedString Str;
+  scudo::ScopedString Str(2 * PageSize);
   Str.clear();
   fillString(Str, 2 * PageSize);
   Str.clear();
Index: compiler-rt/lib/scudo/standalone/string_utils.h
===================================================================
--- compiler-rt/lib/scudo/standalone/string_utils.h
+++ compiler-rt/lib/scudo/standalone/string_utils.h
@@ -18,7 +18,11 @@
 
 class ScopedString {
 public:
-  explicit ScopedString() { String.push_back('\0'); }
+  explicit ScopedString() { init(); }
+  explicit ScopedString(uptr Size) {
+    String.reserve(Size + 1);
+    init();
+  }
   uptr length() { return String.size() - 1; }
   const char *data() { return String.data(); }
   void clear() {
@@ -30,6 +34,7 @@
   void output() const { outputRaw(String.data()); }
 
 private:
+  void init() { String.push_back('\0'); }
   Vector<char> String;
 };
 


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