[PATCH] D119972: [demangler] Improve buffer hysteresis

[Nathan Sidwell via Phabricator via llvm-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
urnathan marked an inline comment as done.
Closed by commit rG024495e62660: [demangler] Improve buffer hysteresis (authored by urnathan).
Herald added a project: libc++abi.
Herald added a reviewer: libc++abi.

Changed prior to commit:
  https://reviews.llvm.org/D119972?vs=411857&id=412051#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D119972/new/

https://reviews.llvm.org/D119972

Files:
  libcxxabi/src/demangle/Utility.h
  llvm/include/llvm/Demangle/Utility.h
  llvm/unittests/Demangle/OutputBufferTest.cpp


Index: llvm/unittests/Demangle/OutputBufferTest.cpp
===================================================================
--- llvm/unittests/Demangle/OutputBufferTest.cpp
+++ llvm/unittests/Demangle/OutputBufferTest.cpp
@@ -78,3 +78,16 @@
 
   std::free(OB.getBuffer());
 }
+
+// Test when initial needed size is larger than the default.
+TEST(OutputBufferTest, Extend) {
+  OutputBuffer OB;
+
+  char Massive[2000];
+  std::memset(Massive, 'a', sizeof(Massive));
+  Massive[sizeof(Massive) - 1] = 0;
+  OB << Massive;
+  EXPECT_EQ(Massive, toString(OB));
+
+  std::free(OB.getBuffer());
+}
Index: llvm/include/llvm/Demangle/Utility.h
===================================================================
--- llvm/include/llvm/Demangle/Utility.h
+++ llvm/include/llvm/Demangle/Utility.h
@@ -37,10 +37,10 @@
   void grow(size_t N) {
     size_t Need = N + CurrentPosition;
     if (Need > BufferCapacity) {
-      // Avoid many reallocations during startup, with a bit of hysteresis.
-      constexpr size_t MinInitAlloc = 1024;
-      if (Need < MinInitAlloc)
-        Need = MinInitAlloc;
+      // Reduce the number of reallocations, with a bit of hysteresis. The
+      // number here is chosen so the first allocation will more-than-likely not
+      // allocate more than 1K.
+      Need += 1024 - 32;
       BufferCapacity *= 2;
       if (BufferCapacity < Need)
         BufferCapacity = Need;
Index: libcxxabi/src/demangle/Utility.h
===================================================================
--- libcxxabi/src/demangle/Utility.h
+++ libcxxabi/src/demangle/Utility.h
@@ -37,10 +37,10 @@
   void grow(size_t N) {
     size_t Need = N + CurrentPosition;
     if (Need > BufferCapacity) {
-      // Avoid many reallocations during startup, with a bit of hysteresis.
-      constexpr size_t MinInitAlloc = 1024;
-      if (Need < MinInitAlloc)
-        Need = MinInitAlloc;
+      // Reduce the number of reallocations, with a bit of hysteresis. The
+      // number here is chosen so the first allocation will more-than-likely not
+      // allocate more than 1K.
+      Need += 1024 - 32;
       BufferCapacity *= 2;
       if (BufferCapacity < Need)
         BufferCapacity = Need;


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