[scudo] Add static vector functionality.

[JoshuaMBa]

The scudo vector implementation maintains static local data before
switching to dynamically allocated data as the array size grows.
Users of the vector must now specify the size of the static local data
through the vector template (the default size has been removed).
If 0 is specified for the size of the static local data, an assertion will
be triggered.

[llvmbot]

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: Joshua Baehring (JoshuaMBa)

Changes

The scudo vector implementation maintains static local data before
switching to dynamically allocated data as the array size grows.
Users of the vector can now specify the size of the static local data
through the vector template (the default size is currently set to
10 * sizeof(T) where T is the vector element type).

---

Full diff: https://github.com/llvm/llvm-project/pull/98986.diff

1 Files Affected:

• (modified) compiler-rt/lib/scudo/standalone/vector.h (+9-6)

diff --git a/compiler-rt/lib/scudo/standalone/vector.h b/compiler-rt/lib/scudo/standalone/vector.h
index ca10cc281d770..d972ef068bee5 100644
--- a/compiler-rt/lib/scudo/standalone/vector.h
+++ b/compiler-rt/lib/scudo/standalone/vector.h
@@ -9,6 +9,7 @@
 #ifndef SCUDO_VECTOR_H_
 #define SCUDO_VECTOR_H_
 
+#include "common.h"
 #include "mem_map.h"
 
 #include <string.h>
@@ -21,7 +22,7 @@ namespace scudo {
 // implementation supports only POD types.
 //
 // NOTE: This class is not meant to be used directly, use Vector<T> instead.
-template <typename T> class VectorNoCtor {
+template <typename T, size_t StaticCapacity> class VectorNoCtor {
 public:
   T &operator[](uptr I) {
     DCHECK_LT(I, Size);
@@ -116,18 +117,19 @@ template <typename T> class VectorNoCtor {
   uptr CapacityBytes = 0;
   uptr Size = 0;
 
-  T LocalData[256 / sizeof(T)] = {};
+  T LocalData[StaticCapacity] = {};
   MemMapT ExternalBuffer;
 };
 
-template <typename T> class Vector : public VectorNoCtor<T> {
+template <typename T, size_t StaticCapacity = 10>
+class Vector : public VectorNoCtor<T, Max<size_t>(10, StaticCapacity)> {
 public:
-  constexpr Vector() { VectorNoCtor<T>::init(); }
+  constexpr Vector() { VectorNoCtor<T, StaticCapacity>::init(); }
   explicit Vector(uptr Count) {
-    VectorNoCtor<T>::init(Count);
+    VectorNoCtor<T, StaticCapacity>::init(Count);
     this->resize(Count);
   }
-  ~Vector() { VectorNoCtor<T>::destroy(); }
+  ~Vector() { VectorNoCtor<T, StaticCapacity>::destroy(); }
   // Disallow copies and moves.
   Vector(const Vector &) = delete;
   Vector &operator=(const Vector &) = delete;
@@ -138,3 +140,4 @@ template <typename T> class Vector : public VectorNoCtor<T> {
 } // namespace scudo
 
 #endif // SCUDO_VECTOR_H_
+

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[cferris1000]

Originally, I though we might want to allow a zero length capacity. But thinking about it a bit more, I don't think we should since that would likely be a bug. If we ever decide to allow it, we can change the static assert.

Chia-hung, make sure the usage of bytes instead of items is okay with you.

[ChiaHungDuan]

Originally, I though we might want to allow a zero length capacity. But thinking about it a bit more, I don't think we should since that would likely be a bug. If we ever decide to allow it, we can change the static assert.

Chia-hung, make sure the usage of bytes instead of items is okay with you.

Left a comment about the default size.

About the zero length, I told Jushua that he can either do default to 1 if it's 0 (like what llvm::SmallVector does) or static_assert that. Based on your suggestion, I think it's better to just disallow it.