Swap Boost.Container's small_vector out for LLVM's

This implementation misses a shrink to fit function, but reassigning the
vector with a fresh one should be equivalent.

src/include/llvm/small-vector.cpp

@@ -0,0 +1,163 @@
+//===- llvm/ADT/SmallVector.cpp - 'Normally small' vectors ----------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the SmallVector class.
+//
+//===----------------------------------------------------------------------===//
+
+// Taken from
+// https://github.com/llvm/llvm-project/blob/f14334ffa1191ad734d2a994609cf8220c5b7abf/llvm/lib/Support/SmallVector.cpp
+
+#include "small-vector.h"
+
+#define LLVM_ENABLE_EXCEPTIONS
+
+#include <cstdint>
+#ifdef LLVM_ENABLE_EXCEPTIONS
+#include <stdexcept>
+#endif
+using namespace llvm;
+
+// Check that no bytes are wasted and everything is well-aligned.
+namespace {
+// These structures may cause binary compat warnings on AIX. Suppress the
+// warning since we are only using these types for the static assertions below.
+#if defined(_AIX)
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Waix-compat"
+#endif
+struct Struct16B {
+    alignas(16) void* X;
+};
+struct Struct32B {
+    alignas(32) void* X;
+};
+#if defined(_AIX)
+#pragma GCC diagnostic pop
+#endif
+}  // namespace
+static_assert(sizeof(SmallVector<void*, 0>) ==
+                  sizeof(unsigned) * 2 + sizeof(void*),
+              "wasted space in SmallVector size 0");
+static_assert(alignof(SmallVector<Struct16B, 0>) >= alignof(Struct16B),
+              "wrong alignment for 16-byte aligned T");
+static_assert(alignof(SmallVector<Struct32B, 0>) >= alignof(Struct32B),
+              "wrong alignment for 32-byte aligned T");
+static_assert(sizeof(SmallVector<Struct16B, 0>) >= alignof(Struct16B),
+              "missing padding for 16-byte aligned T");
+static_assert(sizeof(SmallVector<Struct32B, 0>) >= alignof(Struct32B),
+              "missing padding for 32-byte aligned T");
+static_assert(sizeof(SmallVector<void*, 1>) ==
+                  sizeof(unsigned) * 2 + sizeof(void*) * 2,
+              "wasted space in SmallVector size 1");
+
+static_assert(sizeof(SmallVector<char, 0>) == sizeof(void*) * 2 + sizeof(void*),
+              "1 byte elements have word-sized type for size and capacity");
+
+/// Report that MinSize doesn't fit into this vector's size type. Throws
+/// std::length_error or calls report_fatal_error.
+[[noreturn]] static void report_size_overflow(size_t MinSize, size_t MaxSize);
+static void report_size_overflow(size_t MinSize, size_t MaxSize) {
+    std::string Reason = "SmallVector unable to grow. Requested capacity (" +
+                         std::to_string(MinSize) +
+                         ") is larger than maximum value for size type (" +
+                         std::to_string(MaxSize) + ")";
+#ifdef LLVM_ENABLE_EXCEPTIONS
+    throw std::length_error(Reason);
+#else
+    report_fatal_error(Twine(Reason));
+#endif
+}
+
+/// Report that this vector is already at maximum capacity. Throws
+/// std::length_error or calls report_fatal_error.
+[[noreturn]] static void report_at_maximum_capacity(size_t MaxSize);
+static void report_at_maximum_capacity(size_t MaxSize) {
+    std::string Reason =
+        "SmallVector capacity unable to grow. Already at maximum size " +
+        std::to_string(MaxSize);
+#ifdef LLVM_ENABLE_EXCEPTIONS
+    throw std::length_error(Reason);
+#else
+    report_fatal_error(Twine(Reason));
+#endif
+}
+
+// Note: Moving this function into the header may cause performance regression.
+template <class Size_T>
+static size_t getNewCapacity(size_t MinSize,
+                             size_t /*TSize*/,
+                             size_t OldCapacity) {
+    constexpr size_t MaxSize = std::numeric_limits<Size_T>::max();
+
+    // Ensure we can fit the new capacity.
+    // This is only going to be applicable when the capacity is 32 bit.
+    if (MinSize > MaxSize)
+        report_size_overflow(MinSize, MaxSize);
+
+    // Ensure we can meet the guarantee of space for at least one more element.
+    // The above check alone will not catch the case where grow is called with a
+    // default MinSize of 0, but the current capacity cannot be increased.
+    // This is only going to be applicable when the capacity is 32 bit.
+    if (OldCapacity == MaxSize)
+        report_at_maximum_capacity(MaxSize);
+
+    // In theory 2*capacity can overflow if the capacity is 64 bit, but the
+    // original capacity would never be large enough for this to be a problem.
+    size_t NewCapacity = 2 * OldCapacity + 1;  // Always grow.
+    return std::min(std::max(NewCapacity, MinSize), MaxSize);
+}
+
+// Note: Moving this function into the header may cause performance regression.
+template <class Size_T>
+void* SmallVectorBase<Size_T>::mallocForGrow(size_t MinSize,
+                                             size_t TSize,
+                                             size_t& NewCapacity) {
+    NewCapacity = getNewCapacity<Size_T>(MinSize, TSize, this->capacity());
+    // return llvm::safe_malloc(NewCapacity * TSize);
+    return malloc(NewCapacity * TSize);
+}
+
+// Note: Moving this function into the header may cause performance regression.
+template <class Size_T>
+void SmallVectorBase<Size_T>::grow_pod(void* FirstEl,
+                                       size_t MinSize,
+                                       size_t TSize) {
+    size_t NewCapacity =
+        getNewCapacity<Size_T>(MinSize, TSize, this->capacity());
+    void* NewElts;
+    if (BeginX == FirstEl) {
+        NewElts = malloc(NewCapacity * TSize);
+
+        // Copy the elements over.  No need to run dtors on PODs.
+        memcpy(NewElts, this->BeginX, size() * TSize);
+    } else {
+        // If this wasn't grown from the inline copy, grow the allocated space.
+        NewElts = realloc(this->BeginX, NewCapacity * TSize);
+    }
+
+    this->BeginX = NewElts;
+    this->Capacity = NewCapacity;
+}
+
+template class llvm::SmallVectorBase<uint32_t>;
+
+// Disable the uint64_t instantiation for 32-bit builds.
+// Both uint32_t and uint64_t instantiations are needed for 64-bit builds.
+// This instantiation will never be used in 32-bit builds, and will cause
+// warnings when sizeof(Size_T) > sizeof(size_t).
+#if SIZE_MAX > UINT32_MAX
+template class llvm::SmallVectorBase<uint64_t>;
+
+// Assertions to ensure this #if stays in sync with SmallVectorSizeType.
+static_assert(sizeof(SmallVectorSizeType<char>) == sizeof(uint64_t),
+              "Expected SmallVectorBase<uint64_t> variant to be in use.");
+#else
+static_assert(sizeof(SmallVectorSizeType<char>) == sizeof(uint32_t),
+              "Expected SmallVectorBase<uint32_t> variant to be in use.");
+#endif