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https://github.com/carbon-language/carbon-lang.git
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Jon Ross-Perkins
61c0a8b676
This is essentially the result of looking at `.begin()` uses. We also frequently do `std::shuffle`, but unfortunately STLExtras doesn't provide a wrapper for that.
101 lines
3.3 KiB
C++
101 lines
3.3 KiB
C++
// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
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// Exceptions. See /LICENSE for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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#ifndef CARBON_COMMON_ARRAY_STACK_H_
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#define CARBON_COMMON_ARRAY_STACK_H_
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#include "common/check.h"
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#include "llvm/ADT/ArrayRef.h"
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#include "llvm/ADT/SmallVector.h"
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namespace Carbon {
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// Provides a stack of arrays. Only the array at the top of the stack can have
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// elements added.
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//
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// Example usage:
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// // Push to start.
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// PushArray();
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// // Add values.
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// AppendToTop(3);
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// // Look at values.
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// PeekArray();
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// // Pop when done.
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// PopArray();
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//
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// By using a single vector for elements, the intent is that as arrays are
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// pushed and popped, the same storage will be reused. This should yield
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// efficiencies for heap allocations. For example, in the toolchain we
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// frequently have an array per scope, and only add to the current scope's
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// array; this allows better reuse when entering and leaving scopes.
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template <typename ValueT>
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class ArrayStack {
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public:
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// Pushes a new array onto the stack.
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auto PushArray() -> void { array_offsets_.push_back(values_.size()); }
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// Pops the top array from the stack.
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auto PopArray() -> void {
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auto region = array_offsets_.pop_back_val();
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values_.truncate(region);
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}
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// Returns the top array from the stack.
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auto PeekArray() const -> llvm::ArrayRef<ValueT> {
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CARBON_CHECK(!array_offsets_.empty());
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return llvm::ArrayRef(values_).slice(array_offsets_.back());
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}
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// Returns the array at a specific index.
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auto PeekArrayAt(int index) const -> llvm::ArrayRef<ValueT> {
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auto ref = llvm::ArrayRef(values_).slice(array_offsets_[index]);
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if (index + 1 < static_cast<int>(array_offsets_.size())) {
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ref = ref.take_front(array_offsets_[index + 1] - array_offsets_[index]);
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}
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return ref;
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}
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// Returns the full set of values on the stack, regardless of whether any
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// arrays are pushed.
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auto PeekAllValues() const -> llvm::ArrayRef<ValueT> { return values_; }
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// Appends a value to the top array on the stack.
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auto AppendToTop(ValueT value) -> void {
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CARBON_CHECK(!array_offsets_.empty(),
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"Must call PushArray before AppendToTop.");
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values_.push_back(value);
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}
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// Prepends a value to the top array on the stack.
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auto PrependToTop(ValueT value) -> void {
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CARBON_CHECK(!array_offsets_.empty(),
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"Must call PushArray before PrependToTop.");
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values_.insert(values_.begin() + array_offsets_.back(), value);
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}
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// Adds multiple values to the top array on the stack.
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auto AppendToTop(llvm::ArrayRef<ValueT> values) -> void {
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CARBON_CHECK(!array_offsets_.empty(),
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"Must call PushArray before PushValues.");
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llvm::append_range(values_, values);
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}
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// Returns the current number of values in all arrays.
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auto all_values_size() const -> size_t { return values_.size(); }
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// Returns true if the stack has no arrays pushed.
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auto empty() const -> bool { return array_offsets_.empty(); }
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private:
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// For each pushed array, the start index in elements_.
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llvm::SmallVector<int32_t> array_offsets_;
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// The full set of elements in all arrays.
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llvm::SmallVector<ValueT> values_;
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};
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} // namespace Carbon
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#endif // CARBON_COMMON_ARRAY_STACK_H_
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