RequirementMachine: Add a simple Histogram data structure

Author: slavapestov

lib/AST/RequirementMachine/Histogram.h

@@ -0,0 +1,150 @@
+//===--- Histogram.h - Simple histogram for statistics ----------*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2021 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/ADT/ArrayRef.h"
+
+#ifndef SWIFT_HISTOGRAM_H
+#define SWIFT_HISTOGRAM_H
+
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/raw_ostream.h"
+#include <algorithm>
+#include <vector>
+
+namespace swift {
+
+namespace rewriting {
+
+/// A simple histogram that supports two operations: recording an element, and
+/// printing a graphical representation.
+///
+/// Used by the rewrite system to record various statistics, which are dumped
+/// when the -analyze-requirement-machine frontend flag is used.
+class Histogram {
+  unsigned Size;
+  unsigned Start;
+  std::vector<unsigned> Buckets;
+  unsigned OverflowBucket;
+
+  const unsigned MaxWidth = 40;
+
+  /// This is not really the base-10 logarithm, but rather the number of digits
+  /// in \p x when printed in base 10.
+  ///
+  /// So log10(0) == 1, log10(1) == 1, log10(10) == 2, etc.
+  static unsigned log10(unsigned x) {
+    if (x == 0)
+      return 1;
+    unsigned result = 0;
+    while (x != 0) {
+      result += 1;
+      x /= 10;
+    }
+    return result;
+  }
+
+public:
+  /// Creates a histogram with \p size buckets, where the numbering begins at
+  /// \p start.
+  Histogram(unsigned size, unsigned start = 0)
+      : Size(size),
+        Start(start),
+        Buckets(size, 0),
+        OverflowBucket(0) {
+  }
+
+  /// Adds an entry to the histogram. Asserts if the \p value is smaller than
+  /// Start. The value is allowed to be greater than or equal to Start + Size,
+  /// in which case it's counted in the OverflowBucket.
+  void add(unsigned value) {
+    assert(value >= Start);
+    value -= Start;
+    if (value >= Size)
+      ++OverflowBucket;
+    else
+      ++Buckets[value];
+  }
+
+  /// Print a nice-looking graphical representation of the histogram.
+  void dump(llvm::raw_ostream &out, const StringRef labels[] = {}) {
+    unsigned sumValues = 0;
+    unsigned maxValue = 0;
+    for (unsigned i = 0; i < Size; ++i) {
+      sumValues += Buckets[i];
+      maxValue = std::max(maxValue, Buckets[i]);
+    }
+    sumValues += OverflowBucket;
+    maxValue = std::max(maxValue, OverflowBucket);
+
+    size_t maxLabelWidth = 3 + log10(Size + Start);
+    if (labels != nullptr) {
+      for (unsigned i = 0; i < Size; ++i)
+        maxLabelWidth = std::max(labels[i].size(), maxLabelWidth);
+    }
+
+    out << std::string(maxLabelWidth, ' ') << " |";
+    out << std::string(std::min(MaxWidth, maxValue), ' ');
+    out << maxValue << "\n";
+
+    out << std::string(maxLabelWidth, ' ') << " |";
+    out << std::string(std::min(MaxWidth, maxValue), ' ');
+    out << "*\n";
+
+    out << std::string(maxLabelWidth, '-') << "-+-";
+    out << std::string(std::min(MaxWidth, maxValue), '-') << "\n";
+
+    auto scaledValue = [&](unsigned value) {
+      if (maxValue > MaxWidth) {
+        if (value != 0) {
+          // If the value is non-zero, print at least one '#'.
+          return std::max(1U, (value * MaxWidth) / maxValue);
+        }
+      }
+      return value;
+    };
+
+    for (unsigned i = 0; i < Size; ++i) {
+      if (labels) {
+        out << std::string(maxLabelWidth - labels[i].size(), ' ');
+        out << labels[i];
+      } else {
+        unsigned key = i + Start;
+        out << std::string(maxLabelWidth - log10(key), ' ');
+        out << key;
+      }
+      out << " | ";
+
+      unsigned value = scaledValue(Buckets[i]);
+      out << std::string(value, '#') << "\n";
+    }
+
+    if (OverflowBucket > 0) {
+      out << ">= " << (Size + Start) << " | ";
+
+      unsigned value = scaledValue(OverflowBucket);
+      out << std::string(value, '#') << "\n";
+    }
+
+    out << std::string(maxLabelWidth, '-') << "-+-";
+    out << std::string(std::min(MaxWidth, maxValue), '-') << "\n";
+
+    out << std::string(maxLabelWidth, ' ') << " | ";
+    out << "Total: " << sumValues << "\n";
+  }
+};
+
+}  // end namespace rewriting
+
+}  // end namespace swift
+
+#endif