Support: Write ScaledNumbers::getRounded()

Start extracting helper functions out of -block-freq's `UnsignedFloat`
into `Support/ScaledNumber.h` with the eventual goal of moving and
renaming the class to `ScaledNumber`.

The bike shed about names is still being painted, but I'm going with
this for now.

llvm-svn: 211333

llvm/include/llvm/Analysis/BlockFrequencyInfoImpl.h

@@ -22,6 +22,7 @@
 #include "llvm/Support/BlockFrequency.h"
 #include "llvm/Support/BranchProbability.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/ScaledNumber.h"
 #include "llvm/Support/raw_ostream.h"
 #include <deque>
 #include <list>
@@ -343,12 +344,11 @@ private:
   }
 
   static UnsignedFloat getRounded(UnsignedFloat P, bool Round) {
-    if (!Round)
+    // Saturate.
+    if (P.isLargest())
       return P;
-    if (P.Digits == DigitsLimits::max())
+
-      // Careful of overflow in the exponent.
+    return ScaledNumbers::getRounded(P.Digits, P.Exponent, Round);
-      return UnsignedFloat(1, P.Exponent) <<= Width;
-    return UnsignedFloat(P.Digits + 1, P.Exponent);
   }
 };
 

llvm/include/llvm/Support/ScaledNumber.h

@@ -0,0 +1,57 @@
+//===- llvm/Support/ScaledNumber.h - Support for scaled numbers -*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file contains functions (and a class) useful for working with scaled
+// numbers -- in particular, pairs of integers where one represents digits and
+// another represents a scale.  The functions are helpers and live in the
+// namespace ScaledNumbers.  The class ScaledNumber is useful for modelling
+// certain cost metrics that need simple, integer-like semantics that are easy
+// to reason about.
+//
+// These might remind you of soft-floats.  If you want one of those, you're in
+// the wrong place.  Look at include/llvm/ADT/APFloat.h instead.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_SCALEDNUMBER_H
+#define LLVM_SUPPORT_SCALEDNUMBER_H
+
+#include <cstdint>
+#include <limits>
+#include <utility>
+
+namespace llvm {
+namespace ScaledNumbers {
+
+/// \brief Get the width of a number.
+template <class DigitsT> inline int getWidth() { return sizeof(DigitsT) * 8; }
+
+/// \brief Conditionally round up a scaled number.
+///
+/// Given \c Digits and \c Scale, round up iff \c ShouldRound is \c true.
+/// Always returns \c Scale unless there's an overflow, in which case it
+/// returns \c 1+Scale.
+///
+/// \pre adding 1 to \c Scale will not overflow INT16_MAX.
+template <class DigitsT>
+inline std::pair<DigitsT, int16_t> getRounded(DigitsT Digits, int16_t Scale,
+                                              bool ShouldRound) {
+  static_assert(!std::numeric_limits<DigitsT>::is_signed, "expected unsigned");
+
+  if (ShouldRound)
+    if (!++Digits)
+      // Overflow.
+      return std::make_pair(DigitsT(1) << (getWidth<DigitsT>() - 1), Scale + 1);
+  return std::make_pair(Digits, Scale);
+}
+}
+}
+
+#endif
+

llvm/unittests/Support/CMakeLists.txt

@@ -29,6 +29,7 @@ add_llvm_unittest(SupportTests
   ProcessTest.cpp
   ProgramTest.cpp
   RegexTest.cpp
+  ScaledNumberTest.cpp
   SourceMgrTest.cpp
   StringPool.cpp
   SwapByteOrderTest.cpp

llvm/unittests/Support/ScaledNumberTest.cpp

@@ -0,0 +1,60 @@
+//===- llvm/unittest/Support/ScaledNumberTest.cpp - ScaledPair tests -----==//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/ScaledNumber.h"
+
+#include "llvm/Support/DataTypes.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+using namespace llvm::ScaledNumbers;
+
+namespace {
+
+template <class UIntT> struct ScaledPair {
+  UIntT D;
+  int S;
+  ScaledPair(const std::pair<UIntT, int16_t> &F) : D(F.first), S(F.second) {}
+  ScaledPair(UIntT D, int S) : D(D), S(S) {}
+
+  bool operator==(const ScaledPair<UIntT> &X) const {
+    return D == X.D && S == X.S;
+  }
+};
+template <class UIntT>
+bool operator==(const std::pair<UIntT, int16_t> &L,
+                const ScaledPair<UIntT> &R) {
+  return ScaledPair<UIntT>(L) == R;
+}
+template <class UIntT>
+void PrintTo(const ScaledPair<UIntT> &F, ::std::ostream *os) {
+  *os << F.D << "*2^" << F.S;
+}
+
+typedef ScaledPair<uint32_t> SP32;
+typedef ScaledPair<uint64_t> SP64;
+
+TEST(ScaledNumberHelpersTest, getRounded) {
+  EXPECT_EQ(getRounded<uint32_t>(0, 0, false), SP32(0, 0));
+  EXPECT_EQ(getRounded<uint32_t>(0, 0, true), SP32(1, 0));
+  EXPECT_EQ(getRounded<uint32_t>(20, 21, true), SP32(21, 21));
+  EXPECT_EQ(getRounded<uint32_t>(UINT32_MAX, 0, false), SP32(UINT32_MAX, 0));
+  EXPECT_EQ(getRounded<uint32_t>(UINT32_MAX, 0, true), SP32(1 << 31, 1));
+
+  EXPECT_EQ(getRounded<uint64_t>(0, 0, false), SP64(0, 0));
+  EXPECT_EQ(getRounded<uint64_t>(0, 0, true), SP64(1, 0));
+  EXPECT_EQ(getRounded<uint64_t>(20, 21, true), SP64(21, 21));
+  EXPECT_EQ(getRounded<uint64_t>(UINT32_MAX, 0, false), SP64(UINT32_MAX, 0));
+  EXPECT_EQ(getRounded<uint64_t>(UINT32_MAX, 0, true),
+            SP64(UINT64_C(1) << 32, 0));
+  EXPECT_EQ(getRounded<uint64_t>(UINT64_MAX, 0, false), SP64(UINT64_MAX, 0));
+  EXPECT_EQ(getRounded<uint64_t>(UINT64_MAX, 0, true),
+            SP64(UINT64_C(1) << 63, 1));
+}
+}