Subzero: Improve the behavior of resizing vectors.

src/IceUtils.h

Index: src/IceUtils.h
diff --git a/src/IceUtils.h b/src/IceUtils.h
index 83b3fe9116e4638fe57292d0d600249f66d0ac00..2c7c62b44a226e6a7e435ae735dee677e684bf29 100644
--- a/src/IceUtils.h
+++ b/src/IceUtils.h
@@ -36,14 +36,14 @@ template <typename D, typename S> inline D bitCopy(const S &Source) {
 }
 
 /// Check whether an N-bit two's-complement representation can hold value.
-template <typename T> static inline bool IsInt(int N, T value) {
+template <typename T> inline bool IsInt(int N, T value) {
   assert((0 < N) &&
          (static_cast<unsigned int>(N) < (CHAR_BIT * sizeof(value))));
   T limit = static_cast<T>(1) << (N - 1);
   return (-limit <= value) && (value < limit);
 }
 
-template <typename T> static inline bool IsUint(int N, T value) {
+template <typename T> inline bool IsUint(int N, T value) {
   assert((0 < N) &&
          (static_cast<unsigned int>(N) < (CHAR_BIT * sizeof(value))));
   T limit = static_cast<T>(1) << N;
@@ -52,7 +52,7 @@ template <typename T> static inline bool IsUint(int N, T value) {
 
 /// Check whether the magnitude of value fits in N bits, i.e., whether an
 /// (N+1)-bit sign-magnitude representation can hold value.
-template <typename T> static inline bool IsAbsoluteUint(int N, T Value) {
+template <typename T> inline bool IsAbsoluteUint(int N, T Value) {
   assert((0 < N) &&
          (static_cast<unsigned int>(N) < (CHAR_BIT * sizeof(Value))));
   if (Value < 0)
@@ -62,14 +62,14 @@ template <typename T> static inline bool IsAbsoluteUint(int N, T Value) {
 
 /// Return true if the addition X + Y will cause integer overflow for integers
 /// of type T.
-template <typename T> static inline bool WouldOverflowAdd(T X, T Y) {
+template <typename T> inline bool WouldOverflowAdd(T X, T Y) {
   return ((X > 0 && Y > 0 && (X > std::numeric_limits<T>::max() - Y)) ||
           (X < 0 && Y < 0 && (X < std::numeric_limits<T>::min() - Y)));
 }
 
 /// Adds x to y and stores the result in sum. Returns true if the addition
 /// overflowed.
-static inline bool add_overflow(uint32_t x, uint32_t y, uint32_t *sum) {
+inline bool add_overflow(uint32_t x, uint32_t y, uint32_t *sum) {
   static_assert(std::is_same<uint32_t, unsigned>::value, "Must match type");
 #if __has_builtin(__builtin_uadd_overflow)
   return __builtin_uadd_overflow(x, y, sum);
@@ -80,20 +80,20 @@ static inline bool add_overflow(uint32_t x, uint32_t y, uint32_t *sum) {
 }
 
 /// Return true if X is already aligned by N, where N is a power of 2.
-template <typename T> static inline bool IsAligned(T X, intptr_t N) {
+template <typename T> inline bool IsAligned(T X, intptr_t N) {
   assert(llvm::isPowerOf2_64(N));
   return (X & (N - 1)) == 0;
 }
 
 /// Return Value adjusted to the next highest multiple of Alignment.
-static inline uint32_t applyAlignment(uint32_t Value, uint32_t Alignment) {
+inline uint32_t applyAlignment(uint32_t Value, uint32_t Alignment) {
   assert(llvm::isPowerOf2_32(Alignment));
   return (Value + Alignment - 1) & -Alignment;
 }
 
 /// Return amount which must be added to adjust Pos to the next highest
 /// multiple of Align.
-static inline uint64_t OffsetToAlignment(uint64_t Pos, uint64_t Align) {
+inline uint64_t OffsetToAlignment(uint64_t Pos, uint64_t Align) {
   assert(llvm::isPowerOf2_64(Align));
   uint64_t Mod = Pos & (Align - 1);
   if (Mod == 0)
@@ -103,26 +103,53 @@ static inline uint64_t OffsetToAlignment(uint64_t Pos, uint64_t Align) {
 
 /// Rotate the value bit pattern to the left by shift bits.
 /// Precondition: 0 <= shift < 32
-static inline uint32_t rotateLeft32(uint32_t value, uint32_t shift) {
+inline uint32_t rotateLeft32(uint32_t value, uint32_t shift) {
   if (shift == 0)
     return value;
   return (value << shift) | (value >> (32 - shift));
 }
 
 /// Rotate the value bit pattern to the right by shift bits.
-static inline uint32_t rotateRight32(uint32_t value, uint32_t shift) {
+inline uint32_t rotateRight32(uint32_t value, uint32_t shift) {
   if (shift == 0)
     return value;
   return (value >> shift) | (value << (32 - shift));
 }
 
 /// Returns true if Val is +0.0. It requires T to be a floating point type.
-template <typename T> static bool isPositiveZero(T Val) {
+template <typename T> bool isPositiveZero(T Val) {
   static_assert(std::is_floating_point<T>::value,
                 "Input type must be floating point");
   return Val == 0 && !std::signbit(Val);
 }
 
+/// Resize a vector (or other suitable container) to a particular size, and also
+/// reserve possibly a larger size to avoid repeatedly recopying as the
+/// container grows.  It uses a strategy of doubling capacity up to a certain
+/// point, after which it bumps the capacity by a fixed amount.
+template <typename Container>
+inline void reserveAndResize(Container &V, uint32_t Size,
+                             uint32_t ChunkSizeBits = 10) {
+#if __has_builtin(__builtin_clz)
+  // Don't call reserve() if Size==0.
+  if (Size > 0) {
+    uint32_t Mask;
+    if (Size <= (1 << ChunkSizeBits)) {
+      // For smaller sizes, reserve the smallest power of 2 greater than or
+      // equal to Size.
+      Mask =
+          ((1 << (CHAR_BIT * sizeof(uint32_t) - __builtin_clz(Size))) - 1) - 1;
+    } else {
+      // For larger sizes, round up to the smallest multiple of 1<<ChunkSizeBits
+      // greater than or equal to Size.
+      Mask = (1 << ChunkSizeBits) - 1;
+    }
+    V.reserve((Size + Mask) & ~Mask);
+  }
+#endif
+  V.resize(Size);
+}
+
 /// An RAII class to ensure that a boolean flag is restored to its previous
 /// value upon function exit.
 ///