[llvm] 42a9c18 - [ADT] Add llvm::popcount to <bit> helper wrapper

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2022-08-23T10:36:43+01:00
New Revision: 42a9c1819cb173efb866605186c90a1ab818d46b

URL: https://github.com/llvm/llvm-project/commit/42a9c1819cb173efb866605186c90a1ab818d46b
DIFF: https://github.com/llvm/llvm-project/commit/42a9c1819cb173efb866605186c90a1ab818d46b.diff

LOG: [ADT] Add llvm::popcount to <bit> helper wrapper

This patch proposes to move the llvm::detail::PopulationCounter internal helpers into ADT/bit.h and provide a llvm::popcount implementation.

I've left the countPopulation implementation in place in MathExtras.h for now, but updated it to use llvm::popcount.

Hopefully I've got the type_traits correct - I don't use them very often.

Someday we'll move to C++20 with an actual <bit> std header, and we already have this header in place to simplify matters. We'd probably benefit from moving the other <bit> helpers here at some point, but this is a first step.

Differential Revision: https://reviews.llvm.org/D132407

Added: 
    

Modified: 
    llvm/include/llvm/ADT/bit.h
    llvm/include/llvm/Support/MathExtras.h

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/ADT/bit.h b/llvm/include/llvm/ADT/bit.h
index 8e280db1927be..f57bc6f440486 100644
--- a/llvm/include/llvm/ADT/bit.h
+++ b/llvm/include/llvm/ADT/bit.h
@@ -34,6 +34,45 @@ inline To bit_cast(const From &from) noexcept {
   return to;
 }
 
+namespace detail {
+template <typename T, std::size_t SizeOfT> struct PopulationCounter {
+  static int count(T Value) {
+    // Generic version, forward to 32 bits.
+    static_assert(SizeOfT <= 4, "Not implemented!");
+#if defined(__GNUC__)
+    return (int)__builtin_popcount(Value);
+#else
+    uint32_t v = Value;
+    v = v - ((v >> 1) & 0x55555555);
+    v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
+    return int(((v + (v >> 4) & 0xF0F0F0F) * 0x1010101) >> 24);
+#endif
+  }
+};
+
+template <typename T> struct PopulationCounter<T, 8> {
+  static int count(T Value) {
+#if defined(__GNUC__)
+    return (int)__builtin_popcountll(Value);
+#else
+    uint64_t v = Value;
+    v = v - ((v >> 1) & 0x5555555555555555ULL);
+    v = (v & 0x3333333333333333ULL) + ((v >> 2) & 0x3333333333333333ULL);
+    v = (v + (v >> 4)) & 0x0F0F0F0F0F0F0F0FULL;
+    return int((uint64_t)(v * 0x0101010101010101ULL) >> 56);
+#endif
+  }
+};
+} // namespace detail
+
+/// Count the number of set bits in a value.
+/// Ex. popcount(0xF000F000) = 8
+/// Returns 0 if the word is zero.
+template <typename T, typename = std::enable_if_t<std::is_unsigned_v<T>>>
+inline int popcount(T Value) noexcept {
+  return detail::PopulationCounter<T, sizeof(T)>::count(Value);
+}
+
 } // namespace llvm
 
 #endif

diff  --git a/llvm/include/llvm/Support/MathExtras.h b/llvm/include/llvm/Support/MathExtras.h
index a396e69997870..bade1e41d089e 100644
--- a/llvm/include/llvm/Support/MathExtras.h
+++ b/llvm/include/llvm/Support/MathExtras.h
@@ -13,6 +13,7 @@
 #ifndef LLVM_SUPPORT_MATHEXTRAS_H
 #define LLVM_SUPPORT_MATHEXTRAS_H
 
+#include "llvm/ADT/bit.h"
 #include "llvm/Support/Compiler.h"
 #include <cassert>
 #include <climits>
@@ -525,37 +526,6 @@ unsigned countTrailingOnes(T Value, ZeroBehavior ZB = ZB_Width) {
   return countTrailingZeros<T>(~Value, ZB);
 }
 
-namespace detail {
-template <typename T, std::size_t SizeOfT> struct PopulationCounter {
-  static unsigned count(T Value) {
-    // Generic version, forward to 32 bits.
-    static_assert(SizeOfT <= 4, "Not implemented!");
-#if defined(__GNUC__)
-    return __builtin_popcount(Value);
-#else
-    uint32_t v = Value;
-    v = v - ((v >> 1) & 0x55555555);
-    v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
-    return ((v + (v >> 4) & 0xF0F0F0F) * 0x1010101) >> 24;
-#endif
-  }
-};
-
-template <typename T> struct PopulationCounter<T, 8> {
-  static unsigned count(T Value) {
-#if defined(__GNUC__)
-    return __builtin_popcountll(Value);
-#else
-    uint64_t v = Value;
-    v = v - ((v >> 1) & 0x5555555555555555ULL);
-    v = (v & 0x3333333333333333ULL) + ((v >> 2) & 0x3333333333333333ULL);
-    v = (v + (v >> 4)) & 0x0F0F0F0F0F0F0F0FULL;
-    return unsigned((uint64_t)(v * 0x0101010101010101ULL) >> 56);
-#endif
-  }
-};
-} // namespace detail
-
 /// Count the number of set bits in a value.
 /// Ex. countPopulation(0xF000F000) = 8
 /// Returns 0 if the word is zero.
@@ -564,7 +534,7 @@ inline unsigned countPopulation(T Value) {
   static_assert(std::numeric_limits<T>::is_integer &&
                     !std::numeric_limits<T>::is_signed,
                 "Only unsigned integral types are allowed.");
-  return detail::PopulationCounter<T, sizeof(T)>::count(Value);
+  return (unsigned)llvm::popcount(Value);
 }
 
 /// Return true if the argument contains a non-empty sequence of ones with the