[llvm] [ADT] Refactor Bitset to Be More Constexpr-Usable and Add More Member Functions (PR #172062)

[Jiachen Yuan via llvm-commits]

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@@ -96,14 +109,28 @@ class Bitset {
 
   constexpr size_t size() const { return NumBits; }
 
-  bool any() const {
-    return llvm::any_of(Bits, [](BitWord I) { return I != 0; });
+  constexpr bool any() const {
+    for (unsigned I = 0; I < NumWords - 1; ++I)
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JiachenYuan wrote:

Previously, the last word needed some special masking due to the messy situation when the size of the `Bitset` is not a multiple of the `BitwordBits`. However, as I refactored to maintain the "Remainder bits are always 0" invariant, the speical handling of the last word in these functions is not needed anymore. So, in short, there is no -1 anymore.

The summary of the latest commit: https://github.com/llvm/llvm-project/pull/172062#issuecomment-3657243363

https://github.com/llvm/llvm-project/pull/172062