[llvm] [ADT] Simplify PointerBitMask in PointerIntPair.h (NFC) (PR #158210)

[Jakub Kuderski via llvm-commits]

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@@ -173,8 +173,7 @@ struct PointerIntPairInfo {
                 "PointerIntPair with integer size too large for pointer");
   enum MaskAndShiftConstants : uintptr_t {
     /// PointerBitMask - The bits that come from the pointer.
-    PointerBitMask =
-        ~(uintptr_t)(((intptr_t)1 << PtrTraits::NumLowBitsAvailable) - 1),
+    PointerBitMask = ((uintptr_t)-1) << PtrTraits::NumLowBitsAvailable,
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kuhar wrote:

I think it's more common to do `~(uintptr_t(0))` for all ones? Something like `numeric_limits` would be ideal, but I don't remember if there's a helper for all ones.

https://github.com/llvm/llvm-project/pull/158210