[stdlib] add overflow checks for some pointer arithmetic

- Overflow checks added for recent additions to pointer arithmetic (rounding and property pointers).
- The basic `advanced(by:)` functions will need to be dealt with separately.

Author: glessard

stdlib/public/core/UnsafePointer.swift

@@ -371,6 +371,11 @@ public struct UnsafePointer<Pointee>: _Pointer {
     to property: KeyPath<Pointee, Property>
   ) -> UnsafePointer<Property>? {
     guard let o = property._storedInlineOffset else { return nil }
+    _internalInvariant(o >= 0)
+    _debugPrecondition(
+      o == 0 || UnsafeRawPointer(self) < UnsafeRawPointer(bitPattern: 0 &- o)!,
+      "Overflow in pointer arithmetic"
+    )
     return .init(Builtin.gepRaw_Word(_rawValue, o._builtinWordValue))
   }
 
@@ -1088,6 +1093,11 @@ public struct UnsafeMutablePointer<Pointee>: _Pointer {
     to property: KeyPath<Pointee, Property>
   ) -> UnsafePointer<Property>? {
     guard let o = property._storedInlineOffset else { return nil }
+    _internalInvariant(o >= 0)
+    _debugPrecondition(
+      o == 0 || UnsafeRawPointer(self) < UnsafeRawPointer(bitPattern: 0 &- o)!,
+      "Overflow in pointer arithmetic"
+    )
     return .init(Builtin.gepRaw_Word(_rawValue, o._builtinWordValue))
   }
 
@@ -1105,6 +1115,11 @@ public struct UnsafeMutablePointer<Pointee>: _Pointer {
     to property: WritableKeyPath<Pointee, Property>
   ) -> UnsafeMutablePointer<Property>? {
     guard let o = property._storedInlineOffset else { return nil }
+    _internalInvariant(o >= 0)
+    _debugPrecondition(
+      o == 0 || UnsafeRawPointer(self) < UnsafeRawPointer(bitPattern: 0 &- o)!,
+      "Overflow in pointer arithmetic"
+    )
     return .init(Builtin.gepRaw_Word(_rawValue, o._builtinWordValue))
   }
 

stdlib/public/core/UnsafeRawPointer.swift

@@ -499,6 +499,7 @@ extension UnsafeRawPointer {
   public func alignedUp<T>(for type: T.Type) -> Self {
     let mask = UInt(Builtin.alignof(T.self)) &- 1
     let bits = (UInt(Builtin.ptrtoint_Word(_rawValue)) &+ mask) & ~mask
+    _debugPrecondition(bits != 0, "Overflow in pointer arithmetic")
     return .init(Builtin.inttoptr_Word(bits._builtinWordValue))
   }
 
@@ -515,6 +516,7 @@ extension UnsafeRawPointer {
   public func alignedDown<T>(for type: T.Type) -> Self {
     let mask = UInt(Builtin.alignof(T.self)) &- 1
     let bits = UInt(Builtin.ptrtoint_Word(_rawValue)) & ~mask
+    _debugPrecondition(bits != 0, "Overflow in pointer arithmetic")
     return .init(Builtin.inttoptr_Word(bits._builtinWordValue))
   }
 
@@ -536,6 +538,7 @@ extension UnsafeRawPointer {
       "alignment must be a whole power of 2."
     )
     let bits = (UInt(Builtin.ptrtoint_Word(_rawValue)) &+ mask) & ~mask
+    _debugPrecondition(bits != 0, "Overflow in pointer arithmetic")
     return .init(Builtin.inttoptr_Word(bits._builtinWordValue))
   }
 
@@ -557,6 +560,7 @@ extension UnsafeRawPointer {
       "alignment must be a whole power of 2."
     )
     let bits = UInt(Builtin.ptrtoint_Word(_rawValue)) & ~mask
+    _debugPrecondition(bits != 0, "Overflow in pointer arithmetic")
     return .init(Builtin.inttoptr_Word(bits._builtinWordValue))
   }
 }
@@ -1351,6 +1355,7 @@ extension UnsafeMutableRawPointer {
   public func alignedUp<T>(for type: T.Type) -> Self {
     let mask = UInt(Builtin.alignof(T.self)) &- 1
     let bits = (UInt(Builtin.ptrtoint_Word(_rawValue)) &+ mask) & ~mask
+    _debugPrecondition(bits != 0, "Overflow in pointer arithmetic")
     return .init(Builtin.inttoptr_Word(bits._builtinWordValue))
   }
 
@@ -1367,6 +1372,7 @@ extension UnsafeMutableRawPointer {
   public func alignedDown<T>(for type: T.Type) -> Self {
     let mask = UInt(Builtin.alignof(T.self)) &- 1
     let bits = UInt(Builtin.ptrtoint_Word(_rawValue)) & ~mask
+    _debugPrecondition(bits != 0, "Overflow in pointer arithmetic")
     return .init(Builtin.inttoptr_Word(bits._builtinWordValue))
   }
 
@@ -1388,6 +1394,7 @@ extension UnsafeMutableRawPointer {
       "alignment must be a whole power of 2."
     )
     let bits = (UInt(Builtin.ptrtoint_Word(_rawValue)) &+ mask) & ~mask
+    _debugPrecondition(bits != 0, "Overflow in pointer arithmetic")
     return .init(Builtin.inttoptr_Word(bits._builtinWordValue))
   }
 
@@ -1409,6 +1416,7 @@ extension UnsafeMutableRawPointer {
       "alignment must be a whole power of 2."
     )
     let bits = UInt(Builtin.ptrtoint_Word(_rawValue)) & ~mask
+    _debugPrecondition(bits != 0, "Overflow in pointer arithmetic")
     return .init(Builtin.inttoptr_Word(bits._builtinWordValue))
   }
 }