[llvm] [IR] Require that ptrmask mask matches pointer index size (PR #69343)

[Nikita Popov via llvm-commits]

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@@ -26965,10 +26966,20 @@ to facilitate alias analysis and underlying-object detection.
 Semantics:
 """"""""""
 
-The result of ``ptrmask(ptr, mask)`` is equivalent to
-``getelementptr ptr, (ptrtoint(ptr) & mask) - ptrtoint(ptr)``. Both the returned
-pointer(s) and the first argument are based on the same underlying object (for more
-information on the *based on* terminology see
+The result of ``ptrmask(%ptr, %mask)`` is equivalent to the following expansion,
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nikic wrote:

I've added a sentence to clarify that ptrmaks only captures via the return value.

https://github.com/llvm/llvm-project/pull/69343