[llvm] [LangRef] Add a description of the semantics of call signatures. (PR #136189)

[Nikita Popov via llvm-commits]

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@@ -9475,10 +9475,11 @@ This instruction requires several arguments:
    from the :ref:`datalayout string<langref_datalayout>` will be used.
 #. '``ty``': the type of the call instruction itself which is also the
    type of the return value. Functions that return no value are marked
-   ``void``.
+   ``void``. The signature is computed based on the return type and argument
+   types.
 #. '``fnty``': shall be the signature of the function being invoked. The
-   argument types must match the types implied by this signature. This
-   type can be omitted if the function is not varargs.
+   argument types must match the types implied by this signature. Thisa
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nikic wrote:

```suggestion
   argument types must match the types implied by this signature. This
```

https://github.com/llvm/llvm-project/pull/136189