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Fix description of pointer in ldloca.s #11314

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Fix description of pointer in ldloca.s #11314

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2 changes: 1 addition & 1 deletion xml/System.Reflection.Emit/OpCodes.xml
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Expand Up @@ -10423,7 +10423,7 @@ The following <xref:System.Reflection.Emit.ILGenerator.Emit%2A> method overloads

1. The address stored in the local variable at the specified index is pushed onto the stack.

The `ldloca.s` instruction pushes the address of the local variable number at the passed index onto the stack, where local variables are numbered 0 onwards. The value pushed on the stack is already aligned correctly for use with instructions like <xref:System.Reflection.Emit.OpCodes.Ldind_I> and <xref:System.Reflection.Emit.OpCodes.Stind_I>. The result is a transient pointer (type `*`).
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I'm concerned that I don't have a plausible story for how this kind of mistake could have been made, so I'm not enormously confident that this is a mistake. But on main the docs are not internally consistent between ldloca and ldloca.s.

The spec appears to be ambiguous. It contains two usages of the term "transient pointer":

Instructions that create pointers which are guaranteed not to point into the memory manager’s heaps (e.g., ldloca, ldarga, and ldsflda) produce transient pointers (type *) that can be used wherever a managed pointer (type &) or unmanaged pointer (type native unsigned int) is expected.

and

*, a “transient pointer,” which can be used only within the body of a single method, that points to a value known to be in unmanaged memory (see the CIL Instruction Set specification for more details. * types are generated internally within the CLI; they are not created by the user).

But then the spec for ldloca is explicit:

The result is a managed pointer (type &).

So really I don't know what the correct resolution is, or even what the semantics are.

The `ldloca.s` instruction pushes the address of the local variable number at the passed index onto the stack, where local variables are numbered 0 onwards. The value pushed on the stack is already aligned correctly for use with instructions like <xref:System.Reflection.Emit.OpCodes.Ldind_I> and <xref:System.Reflection.Emit.OpCodes.Stind_I>. The result is a managed pointer (type `&`).

The `ldloca.s` instruction provides an efficient encoding for use with the local variables 0 through 255.

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