Support stackalloc expressions anywhere for C# 8.

standard/expressions.md

@@ -3176,8 +3176,7 @@ The safe context rules for a stack allocation expression are described in [§16.
 ```ANTLR
 stackalloc_expression
     : 'stackalloc' unmanaged_type '[' expression ']'
-    | 'stackalloc' unmanaged_type? '[' constant_expression? ']'
-      stackalloc_initializer
+    | 'stackalloc' unmanaged_type? '[' constant_expression? ']' stackalloc_initializer
     ;
 
 stackalloc_initializer
@@ -3207,14 +3206,12 @@ When a *stackalloc_initializer* is present:
 
 Each *stackalloc_element_initializer* shall have an implicit conversion to *unmanaged_type* ([§10.2](conversions.md#102-implicit-conversions)). The *stackalloc_element_initializer*s initialize elements in the allocated memory in increasing order, starting with the element at index zero. In the absence of a *stackalloc_initializer*, the content of the newly allocated memory is undefined.
 
-The result of a *stackalloc_expression* is an instance of type `Span<T>`, where `T` is the *unmanaged_type*:
+If a *stackalloc_expression* occurs directly as the initializing expression of a *local_variable_declaration* ([§13.6.2](statements.md#1362-local-variable-declarations)), where the *local_variable_type* is either a pointer type ([§23.3](unsafe-code.md#233-pointer-types)) or inferred (`var`), then the result of the *stackalloc_expression* is a pointer of type `T *` ([§23.9](????)). In this case the *stackalloc_expression* must appear in unsafe code. Otherwise the result of a *stackalloc_expression* is an instance of type `Span<T>`, where `T` is the *unmanaged_type*:
 
 - `Span<T>` ([§C.3](standard-library.md#c3-standard-library-types-not-defined-in-isoiec-23271)) is a ref struct type ([§16.2.3](structs.md#1623-ref-modifier)), which presents a block of memory, here the block allocated by the *stackalloc_expression*, as an indexable collection of typed (`T`) items.
 - The result’s `Length` property returns the number of items allocated.
 - The result’s indexer ([§15.9](classes.md#159-indexers)) returns a *variable_reference* ([§9.5](variables.md#95-variable-references)) to an item of the allocated block and is range checked.
 
-> *Note*: When occurring in unsafe code the result of a *stackalloc_expression* may be of a different type, see ([§23.9](unsafe-code.md#239-stack-allocation)). *end note*
-
 Stack allocation initializers are not permitted in `catch` or `finally` blocks ([§13.11](statements.md#1311-the-try-statement)).
 
 > *Note*: There is no way to explicitly free memory allocated using `stackalloc`. *end note*

standard/unsafe-code.md

@@ -1051,9 +1051,7 @@ When the outermost containing struct variable of a fixed-size buffer member is a
 
 See [§12.8.22](expressions.md#12822-stack-allocation) for general information about the operator `stackalloc`. Here, the ability of that operator to result in a pointer is discussed.
 
-In an unsafe context if a *stackalloc_expression* ([§12.8.22](expressions.md#12822-stack-allocation)) occurs as the initializing expression of a *local_variable_declaration* ([§13.6.2](statements.md#1362-local-variable-declarations)), where the *local_variable_type* is either a pointer type ([§23.3](unsafe-code.md#233-pointer-types)) or inferred (`var`), then the result of the *stackalloc_expression* is a pointer of type `T *` to be beginning of the allocated block, where `T` is the *unmanaged_type* of the *stackalloc_expression*.
-
-In all other respects the semantics of *local_variable_declaration*s ([§13.6.2](statements.md#1362-local-variable-declarations)) and *stackalloc_expression*s ([§12.8.22](expressions.md#12822-stack-allocation)) in unsafe contexts follow those defined for safe contexts.
+When a *stackalloc_expression* occurs as the initializing expression of a *local_variable_declaration* ([§13.6.2](statements.md#1362-local-variable-declarations)), where the *local_variable_type* is either a pointer type ([§23.3](unsafe-code.md#233-pointer-types)) or inferred (`var`), the result of the *stackalloc_expression* is a pointer of type `T *`, where `T` is the *unmanaged_type* of the *stackalloc_expression*. In this case the result is a pointer to be beginning of the allocated block.
 
 > *Example*:
 >