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[SPIR-V] Update SPV_INTEL_function_pointers extension #2254

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62 changes: 47 additions & 15 deletions sycl/doc/extensions/SPIRV/SPV_INTEL_function_pointers.asciidoc
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@ https://github.com/intel/llvm/issues
- Ben Ashbaugh, Intel
- Pawel Jurek, Intel
- Thomas Raoux, Intel
- Alex Bezzubikov, Intel

== Notice

Expand All @@ -37,7 +38,7 @@ If you are interested in using this feature in your software product, please let
[width="40%",cols="25,25"]
|==================================
| Last Modified Date | {docdate}
| Revision | G
| Revision | H
|==================================

== Dependencies
Expand Down Expand Up @@ -86,7 +87,7 @@ IndirectReferencesINTEL
Instructions added under the *FunctionPointersINTEL* capability:

----
OpFunctionPointerINTEL
OpConstFunctionPointerINTEL
OpFunctionPointerCallINTEL
----

Expand All @@ -113,7 +114,7 @@ CodeSectionINTEL
[cols="70%,30%"]
[grid="rows"]
|====
|OpFunctionPointerINTEL | 5600
|OpConstFunctionPointerINTEL| 5600
|OpFunctionPointerCallINTEL | 5601
|ReferencedIndirectlyINTEL | 5602
|FunctionPointersINTEL | 5603
Expand All @@ -133,23 +134,24 @@ Modify Section 2.2.2, Types, add the following at the end of the section: ::
[[FunctionPointer]]'Function Pointer': A pointer that results from the following
instruction:

- *OpFunctionPointerINTEL*
- *OpConstFunctionPointerINTEL*

Additionally, any *OpSelect*, *OpPhi*, *OpFunctionCall*, *OpPtrAccessChain*,
*OpLoad*, *OpAccessChain*, *OpInBoundAccessChain*, or *OpCopyObject* thas takes
a function pointer as an operand also produces a function pointer. An
*OpFunctionParameter* of pointer type is function pointer if any
*OpFunctionCall* to the function statically passes a function pointer as the
value of the parameter. *OpConstantNull* returns function pointer if 'Result
type' is function pointer.
value of the parameter. *OpCompositeExtract* and *OpConstantNull* return function pointer
if 'Result type' is function pointer.

Modify Section 2.9, Function Calling, add the following after the first sentence: ::

Functions can be called indirectly using function pointers: to do so, use
*OpFunctionPointerCallINTEL* with an operand that is the _<id>_ obtained using
*OpFunctionPointerINTEL* of the *OpFunction* to call, and the _<id>s_ of the
arguments to pass. All arguments are passed by value into the called function.
This includes pointers, through which a callee object could be modified.
*OpConstFunctionPointerINTEL* of the *OpFunction* to call,
and the _<id>s_ of the arguments to pass. All arguments are passed by value
into the called function. This includes pointers, through which a callee object
could be modified.

=== Storage Classes

Expand Down Expand Up @@ -207,16 +209,17 @@ Modify Section 3.32.6, Type-Declaration Instructions, change the third sentence
pointer type. *OpFunction* and *OpTypePointer* are only valid uses of
*OpTypeFunction*.

Modify Section 3.32.9, Function Instructions, adding to the end of the list of instructions: ::
Modify Section 3.32.7, Constant-Creation Instructions, adding to the end of the list of instructions: ::

[cols="2*1,3*3",width="100%"]
|=====
4+|[[OpFunctionPointerINTEL]]*OpFunctionPointerINTEL* +
4+|[[OpConstFunctionPointerINTEL]]*OpConstFunctionPointerINTEL* +
+
Obtains address of the specified function. +
Obtains constant address of the specified function. +
+
Result value can be used immediately in *OpFunctionPointerCallINTEL* or stored
somewhere for further usage in *OpFunctionPointerCallINTEL*. +
Result value can be used in *OpFunctionPointerCallINTEL* or inserted into
a composite constant or stored somewhere for further usage
in *OpFunctionPointerCallINTEL*. +
+
_Result Type_ must be an *OpTypePointer*. Its _Type_ operand must be the same
*OpTypeFunction* which was used as _Function Type_ operand of the _Function_
Expand All @@ -226,6 +229,8 @@ operand. Its _Storage Class_ operand must be *CodeSectionINTEL*
| 4 | 5600 | '<id>' 'Result Type' | '<id> Result ' | '<id>' 'Function'
|=====

Modify Section 3.32.9, Function Instructions, adding to the end of the list of instructions: ::

[cols="2*1,4*3",width="100%"]
|=====
5+|[[OpFunctionPointerCallINTEL]]*OpFunctionPointerCallINTEL* +
Expand All @@ -252,14 +257,17 @@ argument types must match the formal parameter types.
== Validation Rules

It is legal to use <<FunctionPointer, Function Pointer>> as 'Result Type' of
*OpFunctionArgument*, *OpUndef* and *OpConstantNULL*.
*OpFunctionArgument*, *OpCompositeExtract*, *OpUndef* and *OpConstantNULL*.

It is legal to use <<FunctionPointer, Function Pointer>> as 'Return Type' of
*OpTypeFunction*.

It is legal to use <<FunctionPointer, Function Pointer>> as 'Pointer'
argument of *OpConvertPtrToU* and as 'Result Type' of *OpConvertUToPtr*.

It is legal to use <<FunctionPointer, Function Pointer>> as 'Object'
argument of *OpCompositeInsert*.

It is illegal to use <<FunctionPointer, Function Pointer>> as 'Pointer'
argument of *OpPtrCastToGeneric*.

Expand Down Expand Up @@ -308,6 +316,28 @@ be used for ones out of the box and we don't have much use-cases for it.
*UNRESOLVED*
--

. Should we prohibit heterogenous composites with function pointers? Maybe we should
distinct <<FunctionPointer, Function Pointer>> and Constant Function Pointer?
+
--
*RESOLVED*

In general, we should not since this extension is aimed to support the whole C++ function
pointers functionality in SPIR-V.
--

. Should we distinct const and non-const function pointers in rules for *OpCompositeInsert*?
We can only use a result of *OpConstFunctionPointerINTEL* (which is a quite specific case of
<<FunctionPointer, Function Pointer>>, so we can't use the whole term in the rule)
in *OpConstantComposite*, but how should we specify that in this spec?
+
--
*RESOLVED*

Removed *OpFunctionPointerINTEL* instruction.
--


//. Issue.
//+
//--
Expand Down Expand Up @@ -336,4 +366,6 @@ be used for ones out of the box and we don't have much use-cases for it.
|F|2019-06-21|Alexey Sachkov|Added new storage class dedicated for function
pointers. Updated validation rules. Misc updates.
|G|2019-07-19|Ben Ashbaugh|Assigned SPIR-V enums, added preview extension disclaimer text.
|H|2020-07-30|Alex Bezzubikov|Replaced *OpFunctionPointerINTEL* with
*OpConstFunctionPointerINTEL*
|========================================