Yeah, option 1 seems reasonable to me. I might give it attribute-like spelling,
though, to help bracket it and keep it separate from the real name and
declaration:
sil [debug_decl_context test.foo : <T> (T) -> ()] @_Tfoo : $... {
}
-Joe
> On Dec 15, 2015, at 4:30 PM, Adrian Prantl <[email protected]> wrote:
>
>>
>> On Dec 15, 2015, at 2:37 PM, Joe Groff <[email protected]> wrote:
>>
>>>
>>> On Dec 15, 2015, at 2:34 PM, Adrian Prantl <[email protected]> wrote:
>>>
>>>>
>>>> On Dec 15, 2015, at 2:27 PM, Joe Groff <[email protected]> wrote:
>>>>
>>>>>
>>>>> On Dec 15, 2015, at 1:25 PM, Adrian Prantl <[email protected]> wrote:
>>>>>
>>>>>>
>>>>>> On Dec 10, 2015, at 10:19 AM, John McCall <[email protected]> wrote:
>>>>>>
>>>>>>> On Dec 10, 2015, at 8:31 AM, Joe Groff via swift-dev
>>>>>>> <[email protected]> wrote:
>>>>>>>> On Dec 9, 2015, at 4:15 PM, Adrian Prantl via swift-dev
>>>>>>>> <[email protected]> wrote:
>>>>>>>>
>>>>>>>> In order to write textual SIL -> SIL testcases that exercise the
>>>>>>>> handling of debug information by SIL passes, we need to make a couple
>>>>>>>> of additions to the textual SIL language. In memory, the debug
>>>>>>>> information attached to SIL instructions references information from
>>>>>>>> the AST. If we want to create debug info from parsing a textual .sil
>>>>>>>> file, these bits need to be made explicit.
>>>>>>>>
>>>>>>>> Let me illustrate this with an example. The function
>>>>>>>>
>>>>>>>>> func foo(x : Int) -> Int {
>>>>>>>>> return bar(x)
>>>>>>>>> }
>>>>>>>>
>>>>>>>> is compiled to SIL as
>>>>>>>>
>>>>>>>>> // main.foo (Swift.Int) -> Swift.Int
>>>>>>>>> sil hidden @_TF4main3fooFSiSi : $@convention(thin) (Int) -> Int {
>>>>>>>>> // %0 // users: %1, %2, %4
>>>>>>>>> bb0(%0 : $Int):
>>>>>>>>> debug_value %0 : $Int // let x, argno: 1 // id: %1
>>>>>>>>> line:1:10:in_prologue
>>>>>>>>> return %4 : $Int // id: %5
>>>>>>>>> line:2:3:return
>>>>>>>>> }
>>>>>>>>
>>>>>>>> Note that there is a bunch of information available in comments that
>>>>>>>> will be lost once we parse that textual SIL again. I’d like to add
>>>>>>>> syntax to SIL for the information in the comments. This proposal deals
>>>>>>>> with lifting the debug variable information (the first comment) into
>>>>>>>> actual SIL syntax. A similar proposal for locations will be coming
>>>>>>>> soon.
>>>>>>>> With the proposed syntax, this could like like:
>>>>>>>>
>>>>>>>>> sil hidden @_TF4main3fooFSiSi : $@convention(thin) (Int) -> Int {
>>>>>>>>> bb0(%0 : $Int):
>>>>>>>>> debug_value %0 : $Int, !dbg_var(name: "x", type: "_TTSi", argno: 1)
>>>>>>>>> return %4 : $Int
>>>>>>>>> }
>>>>>>>>
>>>>>>>> More formally, debug variable info may be attached to debug_value,
>>>>>>>> debug_value_addr, alloc_box, and alloc_stack instructions.
>>>>>>>>
>>>>>>>> sil-instruction ::= 'alloc_stack' sil-type dbg-var
>>>>>>>> sil-instruction ::= 'alloc_stack' sil-type dbg-var
>>>>>>>> sil-instruction ::= debug_value sil-operand dbg-var
>>>>>>>> sil-instruction ::= debug_value_addr sil-operand dbg-var
>>>>>>>> dbg-var ::= ‘!dbg_var’ ‘(‘ var-attr (',' var-attr)*) ‘)'
>>>>>>>> var-attr ::= ‘name:’ string-literal
>>>>>>>> var-attr ::= ’type:’ string-literal
>>>>>>>> var-attr ::= ‘argno:’ integer-literal
>>>>>>>>
>>>>>>>> This syntax for `dbg-var` is borrowed straight from LLVM IR and thus
>>>>>>>> invokes a familiar feeling. Since the primary use-case of it will be
>>>>>>>> in test cases, the verbose dictionary-like syntax is really helpful.
>>>>>>>>
>>>>>>>> Syntax alternatives I’ve considered and rejected include:
>>>>>>>> 1. debug_value %0 : $Int, “x”, “_TtSi”, 1
>>>>>>>> Why: Hard to read, potentially ambiguous because some fields are
>>>>>>>> optional.
>>>>>>>>
>>>>>>>> 2. debug_value [name “x”] [type “_TtSi”] [argno 1] %0 : $Int
>>>>>>>> Why: Attributes in square brackets don’t typically have arguments and
>>>>>>>> come before the entity they are modifying.
>>>>>>>>
>>>>>>>> 3. debug_value @var(name: “x”, type: “_TtSi”, argno: 1) %0 : $Int
>>>>>>>> Why: The ‘@‘ sigil is used not just for attributes but also for global
>>>>>>>> symbols and thus creates an ambiguity.
>>>>>>>
>>>>>>> Thanks for working on this, Adrian! My thoughts:
>>>>>>>
>>>>>>> - I don't see a reason to mangle the type name at SIL time. You should
>>>>>>> reference the formal AST type directly in the instruction, and print
>>>>>>> and parse it using the normal (Swift) type parser.
>>>>>>
>>>>>> In addition to all the other good reasons to do this, this means that
>>>>>> archetypes in the type will be (1) sensibly bound in the context and (2)
>>>>>> actually substituted by inlining and generic specialization.
>>>>>
>>>>> By deferring the type mangling to IRGen time I’m hitting an interesting
>>>>> problem:
>>>>>
>>>>> Let’s say we have the function
>>>>> func id<T>(x : T) -> T { return x }
>>>>>
>>>>> which is translated to SIL as
>>>>>
>>>>>> func id<T>(x: T) -> T // FuncDecl
>>>>>>
>>>>>> // declcontext.id <A> (A) -> A
>>>>>> sil hidden @_TF11declcontext2idurFxx : $@convention(thin) <T> (@out T,
>>>>>> @in T) -> () {
>>>>>> bb0(%0 : $*T, %1 : $*T):
>>>>>> debug_value_addr %1 : $*T, let, name "x", argno 1
>>>>>> copy_addr [take] %1 to [initialization] %0 : $*T
>>>>>> %4 = tuple ()
>>>>>> return %4 : $()
>>>>>> }
>>>>>
>>>>> When emitting debug info for “x” we need to determine the mangled name of
>>>>> “T”. Since T is an archetype, the Mangler needs its DeclContext. In a
>>>>> compilation from source the DeclContext is readily available and the
>>>>> FuncDecl itself.
>>>>> However, when parsing this from SIL it is unclear how to match up the
>>>>> SILFunction with the FuncDecl to establish the DeclContext for the
>>>>> Mangler. It would be possible to demangle the SILFunction’s name and then
>>>>> look up the FuncDecl by name in the SwiftModule and then filter the
>>>>> lookup results by type. But this filtering would not work after function
>>>>> signature optimizations.
>>>>> Another option is to explicitly call out the DeclContext by adding a
>>>>> sil-decl-ref attribute, like this:
>>>>>
>>>>>> debug_value_addr %1 : $*T, let, name "x", argno 1, declctx #id!1
>>>>>
>>>>>
>>>>> But it looks like sil-decl-refs also aren’t expressive enough to
>>>>> distinguish between foo() / foo(x:Int) / foo<T>(x:T).
>>>>>
>>>>> Am I missing something obvious?
>>>>>
>>>>
>>>> Don't SILFunctions already reference a context ValueDecl for debug
>>>> purposes?
>>>
>>> If you’re refering to SILFunction::getDeclContext() this field is only
>>> populated by the regular SILGen path. ParseSIL does not (yet) do this. I
>>> ran into the above problem while trying to set the DeclContext of
>>> SILFunctions that are created by ParseSIL.cpp.
>>
>> We could add some syntax to the sil function syntax to reference the debug
>> DeclContext. I wouldn't try to demangle the name to guess what it's supposed
>> to be.
>>
>
> Here are a couple of horrible ideas how this could be done:
>
>
> 1. Extend sil-decl-ref to allow specifying a type:
> Grammar:
> sil-function ::= 'sil' sil-linkage? sil-function-name ':' sil-type
> ‘declcontext’ sil-decl-ref
> '{' sil-basic-block+ '}'
> Example:
>
> // Decl
> func foo<T>(i : Int) -> T
>
> // SIL function + DeclContextRef
> sil @_TF4test3foo... : $@convention(thin) <T> (@out T, @in T) -> ()
> declcontext test.foo$<T>(Int) -> (T) {
>
> 2. Extend ValueDecls in .sil files with a unique id
> Example:
>
> // Decl + ID
> func foo() #1
>
> // SIL function + DeclContextRef
> sil @_TF4test3foo... : $... declcontext #1 {
>
> 3. Extend ValueDecls with a unique id that happens to be its mangled/silgen
> name
> Example:
>
> // Decl + ID
> @_silgen_name("@_TF4test3foo...”) func foo()
> // SIL function + DeclContextRef
> sil @_TF4test3foo... : $... declcontext @_TF4test3foo... {
>
> I personally lean towards something along the lines of option 1. What do you
> think?
>
> -- adrian
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