[swift-dev] [RFC] SIL syntax for debug information Part 2: Scopes and Locations

Wed Feb 10 14:02:33 CST 2016

> On Feb 10, 2016, at 11:43 AM, Joe Groff <jgroff at apple.com> wrote:
> 
> I'm not a fan of generic metadata syntax. I think there's little enough information here that we should just print and parse it inline, something like this maybe:
> 
> debug_value %0 : $Int, let, name "k", argno 1,
>  loc "foo.swift":line:column,
>  scope @foo -> "foo.swift":parentLine:column -> "foo.swift":line:column
> 
> which I think is easier to read and test. I always have trouble mentally piecing together the DAG when updating LLVM debug info tests. If you don't think that's practical,

The main problem is that the inline information in the scopes form a tree and explicitly printing it would quickly explode. It would make ingesting the SIL complicated because we’d need to unique the scopes before building the instructions.

> I would still prefer proper declarations to metadata syntax:
> 
> debug_value <...>, scope 123, loc 456

Right, the ‘!’ prefix is redundant because the parser already knows that the next token is a scope.

> sil_scope 123 { parent_scope 124 loc 457 }

I tried to model the syntax after how SIL instructions are represented. That said, using curly braces here instead of a comma-separated list of operands is a lot more readable.

What about an even more dictionary-like syntax:

  sil_scope 123 { parent_scope: 124, loc: 457 }
  sil_scope 124 { parent_function: @func, loc: 457 }

?

> sil_loc 456 { "foo.swift":line:column }

I like this one for its compactness! Since the locations are leaf nodes, we could also inline them everywhere. The filenames might sill cause the lines to become very long, but it’s worth trying.

thanks,
adrian

> 
> -Joe
> 
>> On Feb 10, 2016, at 11:34 AM, Adrian Prantl <aprantl at apple.com> wrote:
>> 
>> Hi Everybody,
>> 
>> I’d like to solicit comments on extending the textual .sil assembler
>> language with even more debug information.
>> 
>> At the moment it is only possible to test the effects that SIL
>> optimization passes have on debug information by observing the
>> effects of a full .swift -> LLVM IR compilation. To enable us
>> writing targeted testcases for single SIL optimization passes,
>> I'd like to propose a serialization format for scope and location
>> information for textual SIL.
>> 
>> The format is inspired by LLVM IR's metadata representation, but
>> with a couple of improvements that reduce the amount of
>> individual metadata records and improve the overall readability
>> by moving the metadata definition closer to their (first) use.
>> 
>> Each SIL instruction is extended by a location and scope reference.
>> sil-instruction-def ::= (sil-value-name '=')? sil-instruction, sil-loc, sil-scope
>> sil-loc ::= 'loc' md-name
>> sil-scope ::= 'scope' md-name
>> md-name ::= '!' [0-9]+
>> 
>> The individual metadata nodes are defined in a global context, as
>> they may be shared between individual SIL functions.
>> 
>> decl ::= md-def
>> md-def ::= md-name '=' md-node
>> md-node ::= 'loc' ',' 'line' [0-9]+ ',' 'column' [0-9]+ ',' 'file' string-literal
>> md-node ::= 'scope' ',' 'loc' md-name ',' 'parent' scope-parent (',' 'inlinedCallSite' md-name )?
>> scope-parent ::= sil-function-name
>> scope-parent ::= md-name
>> 
>> Let me know what you think!
>> 
>> -- adrian
>> 
>> PS:
>> Below is an example of what this would look like in practice for the following program:
>> 
>> Swift source code
>> -----------------
>> 
>> #line 100 "abc.swift"
>> @inline(__always)
>> public func h(k : Int) -> Int { // 101
>> return k                      // 102
>> }
>> 
>> #line 200 "abc.swift"
>> @inline(__always)
>> public func g(j : Int) -> Int { // 201
>> return h(j)                   // 202
>> }
>> 
>> #line 301 "abc.swift"
>> public func f(i : Int) -> Int { // 301
>> return g(i)                   // 302
>> }
>> 
>> Verbose SIL output
>> ------------------
>> 
>> Note that metadata is defined before its first use:
>> 
>> !1 = loc, line 0, column 0
>> !2 = scope, loc !1, parent @main
>> [...]
>> !3 = loc, line 101, column 15, file "abc.swift"
>> !4 = loc, line 101, column 13, file "abc.swift"
>> !5 = scope, loc !4, parent @_TF9inlinedAt1hFSiSi
>> !6 = loc, line 102, column 3, file "abc.swift"
>> !7 = loc, line 103, column 1, file "abc.swift"
>> !8 = scope, loc !7, parent !5
>> 
>> // h(Int) -> Int
>> sil [always_inline] @_TF9inlinedAt1hFSiSi : $@convention(thin) (Int) -> Int {
>> // %0                                             // users: %1, %2
>> bb0(%0 : $Int):
>> debug_value %0 : $Int, let, name "k", argno 1, loc !3, scope !5 // id: %1 line:101:15:in_prologue
>> return %0 : $Int, loc !6, scope !8              // id: %2 line:102:3:return
>> }
>> 
>> !9 = loc, line 201, column 15, file "abc.swift"
>> !10 = loc, line 201, column 13, file "abc.swift"
>> !11 = scope, loc !10, parent @_TF9inlinedAt1gFSiSi
>> !12 = loc, line 203, column 1, file "abc.swift"
>> !13 = scope, loc !12, parent !11
>> !14 = loc, line 202, column 13, file "abc.swift"
>> !15 = scope, loc !14, parent !13
>> !16 = scope, loc !4, parent !5, inlinedCallSite !15
>> !17 = loc, line 202, column 3, file "abc.swift"
>> 
>> // g(Int) -> Int
>> sil [always_inline] @_TF9inlinedAt1gFSiSi : $@convention(thin) (Int) -> Int {
>> // %0                                             // users: %1, %2, %3
>> bb0(%0 : $Int):
>> debug_value %0 : $Int, let, name "j", argno 1, loc !9, scope !11 // id: %1 line:201:15:in_prologue
>> debug_value %0 : $Int, let, name "k", argno 1, loc !3, scope !16 // id: %2 line:101:15:in_prologue: h(Int) -> Int perf_inlined_at /Volumes/Data/swift/swift/test/DebugInfo/inlinedAt.swift:202:10
>> return %0 : $Int, loc !17, scope !13            // id: %3 line:202:3:return
>> }
>> 
>> !18 = loc, line 301, column 15, file "abc.swift"
>> !19 = loc, line 301, column 13, file "abc.swift"
>> !20 = scope, loc !19, parent @_TF9inlinedAt1fFSiSi
>> !21 = loc, line 303, column 1, file "abc.swift"
>> !22 = scope, loc !21, parent !20
>> !23 = loc, line 302, column 13, file "abc.swift"
>> !24 = scope, loc !23, parent !22
>> !25 = scope, loc !10, parent !11, inlinedCallSite !24
>> !26 = scope, loc !4, parent !16, inlinedCallSite !24
>> !27 = loc, line 302, column 3, file "abc.swift"
>> 
>> 
> 