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Start plumbing through debug info type information with function parameters/return value (#6410)

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This adds just enough debug info for i32/int parameters and return
values, with a path forward for adding DWARF type metadata for other
types.

As it happens, return type information is carried separately from
parameter information:
* Return type information is carried in the `type` of the `DISubprogram`
  (as a `DISubroutineType` - which does carry parameter type information
  as well, but that's unused when the DWARF is emitted by LLVM)
* Parameter information is carried by `DILocalVariable`s with a non-zero
  `arg` value (representing the order of function parameters)

In the absence of locations for the parameters (future work), nothing
would usually keep the `DILocalVariable` live/reachable when emitting
DWARF - so for cases where this can happen (for clang, this happens in
optimized builds where all references to the parameter variable might be
optimized away) the variables can be "retained" in a list on the
`DISubprogram` - achieved by passing `AlwaysPreserve` parameter to
`createParameterVariable` (adds them to a list, then that list gets
attached to the `DISubprogram` when it's finalized later)

For now, any unsupported types are emitted as `void*` (except void
return, which is implemented as void) as a placeholder.

Given this example:
```
import Core library "io";
class MyClass {
}
fn Unsupported(v: MyClass) {
}
fn Ret() -> i32 {
  return 42;
}
fn Arg(x: i32) {
  Core.Print(x);
}
fn Run() {
}
```
this is the resulting DWARF:
```
DW_TAG_compile_unit
  DW_AT_name    ("test.carbon")
  DW_TAG_subprogram
    DW_AT_name  ("Unsupported")
    DW_TAG_formal_parameter
      DW_AT_type        (0x00000066 "void *")
  DW_TAG_subprogram
    DW_AT_name  ("Ret")
    DW_AT_type  (0x00000062 "int")
  DW_TAG_subprogram
    DW_AT_name  ("Arg")
    DW_TAG_formal_parameter
      DW_AT_type        (0x00000062 "int")
  DW_TAG_subprogram
    DW_AT_name  ("Run")
  DW_TAG_base_type
    DW_AT_name  ("int")
  DW_TAG_pointer_type
```
And the debugger:
```
(gdb) p Ret()
$1 = 42
(gdb) p Arg(4)
4
$2 = void
```

I'm not sure if there's a way this logic should be merged with the logic
for making the `llvm::Function` type (which the `DISubroutineType`
building code was inspired by/copied from) - since they're done at
different times/places, I don't think there's an easy way to do it in
one pass, but maybe the code can be shared (even if it's run twice) in
some generic `SemIR::Function` type walker.

---------

Co-authored-by: Dana Jansens <danakj@orodu.net>
This commit is contained in:
David Blaikie
2025-11-25 23:25:09 +00:00
committed by GitHub
co-authored by Dana Jansens
parent 0baa74d96f
commit a179bd461b
184 changed files with 8098 additions and 6049 deletions
Download Patch File Download Diff File Expand all files Collapse all files
toolchain/lower/testdata/function/call/tuple_param.carbon
Vendored
+16 -10
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@@ -24,14 +24,14 @@ fn Main() {
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define void @_CF.Main({ i32 } %b, ptr %c) #0 !dbg !4 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: ret void, !dbg !7
// CHECK:STDOUT: ret void, !dbg !11
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define void @_CMain.Main() #0 !dbg !8 {
// CHECK:STDOUT: define void @_CMain.Main() #0 !dbg !12 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: call void @_CF.Main({ i32 } { i32 1 }, ptr @tuple.11a.loc16_20.6), !dbg !9
// CHECK:STDOUT: ret void, !dbg !10
// CHECK:STDOUT: call void @_CF.Main({ i32 } { i32 1 }, ptr @tuple.11a.loc16_20.6), !dbg !15
// CHECK:STDOUT: ret void, !dbg !16
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: attributes #0 = { nounwind }
@@ -43,10 +43,16 @@ fn Main() {
// CHECK:STDOUT: !1 = !{i32 2, !"Debug Info Version", i32 3}
// CHECK:STDOUT: !2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
// CHECK:STDOUT: !3 = !DIFile(filename: "tuple_param.carbon", directory: "")
// CHECK:STDOUT: !4 = distinct !DISubprogram(name: "F", linkageName: "_CF.Main", scope: null, file: !3, line: 13, type: !5, spFlags: DISPFlagDefinition, unit: !2)
// CHECK:STDOUT: !4 = distinct !DISubprogram(name: "F", linkageName: "_CF.Main", scope: null, file: !3, line: 13, type: !5, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !8)
// CHECK:STDOUT: !5 = !DISubroutineType(types: !6)
// CHECK:STDOUT: !6 = !{}
// CHECK:STDOUT: !7 = !DILocation(line: 13, column: 1, scope: !4)
// CHECK:STDOUT: !8 = distinct !DISubprogram(name: "Main", linkageName: "_CMain.Main", scope: null, file: !3, line: 15, type: !5, spFlags: DISPFlagDefinition, unit: !2)
// CHECK:STDOUT: !9 = !DILocation(line: 16, column: 3, scope: !8)
// CHECK:STDOUT: !10 = !DILocation(line: 15, column: 1, scope: !8)
// CHECK:STDOUT: !6 = !{null, !7, !7}
// CHECK:STDOUT: !7 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 8)
// CHECK:STDOUT: !8 = !{!9, !10}
// CHECK:STDOUT: !9 = !DILocalVariable(arg: 1, scope: !4, type: !7)
// CHECK:STDOUT: !10 = !DILocalVariable(arg: 2, scope: !4, type: !7)
// CHECK:STDOUT: !11 = !DILocation(line: 13, column: 1, scope: !4)
// CHECK:STDOUT: !12 = distinct !DISubprogram(name: "Main", linkageName: "_CMain.Main", scope: null, file: !3, line: 15, type: !13, spFlags: DISPFlagDefinition, unit: !2)
// CHECK:STDOUT: !13 = !DISubroutineType(types: !14)
// CHECK:STDOUT: !14 = !{null}
// CHECK:STDOUT: !15 = !DILocation(line: 16, column: 3, scope: !12)
// CHECK:STDOUT: !16 = !DILocation(line: 15, column: 1, scope: !12)