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a179bd461b4a07bf2defe91e68f1bb9edfa60551
carbon-lang/toolchain/lower/testdata/class/convert.carbon
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David BlaikieandDana Jansens a179bd461b Start plumbing through debug info type information with function parameters/return value (#6410) 
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>
2025-11-25 23:25:09 +00:00

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// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/int.carbon
//
// AUTOUPDATE
// TIP: To test this file alone, run:
// TIP: bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/class/convert.carbon
// TIP: To dump output, run:
// TIP: bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/class/convert.carbon
class IntWrapper {
var n: i32;
}
impl IntWrapper as Core.ImplicitAs(i32) {
fn Convert[self: Self]() -> i32 { return self.n; }
}
fn Consume(n: i32) {}
fn DoIt() {
var w: IntWrapper = {.n = 42};
Consume(w);
}
// CHECK:STDOUT: ; ModuleID = 'convert.carbon'
// CHECK:STDOUT: source_filename = "convert.carbon"
// CHECK:STDOUT:
// CHECK:STDOUT: @IntWrapper.val.loc24_3 = internal constant { i32 } { i32 42 }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define i32 @"_CConvert.IntWrapper.Main:ImplicitAs.Core"(ptr %self) #0 !dbg !4 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %.loc18_48.1.n = getelementptr inbounds nuw { i32 }, ptr %self, i32 0, i32 0, !dbg !11
// CHECK:STDOUT: %.loc18_48.2 = load i32, ptr %.loc18_48.1.n, align 4, !dbg !11
// CHECK:STDOUT: ret i32 %.loc18_48.2, !dbg !12
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define void @_CConsume.Main(i32 %n) #0 !dbg !13 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: ret void, !dbg !18
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define void @_CDoIt.Main() #0 !dbg !19 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %w.var = alloca { i32 }, align 8, !dbg !22
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %w.var), !dbg !22
// CHECK:STDOUT: %.loc24_31.3.n = getelementptr inbounds nuw { i32 }, ptr %w.var, i32 0, i32 0, !dbg !23
// CHECK:STDOUT: call void @llvm.memcpy.p0.p0.i64(ptr align 4 %w.var, ptr align 4 @IntWrapper.val.loc24_3, i64 4, i1 false), !dbg !22
// CHECK:STDOUT: %IntWrapper.as.ImplicitAs.impl.Convert.call = call i32 @"_CConvert.IntWrapper.Main:ImplicitAs.Core"(ptr %w.var), !dbg !24
// CHECK:STDOUT: call void @_CConsume.Main(i32 %IntWrapper.as.ImplicitAs.impl.Convert.call), !dbg !25
// CHECK:STDOUT: ret void, !dbg !26
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: readwrite)
// CHECK:STDOUT: declare void @llvm.lifetime.start.p0(ptr captures(none)) #1
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nocallback nofree nounwind willreturn memory(argmem: readwrite)
// CHECK:STDOUT: declare void @llvm.memcpy.p0.p0.i64(ptr noalias writeonly captures(none), ptr noalias readonly captures(none), i64, i1 immarg) #2
// CHECK:STDOUT:
// CHECK:STDOUT: attributes #0 = { nounwind }
// CHECK:STDOUT: attributes #1 = { nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) }
// CHECK:STDOUT: attributes #2 = { nocallback nofree nounwind willreturn memory(argmem: readwrite) }
// CHECK:STDOUT:
// CHECK:STDOUT: !llvm.module.flags = !{!0, !1}
// CHECK:STDOUT: !llvm.dbg.cu = !{!2}
// CHECK:STDOUT:
// CHECK:STDOUT: !0 = !{i32 7, !"Dwarf Version", i32 5}
// 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: "convert.carbon", directory: "")
// CHECK:STDOUT: !4 = distinct !DISubprogram(name: "Convert", linkageName: "_CConvert.IntWrapper.Main:ImplicitAs.Core", scope: null, file: !3, line: 18, type: !5, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !9)
// CHECK:STDOUT: !5 = !DISubroutineType(types: !6)
// CHECK:STDOUT: !6 = !{!7, !8}
// CHECK:STDOUT: !7 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
// CHECK:STDOUT: !8 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 8)
// CHECK:STDOUT: !9 = !{!10}
// CHECK:STDOUT: !10 = !DILocalVariable(arg: 1, scope: !4, type: !8)
// CHECK:STDOUT: !11 = !DILocation(line: 18, column: 44, scope: !4)
// CHECK:STDOUT: !12 = !DILocation(line: 18, column: 37, scope: !4)
// CHECK:STDOUT: !13 = distinct !DISubprogram(name: "Consume", linkageName: "_CConsume.Main", scope: null, file: !3, line: 21, type: !14, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !16)
// CHECK:STDOUT: !14 = !DISubroutineType(types: !15)
// CHECK:STDOUT: !15 = !{null, !7}
// CHECK:STDOUT: !16 = !{!17}
// CHECK:STDOUT: !17 = !DILocalVariable(arg: 1, scope: !13, type: !7)
// CHECK:STDOUT: !18 = !DILocation(line: 21, column: 1, scope: !13)
// CHECK:STDOUT: !19 = distinct !DISubprogram(name: "DoIt", linkageName: "_CDoIt.Main", scope: null, file: !3, line: 23, type: !20, spFlags: DISPFlagDefinition, unit: !2)
// CHECK:STDOUT: !20 = !DISubroutineType(types: !21)
// CHECK:STDOUT: !21 = !{null}
// CHECK:STDOUT: !22 = !DILocation(line: 24, column: 3, scope: !19)
// CHECK:STDOUT: !23 = !DILocation(line: 24, column: 23, scope: !19)
// CHECK:STDOUT: !24 = !DILocation(line: 25, column: 11, scope: !19)
// CHECK:STDOUT: !25 = !DILocation(line: 25, column: 3, scope: !19)
// CHECK:STDOUT: !26 = !DILocation(line: 23, column: 1, scope: !19)
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