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a179bd461b4a07bf2defe91e68f1bb9edfa60551
carbon-lang/toolchain/lower/testdata/index/array_element_access.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/index/array_element_access.carbon
// TIP: To dump output, run:
// TIP: bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/index/array_element_access.carbon
fn A() -> (i32, i32) { return (1, 2); }
fn B() -> array(i32, 2) { return (1, 2); }
fn Run() {
var a: array(i32, 2) = A();
var b: i32 = 1;
var c: i32 = a[b];
var d: i32 = B()[1];
}
// CHECK:STDOUT: ; ModuleID = 'array_element_access.carbon'
// CHECK:STDOUT: source_filename = "array_element_access.carbon"
// CHECK:STDOUT:
// CHECK:STDOUT: @tuple.21c.loc12_37 = internal constant { i32, i32 } { i32 1, i32 2 }
// CHECK:STDOUT: @array.loc14_40 = internal constant [2 x i32] [i32 1, i32 2]
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define void @_CA.Main(ptr sret({ i32, i32 }) %return) #0 !dbg !4 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %tuple.elem0.tuple.elem = getelementptr inbounds nuw { i32, i32 }, ptr %return, i32 0, i32 0, !dbg !8
// CHECK:STDOUT: %tuple.elem1.tuple.elem = getelementptr inbounds nuw { i32, i32 }, ptr %return, i32 0, i32 1, !dbg !8
// CHECK:STDOUT: call void @llvm.memcpy.p0.p0.i64(ptr align 4 %return, ptr align 4 @tuple.21c.loc12_37, i64 8, i1 false), !dbg !9
// CHECK:STDOUT: ret void, !dbg !9
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define void @_CB.Main(ptr sret([2 x i32]) %return) #0 !dbg !10 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %.loc14_39.3.array.index = getelementptr inbounds [2 x i32], ptr %return, i32 0, i64 0, !dbg !11
// CHECK:STDOUT: %.loc14_39.6.array.index = getelementptr inbounds [2 x i32], ptr %return, i32 0, i64 1, !dbg !11
// CHECK:STDOUT: call void @llvm.memcpy.p0.p0.i64(ptr align 4 %return, ptr align 4 @array.loc14_40, i64 8, i1 false), !dbg !12
// CHECK:STDOUT: ret void, !dbg !12
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define void @main() #0 !dbg !13 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %a.var = alloca [2 x i32], align 4, !dbg !16
// CHECK:STDOUT: %.loc17_28.1.temp = alloca { i32, i32 }, align 8, !dbg !17
// CHECK:STDOUT: %b.var = alloca i32, align 4, !dbg !18
// CHECK:STDOUT: %c.var = alloca i32, align 4, !dbg !19
// CHECK:STDOUT: %d.var = alloca i32, align 4, !dbg !20
// CHECK:STDOUT: %.loc20_18.1.temp = alloca [2 x i32], align 4, !dbg !21
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %a.var), !dbg !16
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc17_28.1.temp), !dbg !17
// CHECK:STDOUT: call void @_CA.Main(ptr %.loc17_28.1.temp), !dbg !17
// CHECK:STDOUT: %tuple.elem0.tuple.elem = getelementptr inbounds nuw { i32, i32 }, ptr %.loc17_28.1.temp, i32 0, i32 0, !dbg !17
// CHECK:STDOUT: %.loc17_28.3 = load i32, ptr %tuple.elem0.tuple.elem, align 4, !dbg !17
// CHECK:STDOUT: %.loc17_28.4.array.index = getelementptr inbounds [2 x i32], ptr %a.var, i32 0, i64 0, !dbg !17
// CHECK:STDOUT: store i32 %.loc17_28.3, ptr %.loc17_28.4.array.index, align 4, !dbg !17
// CHECK:STDOUT: %tuple.elem1.tuple.elem = getelementptr inbounds nuw { i32, i32 }, ptr %.loc17_28.1.temp, i32 0, i32 1, !dbg !17
// CHECK:STDOUT: %.loc17_28.6 = load i32, ptr %tuple.elem1.tuple.elem, align 4, !dbg !17
// CHECK:STDOUT: %.loc17_28.7.array.index = getelementptr inbounds [2 x i32], ptr %a.var, i32 0, i64 1, !dbg !17
// CHECK:STDOUT: store i32 %.loc17_28.6, ptr %.loc17_28.7.array.index, align 4, !dbg !17
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %b.var), !dbg !18
// CHECK:STDOUT: store i32 1, ptr %b.var, align 4, !dbg !18
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %c.var), !dbg !19
// CHECK:STDOUT: %.loc19_18 = load i32, ptr %b.var, align 4, !dbg !22
// CHECK:STDOUT: %.loc19_19.1.array.index = getelementptr inbounds [2 x i32], ptr %a.var, i32 0, i32 %.loc19_18, !dbg !23
// CHECK:STDOUT: %.loc19_19.2 = load i32, ptr %.loc19_19.1.array.index, align 4, !dbg !23
// CHECK:STDOUT: store i32 %.loc19_19.2, ptr %c.var, align 4, !dbg !19
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %d.var), !dbg !20
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %.loc20_18.1.temp), !dbg !21
// CHECK:STDOUT: call void @_CB.Main(ptr %.loc20_18.1.temp), !dbg !21
// CHECK:STDOUT: %.loc20_21.1.array.index = getelementptr inbounds [2 x i32], ptr %.loc20_18.1.temp, i32 0, i32 1, !dbg !21
// CHECK:STDOUT: %.loc20_21.2 = load i32, ptr %.loc20_21.1.array.index, align 4, !dbg !21
// CHECK:STDOUT: store i32 %.loc20_21.2, ptr %d.var, align 4, !dbg !20
// CHECK:STDOUT: ret void, !dbg !24
// CHECK:STDOUT: }
// 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) #1
// 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)) #2
// CHECK:STDOUT:
// CHECK:STDOUT: ; uselistorder directives
// CHECK:STDOUT: uselistorder ptr @llvm.memcpy.p0.p0.i64, { 1, 0 }
// CHECK:STDOUT: uselistorder ptr @llvm.lifetime.start.p0, { 5, 4, 3, 2, 1, 0 }
// CHECK:STDOUT:
// CHECK:STDOUT: attributes #0 = { nounwind }
// CHECK:STDOUT: attributes #1 = { nocallback nofree nounwind willreturn memory(argmem: readwrite) }
// CHECK:STDOUT: attributes #2 = { nocallback nofree nosync 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: "array_element_access.carbon", directory: "")
// CHECK:STDOUT: !4 = distinct !DISubprogram(name: "A", linkageName: "_CA.Main", scope: null, file: !3, line: 12, type: !5, spFlags: DISPFlagDefinition, unit: !2)
// CHECK:STDOUT: !5 = !DISubroutineType(types: !6)
// CHECK:STDOUT: !6 = !{!7}
// CHECK:STDOUT: !7 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 8)
// CHECK:STDOUT: !8 = !DILocation(line: 12, column: 31, scope: !4)
// CHECK:STDOUT: !9 = !DILocation(line: 12, column: 24, scope: !4)
// CHECK:STDOUT: !10 = distinct !DISubprogram(name: "B", linkageName: "_CB.Main", scope: null, file: !3, line: 14, type: !5, spFlags: DISPFlagDefinition, unit: !2)
// CHECK:STDOUT: !11 = !DILocation(line: 14, column: 34, scope: !10)
// CHECK:STDOUT: !12 = !DILocation(line: 14, column: 27, scope: !10)
// CHECK:STDOUT: !13 = distinct !DISubprogram(name: "Run", linkageName: "main", scope: null, file: !3, line: 16, type: !14, spFlags: DISPFlagDefinition, unit: !2)
// CHECK:STDOUT: !14 = !DISubroutineType(types: !15)
// CHECK:STDOUT: !15 = !{null}
// CHECK:STDOUT: !16 = !DILocation(line: 17, column: 3, scope: !13)
// CHECK:STDOUT: !17 = !DILocation(line: 17, column: 26, scope: !13)
// CHECK:STDOUT: !18 = !DILocation(line: 18, column: 3, scope: !13)
// CHECK:STDOUT: !19 = !DILocation(line: 19, column: 3, scope: !13)
// CHECK:STDOUT: !20 = !DILocation(line: 20, column: 3, scope: !13)
// CHECK:STDOUT: !21 = !DILocation(line: 20, column: 16, scope: !13)
// CHECK:STDOUT: !22 = !DILocation(line: 19, column: 18, scope: !13)
// CHECK:STDOUT: !23 = !DILocation(line: 19, column: 16, scope: !13)
// CHECK:STDOUT: !24 = !DILocation(line: 16, column: 1, scope: !13)
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