67fb2686fb
Add a specification attribute to LLVM DebugInfo, which is analogous
to DWARF's DW_AT_specification. According to the DWARF spec:
"A debugging information entry that represents a declaration that
completes another (earlier) non-defining declaration may have a
DW_AT_specification attribute whose value is a reference to the
debugging information entry representing the non-defining declaration."
This patch allows types to be specifications of other types. This is
used by Swift to represent generic types. For example, given this Swift
program:
```
struct MyStruct<T> {
let t: T
}
let variable = MyStruct<Int>(t: 43)
```
The Swift compiler emits (roughly) an unsubtituted type for MyStruct<T>:
```
DW_TAG_structure_type
DW_AT_name ("MyStruct")
// "$s1w8MyStructVyxGD" is a Swift mangled name roughly equivalent to
// MyStruct<T>
DW_AT_linkage_name ("$s1w8MyStructVyxGD")
// other attributes here
```
And a specification for MyStruct<Int>:
```
DW_TAG_structure_type
DW_AT_specification (<link to "MyStruct">)
// "$s1w8MyStructVySiGD" is a Swift mangled name equivalent to
// MyStruct<Int>
DW_AT_linkage_name ("$s1w8MyStructVySiGD")
DW_AT_byte_size (0x08)
// other attributes here
```
32 lines
1.2 KiB
LLVM
32 lines
1.2 KiB
LLVM
; RUN: llc %s -filetype=obj -mtriple arm64e-apple-darwin -o - \
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; RUN: | llvm-dwarfdump - | FileCheck %s
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; CHECK: DW_TAG_structure_type
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; CHECK: DW_AT_specification ({{.*}} "BaseType")
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; CHECK: DW_AT_name ("SpecificationType")
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; CHECK: DW_AT_byte_size (0x08)
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; CHECK: DW_TAG_structure_type
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; CHECK: DW_AT_name ("BaseType")
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; CHECK: DW_AT_byte_size (0x08)
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target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
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@p = common global i8* null, align 8, !dbg !0
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!llvm.dbg.cu = !{!2}
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!llvm.module.flags = !{!6, !7}
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!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
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!1 = distinct !DIGlobalVariable(name: "p", scope: !2, file: !3, line: 1, type: !11, isLocal: false, isDefinition: true)
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!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, emissionKind: FullDebug, globals: !5)
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!3 = !DIFile(filename: "/tmp/p.c", directory: "/")
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!4 = !{}
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!5 = !{!0}
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!6 = !{i32 2, !"Dwarf Version", i32 4}
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!7 = !{i32 2, !"Debug Info Version", i32 3}
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!10 = !DICompositeType(tag: DW_TAG_structure_type, name: "BaseType", file: !3, size: 64, identifier: "BaseType")
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!11 = !DICompositeType(tag: DW_TAG_structure_type, name: "SpecificationType", file: !3, size: 64, identifier: "SpecificationType", specification: !10)
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