[all-commits] [llvm/llvm-project] 67fb26: [DebugInfo] Add a specification attribute to LLVM ...

[Augusto Noronha via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 67fb2686fba9abd6e607ff9a09b7018b2b8ae31b
      https://github.com/llvm/llvm-project/commit/67fb2686fba9abd6e607ff9a09b7018b2b8ae31b
  Author: Augusto Noronha <anoronha at apple.com>
  Date:   2024-11-13 (Wed, 13 Nov 2024)

  Changed paths:
    M llvm/include/llvm/IR/DIBuilder.h
    M llvm/include/llvm/IR/DebugInfoMetadata.h
    M llvm/lib/AsmParser/LLParser.cpp
    M llvm/lib/Bitcode/Reader/MetadataLoader.cpp
    M llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
    M llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
    M llvm/lib/IR/AsmWriter.cpp
    M llvm/lib/IR/DIBuilder.cpp
    M llvm/lib/IR/DebugInfoMetadata.cpp
    M llvm/lib/IR/LLVMContextImpl.h
    M llvm/test/Assembler/debug-info.ll
    A llvm/test/DebugInfo/AArch64/specification.ll
    M llvm/unittests/IR/DebugTypeODRUniquingTest.cpp

  Log Message:
  -----------
  [DebugInfo] Add a specification attribute to LLVM DebugInfo (#115362)

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
```



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