[PATCH] D54327: Adding debug info to support Fortran (part 3)

[Eric Schweitz via Phabricator via llvm-commits]

schweitz created this revision.
schweitz added reviewers: aprantl, hfinkel, probinson, greened, deadalnix.
schweitz added a project: debug-info.
Herald added subscribers: llvm-commits, JDevlieghere.

3. Fortran COMMON Block

COMMON blocks are a feature of Fortran that has no direct analog in C languages, but they are similar to data sections in assembly language programming. A COMMON block is a named area of memory that holds a collection of variables. Fortran subprograms may map the COMMON block memory area to their own, possibly distinct, non-empty list of variables.  A Fortran COMMON block might look like the following example.

COMMON /ALPHA/ I, J

For this construct, the compiler generates a new scope-like DI construct (!DICommonBlock) into which variables (see I, J above) can be placed. As the common block implies a range of storage with global lifetime, the !DICommonBlock refers to a !DIGlobalVariable.  The Fortran variable that comprise the COMMON block are also linked via metadata to offsets within the global variable that stands for the entire common block.

@alpha_ = common global %alphabytes_  zeroinitializer, align 64, !dbg !27, !dbg !30, !dbg !33
!14 = distinct !DISubprogram(…)
!20 = distinct !DICommonBlock(scope: !14, declaration: !25, name: "alpha")
!25 = distinct !DIGlobalVariable(scope: !20, name: "common alpha", type: !24)
!27 = !DIGlobalVariableExpression(var: !25, expr: !DIExpression())
!29 = distinct !DIGlobalVariable(scope: !20, name: "i", file: !3, type: !28)
!30 = !DIGlobalVariableExpression(var: !29, expr: !DIExpression())
!31 = distinct !DIGlobalVariable(scope: !20, name: "j", file: !3, type: !28)
!32 = !DIExpression(DW_OP_plus_uconst, 4)
!33 = !DIGlobalVariableExpression(var: !31, expr: !32)

The DWARF generated for this is as follows.

DW_TAG_common_block:
DW_AT_name: alpha
DW_AT_location: @alpha_+0
DW_TAG_variable:
DW_AT_name: common alpha
DW_AT_type: array of 8 bytes
DW_AT_location: @alpha_+0
DW_TAG_variable:
DW_AT_name: i
DW_AT_type: integer*4
DW_AT_location: @alpha+0
DW_TAG_variable:
DW_AT_name: j
DW_AT_type: integer*4
DW_AT_location: @alpha+4


Repository:
  rL LLVM

https://reviews.llvm.org/D54327

Files:
  include/llvm-c/DebugInfo.h
  include/llvm/Bitcode/LLVMBitCodes.h
  include/llvm/IR/DIBuilder.h
  include/llvm/IR/DebugInfoMetadata.h
  include/llvm/IR/Metadata.def
  lib/AsmParser/LLParser.cpp
  lib/Bitcode/Reader/MetadataLoader.cpp
  lib/Bitcode/Writer/BitcodeWriter.cpp
  lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
  lib/CodeGen/AsmPrinter/DwarfCompileUnit.h
  lib/CodeGen/AsmPrinter/DwarfUnit.cpp
  lib/IR/AsmWriter.cpp
  lib/IR/DIBuilder.cpp
  lib/IR/DebugInfoMetadata.cpp
  lib/IR/LLVMContextImpl.h
  lib/IR/Verifier.cpp
  test/DebugInfo/DICommonBlock.ll

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