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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
Patch by Eric Schweitz!
Differential Revision: https://reviews.llvm.org/D54327
llvm-svn: 357934
27 lines
1.4 KiB
LLVM
27 lines
1.4 KiB
LLVM
; RUN: llvm-as < %s | llvm-dis | llvm-as | llvm-dis | FileCheck %s
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; CHECK-DAG: [[MD:![0-9]+]] = !DICommonBlock({{.*}}name: "a"
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; CHECK-DAG: !DIGlobalVariable({{.*}}name: "c",{{.*}}scope: [[MD]]
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@common_a = common global [32 x i8] zeroinitializer, align 8, !dbg !13, !dbg !15
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!llvm.dbg.cu = !{!0}
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!llvm.module.flags = !{!6, !7}
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!llvm.ident = !{!8}
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!0 = distinct !DICompileUnit(language: DW_LANG_Fortran90, file: !1, producer: "PGI Fortran", isOptimized: false, runtimeVersion: 2, emissionKind: FullDebug, retainedTypes: !14, globals: !3)
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!1 = !DIFile(filename: "none.f90", directory: "/not/here/")
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!2 = distinct !DIGlobalVariable(scope: !5, name: "c", file: !1, type: !12, isDefinition: true)
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!3 = !{!13, !15}
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!4 = distinct !DIGlobalVariable(scope: !5, name: "COMMON /foo/", file: !1, line: 4, isLocal: false, isDefinition: true, type: !12)
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!5 = !DICommonBlock(scope: !9, declaration: !4, name: "a", file: !1, line: 4)
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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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!8 = !{!"PGI Fortran"}
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!9 = distinct !DISubprogram(name: "subrtn", scope: !0, file: !1, line: 1, type: !10, isLocal: false, isDefinition: true, unit: !0)
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!10 = !DISubroutineType(types: !11)
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!11 = !{!12, !12}
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!12 = !DIBasicType(name: "int", size: 32)
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!13 = !DIGlobalVariableExpression(var: !4, expr: !DIExpression())
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!14 = !{!12, !10}
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!15 = !DIGlobalVariableExpression(var: !2, expr: !DIExpression(DW_OP_plus_uconst, 4))
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