Add LLVM IR debug info support for Fortran COMMON blocks

    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

1 files changed, 13 insertions, 0 deletions

diff --git a/llvm/lib/IR/AsmWriter.cpp b/llvm/lib/IR/AsmWriter.cpp
index ad6c2c8e883..376262b8462 100644
--- a/llvm/lib/IR/AsmWriter.cpp
+++ b/llvm/lib/IR/AsmWriter.cpp
@@ -2001,6 +2001,19 @@ static void writeDINamespace(raw_ostream &Out, const DINamespace *N,
   Out << ")";
 }
 
+static void writeDICommonBlock(raw_ostream &Out, const DICommonBlock *N,
+                               TypePrinting *TypePrinter, SlotTracker *Machine,
+                               const Module *Context) {
+  Out << "!DICommonBlock(";
+  MDFieldPrinter Printer(Out, TypePrinter, Machine, Context);
+  Printer.printMetadata("scope", N->getRawScope(), false);
+  Printer.printMetadata("declaration", N->getRawDecl(), false);
+  Printer.printString("name", N->getName());
+  Printer.printMetadata("file", N->getRawFile());
+  Printer.printInt("line", N->getLineNo());
+  Out << ")";
+}
+
 static void writeDIMacro(raw_ostream &Out, const DIMacro *N,
                          TypePrinting *TypePrinter, SlotTracker *Machine,
                          const Module *Context) {