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, 28 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
index fbb7a5773e7..c1e8ffec75a 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp
@@ -123,7 +123,9 @@ DIE *DwarfCompileUnit::getOrCreateGlobalVariableDIE(
 
   // Construct the context before querying for the existence of the DIE in
   // case such construction creates the DIE.
-  DIE *ContextDIE = getOrCreateContextDIE(GVContext);
+  auto *CB = GVContext ? dyn_cast<DICommonBlock>(GVContext) : nullptr;
+  DIE *ContextDIE = CB ? getOrCreateCommonBlock(CB, GlobalExprs)
+    : getOrCreateContextDIE(GVContext);
 
   // Add to map.
   DIE *VariableDIE = &createAndAddDIE(GV->getTag(), *ContextDIE, GV);
@@ -166,6 +168,13 @@ DIE *DwarfCompileUnit::getOrCreateGlobalVariableDIE(
     addTemplateParams(*VariableDIE, DINodeArray(TP));
 
   // Add location.
+  addLocationAttribute(VariableDIE, GV, GlobalExprs);
+
+  return VariableDIE;
+}
+
+void DwarfCompileUnit::addLocationAttribute(
+    DIE *VariableDIE, const DIGlobalVariable *GV, ArrayRef<GlobalExpr> GlobalExprs) {
   bool addToAccelTable = false;
   DIELoc *Loc = nullptr;
   Optional<unsigned> NVPTXAddressSpace;
@@ -288,8 +297,25 @@ DIE *DwarfCompileUnit::getOrCreateGlobalVariableDIE(
         DD->useAllLinkageNames())
       DD->addAccelName(*CUNode, GV->getLinkageName(), *VariableDIE);
   }
+}
 
-  return VariableDIE;
+DIE *DwarfCompileUnit::getOrCreateCommonBlock(
+    const DICommonBlock *CB, ArrayRef<GlobalExpr> GlobalExprs) {
+  // Construct the context before querying for the existence of the DIE in case
+  // such construction creates the DIE.
+  DIE *ContextDIE = getOrCreateContextDIE(CB->getScope());
+
+  if (DIE *NDie = getDIE(CB))
+    return NDie;
+  DIE &NDie = createAndAddDIE(dwarf::DW_TAG_common_block, *ContextDIE, CB);
+  StringRef Name = CB->getName().empty() ? "_BLNK_" : CB->getName();
+  addString(NDie, dwarf::DW_AT_name, Name);
+  addGlobalName(Name, NDie, CB->getScope());
+  if (CB->getFile())
+    addSourceLine(NDie, CB->getLineNo(), CB->getFile());
+  if (DIGlobalVariable *V = CB->getDecl())
+    getCU().addLocationAttribute(&NDie, V, GlobalExprs);
+  return &NDie;
 }
 
 void DwarfCompileUnit::addRange(RangeSpan Range) {