llvm-dwarfdump: Fix DWARF-5 DW_FORM_implicit_const (used by GCC)

Differential Revision: https://reviews.llvm.org/D98195

(cherry picked from commit 4289a7f)

Author: jankratochvil

llvm/include/llvm/DebugInfo/DWARF/DWARFAbbreviationDeclaration.h

@@ -111,6 +111,16 @@ class DWARFAbbreviationDeclaration {
     return AttributeSpecs[idx].Attr;
   }
 
+  bool getAttrIsImplicitConstByIndex(uint32_t idx) const {
+    assert(idx < AttributeSpecs.size());
+    return AttributeSpecs[idx].isImplicitConst();
+  }
+
+  int64_t getAttrImplicitConstValueByIndex(uint32_t idx) const {
+    assert(idx < AttributeSpecs.size());
+    return AttributeSpecs[idx].getImplicitConstValue();
+  }
+
   /// Get the index of the specified attribute.
   ///
   /// Searches the this abbreviation declaration for the index of the specified

llvm/lib/DebugInfo/DWARF/DWARFDie.cpp

@@ -632,15 +632,8 @@ void DWARFDie::dump(raw_ostream &OS, unsigned Indent,
         OS << '\n';
 
         // Dump all data in the DIE for the attributes.
-        for (const DWARFAttribute &AttrValue : attributes()) {
-          if (AttrValue.Value.getForm() == DW_FORM_implicit_const) {
-            // We are dumping .debug_info section ,
-            // implicit_const attribute values are not really stored here,
-            // but in .debug_abbrev section. So we just skip such attrs.
-            continue;
-          }
+        for (const DWARFAttribute &AttrValue : attributes())
           dumpAttribute(OS, *this, AttrValue, Indent, DumpOpts);
-        }
 
         DWARFDie child = getFirstChild();
         if (DumpOpts.ShowChildren && DumpOpts.ChildRecurseDepth > 0 && child) {
@@ -723,10 +716,16 @@ void DWARFDie::attribute_iterator::updateForIndex(
     // Add the previous byte size of any previous attribute value.
     AttrValue.Offset += AttrValue.ByteSize;
     uint64_t ParseOffset = AttrValue.Offset;
-    auto U = Die.getDwarfUnit();
-    assert(U && "Die must have valid DWARF unit");
-    AttrValue.Value = DWARFFormValue::createFromUnit(
-        AbbrDecl.getFormByIndex(Index), U, &ParseOffset);
+    if (AbbrDecl.getAttrIsImplicitConstByIndex(Index))
+      AttrValue.Value = DWARFFormValue::createFromSValue(
+          AbbrDecl.getFormByIndex(Index),
+          AbbrDecl.getAttrImplicitConstValueByIndex(Index));
+    else {
+      auto U = Die.getDwarfUnit();
+      assert(U && "Die must have valid DWARF unit");
+      AttrValue.Value = DWARFFormValue::createFromUnit(
+          AbbrDecl.getFormByIndex(Index), U, &ParseOffset);
+    }
     AttrValue.ByteSize = ParseOffset - AttrValue.Offset;
   } else {
     assert(Index == NumAttrs && "Indexes should be [0, NumAttrs) only");

llvm/lib/DebugInfo/DWARF/DWARFFormValue.cpp

@@ -168,6 +168,7 @@ bool DWARFFormValue::skipValue(dwarf::Form Form, DataExtractor DebugInfoData,
     case DW_FORM_line_strp:
     case DW_FORM_GNU_ref_alt:
     case DW_FORM_GNU_strp_alt:
+    case DW_FORM_implicit_const:
       if (Optional<uint8_t> FixedSize =
               dwarf::getFixedFormByteSize(Form, Params)) {
         *OffsetPtr += *FixedSize;
@@ -345,6 +346,9 @@ bool DWARFFormValue::extractValue(const DWARFDataExtractor &Data,
     case DW_FORM_ref_sig8:
       Value.uval = Data.getU64(OffsetPtr, &Err);
       break;
+    case DW_FORM_implicit_const:
+      // Value has been already set by DWARFFormValue::createFromSValue.
+      break;
     default:
       // DWARFFormValue::skipValue() will have caught this and caused all
       // DWARF DIEs to fail to be parsed, so this code is not be reachable.
@@ -482,6 +486,7 @@ void DWARFFormValue::dump(raw_ostream &OS, DIDumpOptions DumpOpts) const {
     break;
 
   case DW_FORM_sdata:
+  case DW_FORM_implicit_const:
     OS << Value.sval;
     break;
   case DW_FORM_udata:

llvm/test/DebugInfo/implicit-const-test2.s

@@ -0,0 +1,34 @@
+# REQUIRES: x86-registered-target
+
+# RUN: llvm-mc --filetype=obj --triple=x86_64-pc-linux %s -o %t.o -g
+
+# RUN: llvm-dwarfdump -v %t.o | FileCheck %s
+
+# CHECK:      [1] DW_TAG_compile_unit	DW_CHILDREN_no
+# CHECK-NEXT: DW_AT_language	DW_FORM_implicit_const	29
+
+# CHECK:      0x0000000c: DW_TAG_compile_unit [1]  
+# CHECK-NEXT: DW_AT_language [DW_FORM_implicit_const]	(DW_LANG_C11)
+
+	.section	.debug_info,"",@progbits
+.Ldebug_info0:
+	.long	.Ldebug_info0_end - .Ldebug_info0_start	# Length of Compilation Unit Info
+.Ldebug_info0_start:
+	.value	0x5	# DWARF version number
+	.byte	0x1	# DW_UT_compile
+	.byte	0x8	# Pointer Size (in bytes)
+	.long	.Ldebug_abbrev0	# Offset Into Abbrev. Section
+	.uleb128 0x1	# (DIE DW_TAG_compile_unit)
+			# DW_AT_language
+.Ldebug_info0_end:
+	.section	.debug_abbrev,"",@progbits
+.Ldebug_abbrev0:
+	.uleb128 0x1	# (abbrev code)
+	.uleb128 0x11	# (TAG: DW_TAG_compile_unit)
+	.byte	0x0	# DW_children_no
+	.uleb128 0x13	# (DW_AT_language)
+	.uleb128 0x21   # (DW_FORM_implicit_const)
+	.sleb128 0x1d
+	.byte	0
+	.byte	0
+	.byte	0