DebugInfo: support for DW_FORM_implicit_const

Support for DW_FORM_implicit_const DWARFv5 feature.
When this form is used attribute value goes to .debug_abbrev section (as SLEB).
As this form would break any debug tool which doesn't support DWARFv5
it is guarded by dwarf version check. Attempt to use this form with
dwarf version <= 4 is considered a fatal error.

Differential Revision: https://reviews.llvm.org/D28456

llvm-svn: 291599

2 files changed, 17 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DIE.cpp b/llvm/lib/CodeGen/AsmPrinter/DIE.cpp
index 8ae2f2487ca..a8a3b30d5b6 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DIE.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DIE.cpp
@@ -79,6 +79,13 @@ void DIEAbbrev::Emit(const AsmPrinter *AP) const {
     // Emit form type.
     AP->EmitULEB128(AttrData.getForm(),
                     dwarf::FormEncodingString(AttrData.getForm()).data());
+
+    // Emit value for DW_FORM_implicit_const.
+    if (AttrData.getForm() == dwarf::DW_FORM_implicit_const) {
+      assert(AP->getDwarfVersion() >= 5 &&
+            "DW_FORM_implicit_const is supported starting from DWARFv5");
+      AP->EmitSLEB128(AttrData.getValue());
+    }
   }
 
   // Mark end of abbreviation.
@@ -160,7 +167,11 @@ DIE *DIE::getParent() const {
 DIEAbbrev DIE::generateAbbrev() const {
   DIEAbbrev Abbrev(Tag, hasChildren());
   for (const DIEValue &V : values())
-    Abbrev.AddAttribute(V.getAttribute(), V.getForm());
+    if (V.getForm() == dwarf::DW_FORM_implicit_const)
+      Abbrev.AddImplicitConstAttribute(V.getAttribute(),
+                                       V.getDIEInteger().getValue());
+    else
+      Abbrev.AddAttribute(V.getAttribute(), V.getForm());
   return Abbrev;
 }
 
@@ -342,6 +353,8 @@ void DIEValue::dump() const {
 ///
 void DIEInteger::EmitValue(const AsmPrinter *Asm, dwarf::Form Form) const {
   switch (Form) {
+  case dwarf::DW_FORM_implicit_const:
+    LLVM_FALLTHROUGH;
   case dwarf::DW_FORM_flag_present:
     // Emit something to keep the lines and comments in sync.
     // FIXME: Is there a better way to do this?
@@ -406,6 +419,7 @@ void DIEInteger::EmitValue(const AsmPrinter *Asm, dwarf::Form Form) const {
 ///
 unsigned DIEInteger::SizeOf(const AsmPrinter *AP, dwarf::Form Form) const {
   switch (Form) {
+  case dwarf::DW_FORM_implicit_const: LLVM_FALLTHROUGH;
   case dwarf::DW_FORM_flag_present: return 0;
   case dwarf::DW_FORM_flag:  LLVM_FALLTHROUGH;
   case dwarf::DW_FORM_ref1:  LLVM_FALLTHROUGH;
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
index 4f90245c6d4..2a866c071f5 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
@@ -200,6 +200,8 @@ void DwarfUnit::addUInt(DIEValueList &Die, dwarf::Attribute Attribute,
                         Optional<dwarf::Form> Form, uint64_t Integer) {
   if (!Form)
     Form = DIEInteger::BestForm(false, Integer);
+  assert(Form != dwarf::DW_FORM_implicit_const &&
+         "DW_FORM_implicit_const is used only for signed integers");
   Die.addValue(DIEValueAllocator, Attribute, *Form, DIEInteger(Integer));
 }