PR19767: DebugInfo emission of pointer constants.

In refactoring DwarfUnit::isUnsignedDIType I restricted it to only work
on values with signedness (unsigned or signed), asserting on anything
else (which did uncover some bugs). But it turns out that we do need to
emit constants of signless data, such as pointer constants - only null
pointer constants are known to need this so far, but it's conceivable
that there might be non-null pointer constants at some point (hardcoded
address offsets for device drivers?).

This patch just uses 'unsigned' for signless data such as pointer
constants. Arguably we could use signless representations
(DW_FORM_dataN) instead, allowing a trinary result from isUnsignedDIType
(signed, unsigned, signless), but this seems reasonable for now.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209223 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 13 insertions, 2 deletions

diff --git a/lib/CodeGen/AsmPrinter/DwarfUnit.cpp b/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
index 8adf78ca85..6b54173069 100644
--- a/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
+++ b/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
@@ -749,8 +749,19 @@ void DwarfUnit::addBlockByrefAddress(const DbgVariable &DV, DIE &Die,
 static bool isUnsignedDIType(DwarfDebug *DD, DIType Ty) {
   DIDerivedType DTy(Ty);
   if (DTy.isDerivedType()) {
-    if (DIType Deriv = DD->resolve(DTy.getTypeDerivedFrom()))
-      return isUnsignedDIType(DD, Deriv);
+    dwarf::Tag T = (dwarf::Tag)Ty.getTag();
+    // Encode pointer constants as unsigned bytes. This is used at least for
+    // null pointer constant emission. Maybe DW_TAG_reference_type should be
+    // accepted here too, if there are ways to produce compile-time constant
+    // references.
+    if (T == dwarf::DW_TAG_pointer_type ||
+        T == dwarf::DW_TAG_ptr_to_member_type)
+      return true;
+    assert(T == dwarf::DW_TAG_typedef || T == dwarf::DW_TAG_const_type ||
+           T == dwarf::DW_TAG_volatile_type ||
+           T == dwarf::DW_TAG_restrict_type);
+    if (DITypeRef Deriv = DTy.getTypeDerivedFrom())
+      return isUnsignedDIType(DD, DD->resolve(Deriv));
     // FIXME: Enums without a fixed underlying type have unknown signedness
     // here, leading to incorrectly emitted constants.
     assert(DTy.getTag() == dwarf::DW_TAG_enumeration_type);