[CodeGen/AccelTable]: Don't emit accelerator entries for functions with no names

Summary:
We were emitting accelerator entries for functions with no name, which
is contrary to the DWARF v5 spec: "All other (i.e., *not*
DW_TAG_namespace) debugging information entries without a DW_AT_name
attribute are excluded." Besides that, a name table entry with an empty
string as a key is fairly useless.

We can sometimes end up with functions which have a DW_AT_linkage_name but no
DW_AT_name. One such example is the global-constructor-initialization functions,
which C++ compilers synthesize for each compilation unit with global
constructors.
A very strict reading of the DWARF v5 spec would suggest that we should not even
emit the accelerator entry for the linkage name in this case, but I don't think
we should go that far.

I found this when running the dwarf verifier over llvm codebase compiled
with DWARF v5 accelerator tables.

Reviewers: JDevlieghere, aprantl, dblaikie

Subscribers: vleschuk, clayborg, echristo, probinson, llvm-commits

Differential Revision: https://reviews.llvm.org/D45367

llvm-svn: 329552

1 files changed, 3 insertions, 4 deletions

diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
index 0f19700d6bb..5cd59b4da9e 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
@@ -386,13 +386,12 @@ static StringRef getObjCMethodName(StringRef In) {
 }
 
 // Add the various names to the Dwarf accelerator table names.
-// TODO: Determine whether or not we should add names for programs
-// that do not have a DW_AT_name or DW_AT_linkage_name field - this
-// is only slightly different than the lookup of non-standard ObjC names.
 void DwarfDebug::addSubprogramNames(const DISubprogram *SP, DIE &Die) {
   if (!SP->isDefinition())
     return;
-  addAccelName(SP->getName(), Die);
+
+  if (SP->getName() != "")
+    addAccelName(SP->getName(), Die);
 
   // If the linkage name is different than the name, go ahead and output
   // that as well into the name table.