[CGDebugInfo] Emit subprograms for decls when AT_tail_call is understood (reland with fixes)

Currently, clang emits subprograms for declared functions when the
target debugger or DWARF standard is known to support entry values
(DW_OP_entry_value & the GNU equivalent).

Treat DW_AT_tail_call the same way to allow debuggers to follow cross-TU
tail calls.

Pre-patch debug session with a cross-TU tail call:

```
  * frame #0: 0x0000000100000fa4 main`target at b.c:4:3 [opt]
    frame #1: 0x0000000100000f99 main`main at a.c:8:10 [opt]
```

Post-patch (note that the tail-calling frame, "helper", is visible):

```
  * frame #0: 0x0000000100000fa4 main`target at b.c:4:3 [opt]
    frame #1: 0x0000000100000f80 main`helper [opt] [artificial]
    frame #2: 0x0000000100000f99 main`main at a.c:8:10 [opt]
```

This was reverted in 5b9a072c because it attached declaration
subprograms to inlinable builtin calls, which interacted badly with the
MergeICmps pass. The fix is to not attach declarations to builtins.

rdar://46577651

Differential Revision: https://reviews.llvm.org/D69743

1 files changed, 18 insertions, 10 deletions

diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
index 75c4b2ae233..116517a9cb9 100644
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -3765,21 +3765,29 @@ void CGDebugInfo::EmitFunctionDecl(GlobalDecl GD, SourceLocation Loc,
 void CGDebugInfo::EmitFuncDeclForCallSite(llvm::CallBase *CallOrInvoke,
                                           QualType CalleeType,
                                           const FunctionDecl *CalleeDecl) {
-  auto &CGOpts = CGM.getCodeGenOpts();
-  if (!CGOpts.EnableDebugEntryValues || !CGM.getLangOpts().Optimize ||
-      !CallOrInvoke)
+  if (!CallOrInvoke)
     return;
-
   auto *Func = CallOrInvoke->getCalledFunction();
   if (!Func)
     return;
+  if (Func->getSubprogram())
+    return;
+
+  // Do not emit a declaration subprogram for a builtin or if call site info
+  // isn't required. Also, elide declarations for functions with reserved names,
+  // as call site-related features aren't interesting in this case (& also, the
+  // compiler may emit calls to these functions without debug locations, which
+  // makes the verifier complain).
+  if (CalleeDecl->getBuiltinID() != 0 ||
+      getCallSiteRelatedAttrs() == llvm::DINode::FlagZero)
+    return;
+  if (const auto *Id = CalleeDecl->getIdentifier())
+    if (Id->isReservedName())
+      return;
 
   // If there is no DISubprogram attached to the function being called,
   // create the one describing the function in order to have complete
   // call site debug info.
-  if (Func->getSubprogram())
-    return;
-
   if (!CalleeDecl->isStatic() && !CalleeDecl->isInlined())
     EmitFunctionDecl(CalleeDecl, CalleeDecl->getLocation(), CalleeType, Func);
 }
@@ -4841,10 +4849,10 @@ llvm::DINode::DIFlags CGDebugInfo::getCallSiteRelatedAttrs() const {
   bool SupportsDWARFv4Ext =
       CGM.getCodeGenOpts().DwarfVersion == 4 &&
       (CGM.getCodeGenOpts().getDebuggerTuning() == llvm::DebuggerKind::LLDB ||
-       (CGM.getCodeGenOpts().EnableDebugEntryValues &&
-       CGM.getCodeGenOpts().getDebuggerTuning() == llvm::DebuggerKind::GDB));
+       CGM.getCodeGenOpts().getDebuggerTuning() == llvm::DebuggerKind::GDB);
 
-  if (!SupportsDWARFv4Ext && CGM.getCodeGenOpts().DwarfVersion < 5)
+  if (!SupportsDWARFv4Ext && CGM.getCodeGenOpts().DwarfVersion < 5 &&
+      !CGM.getCodeGenOpts().EnableDebugEntryValues)
     return llvm::DINode::FlagZero;
 
   return llvm::DINode::FlagAllCallsDescribed;