[flang][debug] Don't generate debug for compiler-generated variables (llvm#112423)

Flang generates many globals to handle derived types. There was a check
in debug info to filter them based on the information that their names
start with a period. This changed since PR#104859 where 'X' is being
used instead of '.'.

This PR fixes this issue by also adding 'X' in that list. As user
variables gets lower cased by the NameUniquer, there is no risk that
those will be filtered out. I added a test for that to be sure.

Author: abidh

flang/include/flang/Optimizer/Support/InternalNames.h

@@ -184,6 +184,10 @@ struct NameUniquer {
 
   static std::string replaceSpecialSymbols(const std::string &name);
 
+  /// Returns true if the passed name denotes a special symbol (e.g. global
+  /// symbol generated for derived type description).
+  static bool isSpecialSymbol(llvm::StringRef name);
+
 private:
   static std::string intAsString(std::int64_t i);
   static std::string doKind(std::int64_t kind);

flang/lib/Optimizer/Support/InternalNames.cpp

@@ -411,3 +411,7 @@ fir::NameUniquer::dropTypeConversionMarkers(llvm::StringRef mangledTypeName) {
 std::string fir::NameUniquer::replaceSpecialSymbols(const std::string &name) {
   return std::regex_replace(name, std::regex{"\\."}, "X");
 }
+
+bool fir::NameUniquer::isSpecialSymbol(llvm::StringRef name) {
+  return !name.empty() && (name[0] == '.' || name[0] == 'X');
+}

flang/lib/Optimizer/Transforms/AddDebugInfo.cpp

@@ -211,10 +211,7 @@ void AddDebugInfoPass::handleGlobalOp(fir::GlobalOp globalOp,
   if (result.first != fir::NameUniquer::NameKind::VARIABLE)
     return;
 
-  // Discard entries that describe a derived type. Usually start with '.c.',
-  // '.dt.' or '.n.'. It would be better if result of the deconstruct had a flag
-  // for such values so that we dont have to look at string values.
-  if (!result.second.name.empty() && result.second.name[0] == '.')
+  if (fir::NameUniquer::isSpecialSymbol(result.second.name))
     return;
 
   unsigned line = getLineFromLoc(globalOp.getLoc());

flang/test/Integration/debug-extra-global-2.f90

@@ -0,0 +1,8 @@
+! RUN: %flang_fc1 -emit-llvm -debug-info-kind=standalone %s -o - | FileCheck  %s
+
+module m
+  integer XcX
+end
+
+! Test that global starting with 'X' don't get filtered.
+! CHECK: !DIGlobalVariable(name: "xcx", linkageName: "_QMmExcx"{{.*}})

flang/test/Integration/debug-extra-global.f90

@@ -0,0 +1,14 @@
+! RUN: %flang_fc1 -emit-llvm -debug-info-kind=standalone %s -o - | FileCheck  %s
+
+program test
+ type t1
+   integer :: XcX
+   integer :: xdtx
+ end type
+  type(t1) :: var
+  var%XcX = 2
+  var%xdtx = 3
+end
+
+! Test that there is no debug info for compiler generated globals.
+! CHECK-NOT: DIGlobalVariable

flang/test/Transforms/debug-extra-global.fir

@@ -0,0 +1,18 @@
+// RUN: fir-opt --add-debug-info --mlir-print-debuginfo %s | FileCheck %s
+
+module attributes {dlti.dl_spec = #dlti.dl_spec<>} {
+  fir.global linkonce_odr @_QFEXnXxcx constant target : !fir.char<1,3> {
+    %0 = fir.string_lit "xcx"(3) : !fir.char<1,3>
+    fir.has_value %0 : !fir.char<1,3>
+  } loc(#loc1)
+  fir.global linkonce_odr @_QFEXnXxdtx constant target : !fir.char<1,4> {
+    %0 = fir.string_lit "xdtx"(4) : !fir.char<1,4>
+    fir.has_value %0 : !fir.char<1,4>
+  } loc(#loc1)
+}
+#loc1 = loc("derived.f90":24:1)
+
+// Test that no di_global_variable gets created for these compile generated
+// globals.
+
+// CHECK-NOT: #di_global_variable