[ExportVerilog] Add verilog debug locations to output MLIR (#6092)

Use the PrettyPrinter CallbackToken API, to record print events and store the
 verilog output locations for each operation. Record the print begin and end
 location of each op. This has a side-effect of updating the IR, location
 attribute of the op is updated to include the verilog location range. `FusedLoc`
 is used to record the location ranges and each op can correspond to multiple
verilog locations.
This feature is disabled by default under an emission flag `emitVerilogLocations`.

include/circt/Support/LoweringOptions.h

@@ -163,6 +163,9 @@ struct LoweringOptions {
   /// This is used to avoid stricter lint warnings which, e.g., treat "REG" as a
   /// Verilog keyword.
   bool caseInsensitiveKeywords = false;
+
+  /// If true, then update the the mlir to include output verilog locations.
+  bool emitVerilogLocations = false;
 };
 } // namespace circt
 

include/circt/Support/PrettyPrinterHelpers.h

@@ -240,6 +240,8 @@ struct PPSaveString {
 template <typename PPTy = PrettyPrinter>
 class TokenStream : public TokenBuilder<PPTy> {
   using Base = TokenBuilder<PPTy>;
+
+protected:
   TokenStringSaver &saver;
 
 public:
@@ -369,6 +371,28 @@ class TokenStream : public TokenBuilder<PPTy> {
   }
 };
 
+/// Wrap the TokenStream with a helper for CallbackTokens, to record the print
+/// events on the stream.
+template <typename CallableType, typename DataType,
+          typename PPTy = PrettyPrinter>
+class TokenStreamWithCallback : public TokenStream<PPTy> {
+  using Base = TokenStream<PPTy>;
+  PrintEventAndStorageListener<CallableType, DataType> &saver;
+
+  const bool enableCallback;
+
+public:
+  TokenStreamWithCallback(
+      PPTy &pp, PrintEventAndStorageListener<CallableType, DataType> &saver,
+      bool enableCallback)
+      : TokenStream<PPTy>(pp, saver), saver(saver),
+        enableCallback(enableCallback) {}
+  /// Add a Callback token.
+  void addCallback(DataType d) {
+    if (enableCallback)
+      Base::addToken(saver.getToken(d));
+  }
+};
 } // end namespace pretty
 } // end namespace circt