[clang][codegen] Remember string used to create llvm::Regex for optimization remarks

Regular expression patterns passed through the command line are being used to create an instances of `llvm::Regex` and thrown away.

There is no API to serialize `Regex` back to the original pattern. This means we have no way to reconstruct the original pattern from command line. This is necessary for serializing `CompilerInvocation`.

This patch stores the original pattern string in `CodeGenOptions` alongside the `llvm::Regex` instance.

Reviewed By: dexonsmith, thegameg

Differential Revision: https://reviews.llvm.org/D96036

Author: jansvoboda11

clang/include/clang/Basic/CodeGenOptions.h

@@ -278,27 +278,37 @@ class CodeGenOptions : public CodeGenOptionsBase {
   /// -fsymbol-partition (see https://lld.llvm.org/Partitions.html).
   std::string SymbolPartition;
 
+  /// Regular expression and the string it was created from.
+  struct RemarkPattern {
+    std::string Pattern;
+    std::shared_ptr<llvm::Regex> Regex;
+
+    explicit operator bool() const { return Regex != nullptr; }
+
+    llvm::Regex *operator->() const { return Regex.get(); }
+  };
+
   /// Regular expression to select optimizations for which we should enable
   /// optimization remarks. Transformation passes whose name matches this
   /// expression (and support this feature), will emit a diagnostic
   /// whenever they perform a transformation. This is enabled by the
   /// -Rpass=regexp flag.
-  std::shared_ptr<llvm::Regex> OptimizationRemarkPattern;
+  RemarkPattern OptimizationRemarkPattern;
 
   /// Regular expression to select optimizations for which we should enable
   /// missed optimization remarks. Transformation passes whose name matches this
   /// expression (and support this feature), will emit a diagnostic
   /// whenever they tried but failed to perform a transformation. This is
   /// enabled by the -Rpass-missed=regexp flag.
-  std::shared_ptr<llvm::Regex> OptimizationRemarkMissedPattern;
+  RemarkPattern OptimizationRemarkMissedPattern;
 
   /// Regular expression to select optimizations for which we should enable
   /// optimization analyses. Transformation passes whose name matches this
   /// expression (and support this feature), will emit a diagnostic
   /// whenever they want to explain why they decided to apply or not apply
   /// a given transformation. This is enabled by the -Rpass-analysis=regexp
   /// flag.
-  std::shared_ptr<llvm::Regex> OptimizationRemarkAnalysisPattern;
+  RemarkPattern OptimizationRemarkAnalysisPattern;
 
   /// Set of files defining the rules for the symbol rewriting.
   std::vector<std::string> RewriteMapFiles;

clang/lib/Frontend/CompilerInvocation.cpp

@@ -1164,8 +1164,8 @@ static void parseAnalyzerConfigs(AnalyzerOptions &AnOpts,
 }
 
 /// Create a new Regex instance out of the string value in \p RpassArg.
-/// It returns a pointer to the newly generated Regex instance.
-static std::shared_ptr<llvm::Regex>
+/// It returns the string and a pointer to the newly generated Regex instance.
+static CodeGenOptions::RemarkPattern
 GenerateOptimizationRemarkRegex(DiagnosticsEngine &Diags, ArgList &Args,
                                 Arg *RpassArg) {
   StringRef Val = RpassArg->getValue();
@@ -1176,7 +1176,7 @@ GenerateOptimizationRemarkRegex(DiagnosticsEngine &Diags, ArgList &Args,
         << RegexError << RpassArg->getAsString(Args);
     Pattern.reset();
   }
-  return Pattern;
+  return {std::string(Val), Pattern};
 }
 
 static bool parseDiagnosticLevelMask(StringRef FlagName,