[CIR] Add initial support for idiom recognizing std::find

- Identify such calls and produce a remark. Next step is to map
this to a CIR operation representing std::find, which should
come next.
- Add new `-fclangir-idiom-recognizer=` option, used to control
remark options for now.

Author: bcardosolopes

clang/include/clang/Frontend/FrontendOptions.h

@@ -462,6 +462,7 @@ class FrontendOptions {
   frontend::MLIRDialectKind MLIRTargetDialect;
 
   std::string ClangIRLifetimeCheckOpts;
+  std::string ClangIRIdiomRecognizerOpts;
 
   /// The input kind, either specified via -x argument or deduced from the input
   /// file name.

clang/lib/CIR/FrontendAction/CIRGenAction.cpp

@@ -60,6 +60,8 @@ using namespace cir;
 using namespace clang;
 
 static std::string sanitizePassOptions(llvm::StringRef o) {
+  if (o.empty())
+    return "";
   std::string opts{o};
   // MLIR pass options are space separated, but we use ';' in clang since
   // space aren't well supported, switch it back.
@@ -172,15 +174,18 @@ class CIRGenConsumer : public clang::ASTConsumer {
       // Sanitize passes options. MLIR uses spaces between pass options
       // and since that's hard to fly in clang, we currently use ';'.
       std::string lifetimeOpts;
+      std::string idiomRecognizerOpts;
       if (feOptions.ClangIRLifetimeCheck)
         lifetimeOpts = sanitizePassOptions(feOptions.ClangIRLifetimeCheckOpts);
+      idiomRecognizerOpts =
+          sanitizePassOptions(feOptions.ClangIRIdiomRecognizerOpts);
 
       // Setup and run CIR pipeline.
       bool passOptParsingFailure = false;
       if (runCIRToCIRPasses(mlirMod, mlirCtx.get(), C,
                             !feOptions.ClangIRDisableCIRVerifier,
                             feOptions.ClangIRLifetimeCheck, lifetimeOpts,
-                            passOptParsingFailure)
+                            idiomRecognizerOpts, passOptParsingFailure)
               .failed()) {
         if (passOptParsingFailure)
           diagnosticsEngine.Report(diag::err_drv_cir_pass_opt_parsing)

clang/lib/Frontend/CompilerInvocation.cpp

@@ -3187,6 +3187,10 @@ static bool ParseFrontendArgs(FrontendOptions &Opts, ArgList &Args,
     Opts.ClangIRLifetimeCheckOpts = A->getValue();
   }
 
+  if (Args.hasArg(OPT_fclangir_idiom_recognizer_EQ))
+    Opts.AuxTargetCPU =
+        std::string(Args.getLastArgValue(OPT_fclangir_idiom_recognizer_EQ));
+
   if (Args.hasArg(OPT_aux_target_cpu))
     Opts.AuxTargetCPU = std::string(Args.getLastArgValue(OPT_aux_target_cpu));
   if (Args.hasArg(OPT_aux_target_feature))