[flang][driver] add -flang-deprecated-no-hlfir hidden option (#71820)

Patch 1/3 of the transition to use the HLFIR step by default in lowering
as described in
https://discourse.llvm.org/t/rfc-enabling-the-hlfir-lowering-by-default/72778/7

This option will allow to lower code without the HLFIR step during a
grace period as described in the RFC. It is not meant to be a long term
switch for flang.

1 files changed, 13 insertions, 0 deletions

diff --git a/flang/lib/Frontend/CompilerInvocation.cpp b/flang/lib/Frontend/CompilerInvocation.cpp
index ba2ecab..3fef377 100644
--- a/flang/lib/Frontend/CompilerInvocation.cpp
+++ b/flang/lib/Frontend/CompilerInvocation.cpp
@@ -1073,6 +1073,19 @@ bool CompilerInvocation::createFromArgs(
     res.loweringOpts.setLowerToHighLevelFIR(true);
   }
 
+  // -flang-deprecated-no-hlfir
+  if (args.hasArg(clang::driver::options::OPT_flang_deprecated_no_hlfir) &&
+      !args.hasArg(clang::driver::options::OPT_emit_hlfir)) {
+    if (args.hasArg(clang::driver::options::OPT_flang_experimental_hlfir)) {
+      const unsigned diagID = diags.getCustomDiagID(
+          clang::DiagnosticsEngine::Error,
+          "Options '-flang-experimental-hlfir' and "
+          "'-flang-deprecated-no-hlfir' cannot be both specified");
+      diags.Report(diagID);
+    }
+    res.loweringOpts.setLowerToHighLevelFIR(false);
+  }
+
   if (args.hasArg(clang::driver::options::OPT_flang_experimental_polymorphism)) {
     res.loweringOpts.setPolymorphicTypeImpl(true);
   }