[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.

Author: jeanPerier

clang/include/clang/Driver/Options.td

@@ -6218,6 +6218,10 @@ def flang_experimental_hlfir : Flag<["-"], "flang-experimental-hlfir">,
   Flags<[HelpHidden]>, Visibility<[FlangOption, FC1Option]>,
   HelpText<"Use HLFIR lowering (experimental)">;
 
+def flang_deprecated_no_hlfir : Flag<["-"], "flang-deprecated-no-hlfir">,
+  Flags<[HelpHidden]>, Visibility<[FlangOption, FC1Option]>,
+  HelpText<"Do not use HLFIR lowering (deprecated)">;
+
 def flang_experimental_polymorphism : Flag<["-"], "flang-experimental-polymorphism">,
   Flags<[HelpHidden]>, Visibility<[FlangOption, FC1Option]>,
   HelpText<"Enable Fortran 2003 polymorphism (experimental)">;

clang/lib/Driver/ToolChains/Flang.cpp

@@ -143,6 +143,7 @@ void Flang::addCodegenOptions(const ArgList &Args,
     CmdArgs.push_back("-fversion-loops-for-stride");
 
   Args.addAllArgs(CmdArgs, {options::OPT_flang_experimental_hlfir,
+                            options::OPT_flang_deprecated_no_hlfir,
                             options::OPT_flang_experimental_polymorphism,
                             options::OPT_fno_ppc_native_vec_elem_order,
                             options::OPT_fppc_native_vec_elem_order,

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);
   }

flang/test/Driver/driver-help-hidden.f90

@@ -49,6 +49,8 @@
 ! CHECK-NEXT: -fintegrated-as         Enable the integrated assembler
 ! CHECK-NEXT: -fintrinsic-modules-path <dir>
 ! CHECK-NEXT:                         Specify where to find the compiled intrinsic modules
+! CHECK-NEXT: -flang-deprecated-no-hlfir
+! CHECK-NEXT:                         Do not use HLFIR lowering (deprecated)
 ! CHECK-NEXT: -flang-experimental-hlfir
 ! CHECK-NEXT:                         Use HLFIR lowering (experimental)
 ! CHECK-NEXT: -flang-experimental-polymorphism

flang/test/Driver/frontend-forwarding.f90

@@ -18,6 +18,7 @@
 ! RUN:     -fversion-loops-for-stride \
 ! RUN:     -flang-experimental-polymorphism \
 ! RUN:     -flang-experimental-hlfir \
+! RUN:     -flang-deprecated-no-hlfir \
 ! RUN:     -fno-ppc-native-vector-element-order \
 ! RUN:     -fppc-native-vector-element-order \
 ! RUN:     -mllvm -print-before-all \
@@ -49,6 +50,7 @@
 ! CHECK: "-fversion-loops-for-stride"
 ! CHECK: "-flang-experimental-polymorphism"
 ! CHECK: "-flang-experimental-hlfir"
+! CHECK: "-flang-deprecated-no-hlfir"
 ! CHECK: "-fno-ppc-native-vector-element-order"
 ! CHECK: "-fppc-native-vector-element-order"
 ! CHECK: "-Rpass"

flang/test/Driver/hlfir-no-hlfir-error.f90

@@ -0,0 +1,16 @@
+! Test that -flang-experimental-hlfir and -flang-deprecated-no-hlfir
+! options cannot be both used.
+
+!--------------------------
+! FLANG DRIVER (flang-new)
+!--------------------------
+! RUN: not %flang -flang-experimental-hlfir -flang-deprecated-no-hlfir %s 2>&1 | FileCheck %s
+
+!-----------------------------------------
+! FRONTEND FLANG DRIVER (flang-new -fc1)
+!-----------------------------------------
+! RUN: not %flang_fc1 -emit-llvm -flang-experimental-hlfir -flang-deprecated-no-hlfir %s 2>&1 | FileCheck %s
+
+! CHECK:error: Options '-flang-experimental-hlfir' and '-flang-deprecated-no-hlfir' cannot be both specified
+
+end

flang/test/HLFIR/hlfir-flags.f90

@@ -4,6 +4,7 @@
 ! RUN: %flang_fc1 -emit-hlfir -flang-experimental-hlfir -o - %s | FileCheck --check-prefix HLFIR --check-prefix ALL %s
 ! RUN: bbc -emit-hlfir -hlfir -o - %s | FileCheck --check-prefix HLFIR --check-prefix ALL %s
 ! RUN: %flang_fc1 -emit-fir -o - %s | FileCheck %s --check-prefix NO-HLFIR --check-prefix ALL
+! RUN: %flang_fc1 -emit-fir -flang-deprecated-no-hlfir -o - %s | FileCheck %s --check-prefix NO-HLFIR --check-prefix ALL
 ! RUN: bbc -emit-fir -o - %s | FileCheck %s --check-prefix NO-HLFIR --check-prefix ALL
 ! RUN: %flang_fc1 -emit-fir -flang-experimental-hlfir -o - %s | FileCheck --check-prefix FIR --check-prefix ALL %s
 ! RUN: bbc -emit-fir -hlfir -o - %s | FileCheck --check-prefix FIR --check-prefix ALL %s