[flang][driver] Add forced form flags and -ffixed-line-length

Add support for the following layout options:
* -ffree-form
* -ffixed-form
- -ffixed-line-length=n (alias -ffixed-line-length-n)
Additionally remove options `-fno-free-form` and `-fno-fixed-form` as they were initially added to forward to gfortran but gfortran does not support these flags.

This patch adds the flag FlangOnlyOption to the existing options `-ffixed-form`, `-ffree-form` and `-ffree-line-length-` in Options.td. As of commit 6a75496836ea14bcfd2f4b59d35a1cad4ac58cee, these flags are not currently forwarded to gfortran anyway.

The default fixed line length in FrontendOptions is 72, based off the current default in Fortran::parser::Options. The line length cannot be set to a negative integer, or a positive integer less than 7 excluding 0, consistent with the behaviour of gfortran.

This patch does not add `-ffree-line-length-n` as Fortran::parser::Options does not have a variable for free form columns.
Whilst the `fixedFormColumns` variable is used in f18 for `-ffree-line-length-n`, f18 only allows `-ffree-line-length-none`/`-ffree-line-length-0` and not a user-specified value. `fixedFormcolumns` cannot be used in the new driver as it is ignored in the frontend when dealing with free form files.

Summary of changes:
- Remove -fno-fixed-form and -fno-free-form from Options.td
- Make -ffixed-form, -ffree-form and -ffree-line-length-n FlangOnlyOption in Options.td
- Create AddFortranDialectOptions method in Flang.cpp
- Create FortranForm enum in FrontendOptions.h
- Add fortranForm_ and fixedFormColumns_ to Fortran::frontend::FrontendOptions
- Update fixed-form-test.f so that it guarantees that it fails when forced as a free form file to better facilitate testing.

Differential Revision: https://reviews.llvm.org/D95460

1 files changed, 41 insertions, 0 deletions

diff --git a/flang/lib/Frontend/CompilerInvocation.cpp b/flang/lib/Frontend/CompilerInvocation.cpp
index 5077d06..563953f7 100644
--- a/flang/lib/Frontend/CompilerInvocation.cpp
+++ b/flang/lib/Frontend/CompilerInvocation.cpp
@@ -162,6 +162,40 @@ static InputKind ParseFrontendArgs(FrontendOptions &opts,
 
     opts.inputs_.emplace_back(std::move(inputs[i]), ik);
   }
+
+  // Set fortranForm_ based on options -ffree-form and -ffixed-form.
+  if (const auto *arg = args.getLastArg(clang::driver::options::OPT_ffixed_form,
+          clang::driver::options::OPT_ffree_form)) {
+    opts.fortranForm_ =
+        arg->getOption().matches(clang::driver::options::OPT_ffixed_form)
+        ? FortranForm::FixedForm
+        : FortranForm::FreeForm;
+  }
+
+  // Set fixedFormColumns_ based on -ffixed-line-length=<value>
+  if (const auto *arg =
+          args.getLastArg(clang::driver::options::OPT_ffixed_line_length_EQ)) {
+    llvm::StringRef argValue = llvm::StringRef(arg->getValue());
+    std::int64_t columns = -1;
+    if (argValue == "none") {
+      columns = 0;
+    } else if (argValue.getAsInteger(/*Radix=*/10, columns)) {
+      columns = -1;
+    }
+    if (columns < 0) {
+      diags.Report(clang::diag::err_drv_invalid_value_with_suggestion)
+          << arg->getOption().getName() << arg->getValue()
+          << "value must be 'none' or a non-negative integer";
+    } else if (columns == 0) {
+      opts.fixedFormColumns_ = 1000000;
+    } else if (columns < 7) {
+      diags.Report(clang::diag::err_drv_invalid_value_with_suggestion)
+          << arg->getOption().getName() << arg->getValue()
+          << "value must be at least seven";
+    } else {
+      opts.fixedFormColumns_ = columns;
+    }
+  }
   return dashX;
 }
 
@@ -278,8 +312,15 @@ void CompilerInvocation::SetDefaultFortranOpts() {
 
 void CompilerInvocation::setFortranOpts() {
   auto &fortranOptions = fortranOpts();
+  const auto &frontendOptions = frontendOpts();
   const auto &preprocessorOptions = preprocessorOpts();
 
+  if (frontendOptions.fortranForm_ != FortranForm::Unknown) {
+    fortranOptions.isFixedForm =
+        frontendOptions.fortranForm_ == FortranForm::FixedForm;
+  }
+  fortranOptions.fixedFormColumns = frontendOptions.fixedFormColumns_;
+
   collectMacroDefinitions(preprocessorOptions, fortranOptions);
 
   fortranOptions.searchDirectories.insert(