[flang] Treat pre-processed input as fixed (#117563)

Fixes an issue introduced by

9fb2db1 [flang] Retain spaces when preprocessing fixed-form source

Where flang -fc1 fails to parse preprocessor output because it now
remains in fixed form.

Author: macurtis-amd

clang/lib/Driver/ToolChains/Flang.cpp

@@ -777,6 +777,13 @@ void Flang::ConstructJob(Compilation &C, const JobAction &JA,
 
   addFortranDialectOptions(Args, CmdArgs);
 
+  // 'flang -E' always produces output that is suitable for use as fixed form
+  // Fortran. However it is only valid free form source if the original is also
+  // free form.
+  if (InputType == types::TY_PP_Fortran &&
+      !Args.getLastArg(options::OPT_ffixed_form, options::OPT_ffree_form))
+    CmdArgs.push_back("-ffixed-form");
+
   handleColorDiagnosticsArgs(D, Args, CmdArgs);
 
   // LTO mode is parsed by the Clang driver library.

flang/test/Driver/pp-fixed-form.f90

@@ -0,0 +1,19 @@
+!RUN: %flang -save-temps -### %S/Inputs/free-form-test.f90  2>&1 | FileCheck %s --check-prefix=FREE
+FREE:       "-fc1" {{.*}} "-o" "free-form-test.i" {{.*}} "-x" "f95-cpp-input" "{{.*}}/free-form-test.f90"
+FREE-NEXT:  "-fc1" {{.*}} "-ffixed-form" {{.*}} "-x" "f95" "free-form-test.i"
+
+!RUN: %flang -save-temps -### %S/Inputs/fixed-form-test.f  2>&1 | FileCheck %s --check-prefix=FIXED
+FIXED:      "-fc1" {{.*}} "-o" "fixed-form-test.i" {{.*}} "-x" "f95-cpp-input" "{{.*}}/fixed-form-test.f"
+FIXED-NEXT: "-fc1" {{.*}} "-ffixed-form" {{.*}} "-x" "f95" "fixed-form-test.i"
+
+!RUN: %flang -save-temps -### -ffree-form %S/Inputs/free-form-test.f90  2>&1 | FileCheck %s --check-prefix=FREE-FLAG
+FREE-FLAG:           "-fc1" {{.*}} "-o" "free-form-test.i" {{.*}} "-x" "f95-cpp-input" "{{.*}}/free-form-test.f90"
+FREE-FLAG-NEXT:      "-fc1" {{.*}} "-emit-llvm-bc" "-ffree-form"
+FREE-FLAG-NOT:       "-ffixed-form"
+FREE-FLAG-SAME:      "-x" "f95" "free-form-test.i"
+
+!RUN: %flang -save-temps -### -ffixed-form %S/Inputs/fixed-form-test.f  2>&1 | FileCheck %s --check-prefix=FIXED-FLAG
+FIXED-FLAG:          "-fc1" {{.*}} "-o" "fixed-form-test.i" {{.*}} "-x" "f95-cpp-input" "{{.*}}/fixed-form-test.f"
+FIXED-FLAG-NEXT:     "-fc1" {{.*}} "-emit-llvm-bc" "-ffixed-form"
+FIXED-FLAG-NOT:      "-ffixed-form"
+FIXED-FLAG-SAME:     "-x" "f95" "fixed-form-test.i"