[flang-commits] [flang] [flang] Accept C-style comments in label fields (PR #207012)

[Leandro Lupori via flang-commits]

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@@ -83,13 +83,21 @@ bool FrontendAction::beginSourceFile(CompilerInstance &ci,
   //  * `-cpp/-nocpp`, or
   //  * the file extension (if the user didn't express any preference)
   // to decide whether to include them or not.
-  if ((invoc.getPreprocessorOpts().macrosFlag == PPMacrosFlag::Include) ||
+  bool includeMacros =
+      (invoc.getPreprocessorOpts().macrosFlag == PPMacrosFlag::Include) ||
       (invoc.getPreprocessorOpts().showMacros) ||
       (invoc.getPreprocessorOpts().macrosFlag == PPMacrosFlag::Unknown &&
-       getCurrentInput().getMustBePreprocessed())) {
+       getCurrentInput().getMustBePreprocessed());
+  if (includeMacros) {
     invoc.setDefaultPredefinitions();
     invoc.collectMacroDefinitions();
   }
+  // Preprocessing is enabled if macros are included or if `-E` is specified
+  // and `-nocpp` is not.
+  invoc.getFortranOpts().preprocessingEnabled =
----------------
luporl wrote:

It seemed to me that `-E` should imply `preprocessingEnabled`, but I had not considered the `-save-temps` pipeline. To avoid introducing asymmetries or adding complexity to the frontend I reverted that change.

For reference, this is the behavior of other compilers:
- gfortran -E: `error: gfortran does not support -E without -cpp`
- ifx -E: always accepts C-style comments, independent of the `-fpp` and `-nofpp` flags.


https://github.com/llvm/llvm-project/pull/207012