[flang] Finer control over warnings

Establish a set of optional usage warnings, and enable some
only in "-pedantic" mode that, in our subjective experience
with application codes, seem to issue frequently without
indicating usage that really needs to be corrected.  By default,
with this patch the compiler should appear to be somewhat less
persnickety but not less informative.

Differential Revision: https://reviews.llvm.org/D150710

flang/include/flang/Common/Fortran-features.h

@@ -16,6 +16,7 @@
 
 namespace Fortran::common {
 
+// Non-conforming extensions & legacies
 ENUM_CLASS(LanguageFeature, BackslashEscapes, OldDebugLines,
     FixedFormContinuationWithColumn1Ampersand, LogicalAbbreviations,
     XOROperator, PunctuationInNames, OptionalFreeFormSpace, BOZExtensions,
@@ -34,9 +35,17 @@ ENUM_CLASS(LanguageFeature, BackslashEscapes, OldDebugLines,
     ProgramReturn, ImplicitNoneTypeNever, ImplicitNoneTypeAlways,
     ForwardRefImplicitNone, OpenAccessAppend, BOZAsDefaultInteger,
     DistinguishableSpecifics, DefaultSave, PointerInSeqType, NonCharacterFormat,
-    SaveMainProgram, SaveBigMainProgramVariables)
+    SaveMainProgram, SaveBigMainProgramVariables,
+    DistinctArrayConstructorLengths)
+
+// Portability and suspicious usage warnings for conforming code
+ENUM_CLASS(UsageWarning, Portability, PointerToUndefinable,
+    NonTargetPassedToTarget, PointerToPossibleNoncontiguous,
+    ShortCharacterActual, ExprPassedToVolatile, ImplicitInterfaceActual,
+    PolymorphicTransferArg, PointerComponentTransferArg, TransferSizePresence)
 
 using LanguageFeatures = EnumSet<LanguageFeature, LanguageFeature_enumSize>;
+using UsageWarnings = EnumSet<UsageWarning, UsageWarning_enumSize>;
 
 class LanguageFeatureControl {
 public:
@@ -58,22 +67,33 @@ class LanguageFeatureControl {
   }
   LanguageFeatureControl(const LanguageFeatureControl &) = default;
   void Enable(LanguageFeature f, bool yes = true) { disable_.set(f, !yes); }
-  void EnableWarning(LanguageFeature f, bool yes = true) { warn_.set(f, yes); }
-  void WarnOnAllNonstandard(bool yes = true) { warnAll_ = yes; }
+  void EnableWarning(LanguageFeature f, bool yes = true) {
+    warnLanguage_.set(f, yes);
+  }
+  void EnableWarning(UsageWarning w, bool yes = true) {
+    warnUsage_.set(w, yes);
+  }
+  void WarnOnAllNonstandard(bool yes = true) { warnAllLanguage_ = yes; }
+  void WarnOnAllUsage(bool yes = true) { warnAllUsage_ = yes; }
   bool IsEnabled(LanguageFeature f) const { return !disable_.test(f); }
   bool ShouldWarn(LanguageFeature f) const {
-    return (warnAll_ && f != LanguageFeature::OpenMP &&
+    return (warnAllLanguage_ && f != LanguageFeature::OpenMP &&
                f != LanguageFeature::OpenACC) ||
-        warn_.test(f);
+        warnLanguage_.test(f);
+  }
+  bool ShouldWarn(UsageWarning w) const {
+    return warnAllUsage_ || warnUsage_.test(w);
   }
   // Return all spellings of operators names, depending on features enabled
   std::vector<const char *> GetNames(LogicalOperator) const;
   std::vector<const char *> GetNames(RelationalOperator) const;
 
 private:
   LanguageFeatures disable_;
-  LanguageFeatures warn_;
-  bool warnAll_{false};
+  LanguageFeatures warnLanguage_;
+  bool warnAllLanguage_{false};
+  UsageWarnings warnUsage_;
+  bool warnAllUsage_{false};
 };
 } // namespace Fortran::common
 #endif // FORTRAN_COMMON_FORTRAN_FEATURES_H_

flang/include/flang/Frontend/CompilerInvocation.h

@@ -106,6 +106,7 @@ class CompilerInvocation : public CompilerInvocationBase {
   Fortran::common::IntrinsicTypeDefaultKinds defaultKinds;
 
   bool enableConformanceChecks = false;
+  bool enableUsageChecks = false;
 
   /// Used in e.g. unparsing to dump the analyzed rather than the original
   /// parse-tree objects.
@@ -184,6 +185,9 @@ class CompilerInvocation : public CompilerInvocationBase {
     return enableConformanceChecks;
   }
 
+  bool &getEnableUsageChecks() { return enableUsageChecks; }
+  const bool &getEnableUsageChecks() const { return enableUsageChecks; }
+
   Fortran::parser::AnalyzedObjectsAsFortran &getAsFortran() {
     return asFortran;
   }
@@ -209,6 +213,9 @@ class CompilerInvocation : public CompilerInvocationBase {
   // Enables the std=f2018 conformance check
   void setEnableConformanceChecks() { enableConformanceChecks = true; }
 
+  // Enables the usage checks
+  void setEnableUsageChecks() { enableUsageChecks = true; }
+
   /// Useful setters
   void setModuleDir(std::string &dir) { moduleDir = dir; }
 

flang/include/flang/Semantics/semantics.h

@@ -81,8 +81,8 @@ class SemanticsContext {
   bool IsEnabled(common::LanguageFeature feature) const {
     return languageFeatures_.IsEnabled(feature);
   }
-  bool ShouldWarn(common::LanguageFeature feature) const {
-    return languageFeatures_.ShouldWarn(feature);
+  template <typename A> bool ShouldWarn(A x) const {
+    return languageFeatures_.ShouldWarn(x);
   }
   const std::optional<parser::CharBlock> &location() const { return location_; }
   const std::vector<std::string> &searchDirectories() const {
@@ -93,7 +93,6 @@ class SemanticsContext {
   }
   const std::string &moduleDirectory() const { return moduleDirectory_; }
   const std::string &moduleFileSuffix() const { return moduleFileSuffix_; }
-  bool warnOnNonstandardUsage() const { return warnOnNonstandardUsage_; }
   bool warningsAreErrors() const { return warningsAreErrors_; }
   bool debugModuleWriter() const { return debugModuleWriter_; }
   const evaluate::IntrinsicProcTable &intrinsics() const { return intrinsics_; }

flang/lib/Frontend/CompilerInvocation.cpp

@@ -774,8 +774,9 @@ static bool parseDialectArgs(CompilerInvocation &res, llvm::opt::ArgList &args,
   // -pedantic
   if (args.hasArg(clang::driver::options::OPT_pedantic)) {
     res.setEnableConformanceChecks();
+    res.setEnableUsageChecks();
   }
-  // -std=f2018 (currently this implies -pedantic)
+  // -std=f2018
   // TODO: Set proper options when more fortran standards
   // are supported.
   if (args.hasArg(clang::driver::options::OPT_std_EQ)) {
@@ -1045,9 +1046,11 @@ void CompilerInvocation::setFortranOpts() {
   if (frontendOptions.needProvenanceRangeToCharBlockMappings)
     fortranOptions.needProvenanceRangeToCharBlockMappings = true;
 
-  if (getEnableConformanceChecks()) {
+  if (getEnableConformanceChecks())
     fortranOptions.features.WarnOnAllNonstandard();
-  }
+
+  if (getEnableUsageChecks())
+    fortranOptions.features.WarnOnAllUsage();
 }
 
 void CompilerInvocation::setSemanticsOpts(
@@ -1060,7 +1063,6 @@ void CompilerInvocation::setSemanticsOpts(
   semanticsContext->set_moduleDirectory(getModuleDir())
       .set_searchDirectories(fortranOptions.searchDirectories)
       .set_intrinsicModuleDirectories(fortranOptions.intrinsicModuleDirectories)
-      .set_warnOnNonstandardUsage(getEnableConformanceChecks())
       .set_warningsAreErrors(getWarnAsErr())
       .set_moduleFileSuffix(getModuleFileSuffix());
 

flang/lib/Semantics/assignment.cpp

@@ -90,8 +90,7 @@ void AssignmentContext::Analyze(const parser::PointerAssignmentStmt &stmt) {
   if (const evaluate::Assignment * assignment{GetAssignment(stmt)}) {
     parser::CharBlock at{context_.location().value()};
     auto restorer{foldingContext().messages().SetLocation(at)};
-    CheckPointerAssignment(
-        foldingContext(), *assignment, context_.FindScope(at));
+    CheckPointerAssignment(context_, *assignment, context_.FindScope(at));
   }
 }