[flang-commits] [PATCH] D143776: [flang] Warn about construct names that are not distinct in the inclusive scope

[Peter Klausler via Phabricator via flang-commits]

klausler created this revision.
klausler added a reviewer: vdonaldson.
klausler added a project: Flang.
Herald added subscribers: sunshaoce, jdoerfert.
Herald added a reviewer: clementval.
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klausler requested review of this revision.

f18 implements BLOCK scoping for construct names, like most but not all Fortran
compilers, but in the 2018 standard such names are defined to be local identifiers
whose scope is the inclusive scope -- i.e., the subprogram or main program.
Detect usage that depends on this extension and emit a portability warning.


https://reviews.llvm.org/D143776

Files:
  flang/docs/Extensions.md
  flang/lib/Semantics/resolve-names.cpp
  flang/test/Semantics/OpenACC/acc-branch.f90


Index: flang/test/Semantics/OpenACC/acc-branch.f90
===================================================================
--- flang/test/Semantics/OpenACC/acc-branch.f90
+++ flang/test/Semantics/OpenACC/acc-branch.f90
@@ -53,6 +53,7 @@
   ! Exit branches out of parallel construct, attached to an OpenACC parallel construct.
   thisblk: BLOCK
     fortname: if (.true.) then
+      !PORTABILITY: The construct name 'name1' should be distinct at the subprogram level
       name1: do k = 1, N
         !$acc parallel
         !ERROR: EXIT to construct 'fortname' outside of PARALLEL construct is not allowed
Index: flang/lib/Semantics/resolve-names.cpp
===================================================================
--- flang/lib/Semantics/resolve-names.cpp
+++ flang/lib/Semantics/resolve-names.cpp
@@ -553,6 +553,7 @@
   // Search for name in a derived type scope and its parents.
   Symbol *FindInTypeOrParents(const Scope &, const parser::Name &);
   Symbol *FindInTypeOrParents(const parser::Name &);
+  Symbol *FindInScopeOrBlockConstructs(const Scope &, SourceName);
   Symbol *FindSeparateModuleProcedureInterface(const parser::Name &);
   void EraseSymbol(const parser::Name &);
   void EraseSymbol(const Symbol &symbol) { currScope().erase(symbol.name()); }
@@ -2369,6 +2370,20 @@
 Symbol *ScopeHandler::FindInTypeOrParents(const parser::Name &name) {
   return FindInTypeOrParents(currScope(), name);
 }
+Symbol *ScopeHandler::FindInScopeOrBlockConstructs(
+    const Scope &scope, SourceName name) {
+  if (Symbol * symbol{FindInScope(scope, name)}) {
+    return symbol;
+  }
+  for (const Scope &child : scope.children()) {
+    if (child.kind() == Scope::Kind::BlockConstruct) {
+      if (Symbol * symbol{FindInScopeOrBlockConstructs(child, name)}) {
+        return symbol;
+      }
+    }
+  }
+  return nullptr;
+}
 
 void ScopeHandler::EraseSymbol(const parser::Name &name) {
   currScope().erase(name.source);
@@ -6556,8 +6571,19 @@
 }
 
 bool ConstructVisitor::CheckDef(const std::optional<parser::Name> &x) {
-  if (x) {
-    MakeSymbol(*x, MiscDetails{MiscDetails::Kind::ConstructName});
+  if (x && !x->symbol) {
+    // Construct names are not scoped by BLOCK in the standard, but many,
+    // but not all, compilers do treat them as if they were so scoped.
+    if (Symbol * inner{FindInScope(currScope(), *x)}) {
+      SayAlreadyDeclared(*x, *inner);
+    } else {
+      if (Symbol *
+          other{FindInScopeOrBlockConstructs(InclusiveScope(), x->source)}) {
+        SayWithDecl(*x, *other,
+            "The construct name '%s' should be distinct at the subprogram level"_port_en_US);
+      }
+      MakeSymbol(*x, MiscDetails{MiscDetails::Kind::ConstructName});
+    }
   }
   return true;
 }
Index: flang/docs/Extensions.md
===================================================================
--- flang/docs/Extensions.md
+++ flang/docs/Extensions.md
@@ -79,6 +79,11 @@
   kind 4, because the grammar of Fortran expressions parses it as a
   negation of a literal constant, not a negative literal constant.
   This compiler accepts it with a portability warning.
+* Construct names like `loop` in `loop: do j=1,n` are defined to
+  be "local identifiers" and should be distinct in the "inclusive
+  scope" -- i.e., not scoped by `BLOCK` constructs.
+  As most (but not all) compilers implement `BLOCK` scoping of construct
+  names, so does f18, with a portability warning.
 
 ## Extensions, deletions, and legacy features supported by default
 


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