[flang] Fix crash in error recovery

EQUIVALENCE set processing assumes that any arrays have explicit shape and constant lower bounds. When an erroneous program violates those assumptions, the compiler crashes. Fix. Fixes #92636.
llvm · May 20, 2024 · e326918 · e326918
1 parent ab7930b
commit e326918
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Showing 4 changed files with 39 additions and 20 deletions.
diff --git a/flang/include/flang/Semantics/symbol.h b/flang/include/flang/Semantics/symbol.h
@@ -815,6 +815,7 @@ class Symbol {
   void SetIsExplicitBindName(bool);
   bool IsFuncResult() const;
   bool IsObjectArray() const;
+  const ArraySpec *GetShape() const;
   bool IsSubprogram() const;
   bool IsFromModFile() const;
   bool HasExplicitInterface() const {

diff --git a/flang/lib/Semantics/resolve-names-utils.cpp b/flang/lib/Semantics/resolve-names-utils.cpp
@@ -376,25 +376,35 @@ static void PropagateSaveAttr(const EquivalenceSet &src, EquivalenceSet &dst) {
 
 void EquivalenceSets::AddToSet(const parser::Designator &designator) {
   if (CheckDesignator(designator)) {
-    Symbol &symbol{*currObject_.symbol};
-    if (!currSet_.empty()) {
-      // check this symbol against first of set for compatibility
-      Symbol &first{currSet_.front().symbol};
-      CheckCanEquivalence(designator.source, first, symbol) &&
-          CheckCanEquivalence(designator.source, symbol, first);
-    }
-    auto subscripts{currObject_.subscripts};
-    if (subscripts.empty() && symbol.IsObjectArray()) {
-      // record a whole array as its first element
-      for (const ShapeSpec &spec : symbol.get<ObjectEntityDetails>().shape()) {
-        auto &lbound{spec.lbound().GetExplicit().value()};
-        subscripts.push_back(evaluate::ToInt64(lbound).value());
+    if (Symbol * symbol{currObject_.symbol}) {
+      if (!currSet_.empty()) {
+        // check this symbol against first of set for compatibility
+        Symbol &first{currSet_.front().symbol};
+        CheckCanEquivalence(designator.source, first, *symbol) &&
+            CheckCanEquivalence(designator.source, *symbol, first);
+      }
+      auto subscripts{currObject_.subscripts};
+      if (subscripts.empty()) {
+        if (const ArraySpec * shape{symbol->GetShape()};
+            shape && shape->IsExplicitShape()) {
+          // record a whole array as its first element
+          for (const ShapeSpec &spec : *shape) {
+            if (auto lbound{spec.lbound().GetExplicit()}) {
+              if (auto lbValue{evaluate::ToInt64(*lbound)}) {
+                subscripts.push_back(*lbValue);
+                continue;
+              }
+            }
+            subscripts.clear(); // error recovery
+            break;
+          }
+        }
       }
+      auto substringStart{currObject_.substringStart};
+      currSet_.emplace_back(
+          *symbol, subscripts, substringStart, designator.source);
+      PropagateSaveAttr(currSet_.back(), currSet_);
     }
-    auto substringStart{currObject_.substringStart};
-    currSet_.emplace_back(
-        symbol, subscripts, substringStart, designator.source);
-    PropagateSaveAttr(currSet_.back(), currSet_);
   }
   currObject_ = {};
 }

diff --git a/flang/lib/Semantics/resolve-names.cpp b/flang/lib/Semantics/resolve-names.cpp
@@ -6227,7 +6227,7 @@ void DeclarationVisitor::CheckEquivalenceSets() {
     }
     for (const parser::EquivalenceObject &object : *set) {
       const auto &designator{object.v.value()};
-      // The designator was not resolved when it was encountered so do it now.
+      // The designator was not resolved when it was encountered, so do it now.
       // AnalyzeExpr causes array sections to be changed to substrings as needed
       Walk(designator);
       if (AnalyzeExpr(context(), designator)) {

diff --git a/flang/lib/Semantics/symbol.cpp b/flang/lib/Semantics/symbol.cpp
@@ -385,9 +385,17 @@ bool Symbol::IsFuncResult() const {
       details_);
 }
 
+const ArraySpec *Symbol::GetShape() const {
+  if (const auto *details{std::get_if<ObjectEntityDetails>(&details_)}) {
+    return &details->shape();
+  } else {
+    return nullptr;
+  }
+}
+
 bool Symbol::IsObjectArray() const {
-  const auto *details{std::get_if<ObjectEntityDetails>(&details_)};
-  return details && details->IsArray();
+  const ArraySpec *shape{GetShape()};
+  return shape && !shape->empty();
 }
 
 bool Symbol::IsSubprogram() const {