[flang-commits] [flang] [flang] Fix crash in error recovery (PR #92786)

[Peter Klausler via flang-commits]

https://github.com/klausler created https://github.com/llvm/llvm-project/pull/92786

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 https://github.com/llvm/llvm-project/issues/92636.

>From e32691881a0329b58e4d98e00ee0612f1d2a0979 Mon Sep 17 00:00:00 2001
From: Peter Klausler <pklausler at nvidia.com>
Date: Mon, 20 May 2024 09:29:43 -0700
Subject: [PATCH] [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 https://github.com/llvm/llvm-project/issues/92636.
---
 flang/include/flang/Semantics/symbol.h      |  1 +
 flang/lib/Semantics/resolve-names-utils.cpp | 44 +++++++++++++--------
 flang/lib/Semantics/resolve-names.cpp       |  2 +-
 flang/lib/Semantics/symbol.cpp              | 12 +++++-
 4 files changed, 39 insertions(+), 20 deletions(-)

diff --git a/flang/include/flang/Semantics/symbol.h b/flang/include/flang/Semantics/symbol.h
index 50f7b68d80cb1..f130036d949d7 100644
--- 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
index 3ca460b8e46ac..e27a54361749f 100644
--- 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
index a46c0f378d5d0..2622fa1e50747 100644
--- 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
index 381905b89fb2d..3eb120fd962fa 100644
--- 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 {