[flang][OpenMP] Fix crash on DECLARE REDUCTION in unparse-with-symbols (llvm#157871)

Author: kparzysz

flang/lib/Semantics/unparse-with-symbols.cpp

@@ -37,6 +37,8 @@ class SymbolDumpVisitor {
   template <typename T> void Post(const parser::Statement<T> &) {
     currStmt_ = std::nullopt;
   }
+  void Post(const parser::Name &name);
+
   bool Pre(const parser::AccClause &clause) {
     currStmt_ = clause.source;
     return true;
@@ -57,7 +59,6 @@ class SymbolDumpVisitor {
     return true;
   }
   void Post(const parser::OpenMPThreadprivate &) { currStmt_ = std::nullopt; }
-  void Post(const parser::Name &name);
 
   bool Pre(const parser::OpenMPDeclareMapperConstruct &x) {
     currStmt_ = x.source;
@@ -67,6 +68,14 @@ class SymbolDumpVisitor {
     currStmt_ = std::nullopt;
   }
 
+  bool Pre(const parser::OpenMPDeclareReductionConstruct &x) {
+    currStmt_ = x.source;
+    return true;
+  }
+  void Post(const parser::OpenMPDeclareReductionConstruct &) {
+    currStmt_ = std::nullopt;
+  }
+
   bool Pre(const parser::OpenMPDeclareTargetConstruct &x) {
     currStmt_ = x.source;
     return true;
@@ -120,6 +129,7 @@ void SymbolDumpVisitor::Indent(llvm::raw_ostream &out, int indent) const {
 void SymbolDumpVisitor::Post(const parser::Name &name) {
   if (const auto *symbol{name.symbol}) {
     if (!symbol->has<MiscDetails>()) {
+      CHECK(currStmt_.has_value());
       symbols_.emplace(currStmt_.value().begin(), symbol);
     }
   }

flang/test/Parser/OpenMP/declare-reduction-unparse-with-symbols.f90

@@ -0,0 +1,13 @@
+!RUN: %flang_fc1 -fdebug-unparse-with-symbols -fopenmp %s | FileCheck %s
+
+! This used to crash.
+
+subroutine f00
+  !$omp declare reduction(fred : integer, real : omp_out = omp_in + omp_out)
+end
+
+!CHECK: !DEF: /f00 (Subroutine) Subprogram
+!CHECK: subroutine f00
+!CHECK: !$omp declare reduction (fred:integer,real:omp_out = omp_in+omp_out)
+!CHECK: end subroutine
+