[flang] Fix references to destroyed objects (llvm#111582)

ProgramTree instances are created as the value of a local variable in
the Pre(const parser::ProgramUnit &) member function in name resolution.
But references to these ProgramTree instances can persist in
SubprogramNameDetails symbol table entries that might survive that
function call's lifetime, and lead to trouble later when (e.g.)
expression semantics needs to deal with a possible forward reference in
a function reference in an expression being processed later in
expression checking.

So put those ProgramTree instances into a longer-lived linked list
within the SemanticsContext.

Might fix some weird crashes reported on big-endian targets (AIX &
Solaris).

Author: klausler

flang/lib/Semantics/program-tree.h renamed to flang/include/flang/Semantics/program-tree.h

@@ -9,8 +9,8 @@
 #ifndef FORTRAN_SEMANTICS_PROGRAM_TREE_H_
 #define FORTRAN_SEMANTICS_PROGRAM_TREE_H_
 
+#include "symbol.h"
 #include "flang/Parser/parse-tree.h"
-#include "flang/Semantics/symbol.h"
 #include <list>
 #include <variant>
 
@@ -35,7 +35,7 @@ class ProgramTree {
       std::list<common::Reference<const parser::GenericSpec>>;
 
   // Build the ProgramTree rooted at one of these program units.
-  static ProgramTree Build(const parser::ProgramUnit &, SemanticsContext &);
+  static ProgramTree &Build(const parser::ProgramUnit &, SemanticsContext &);
   static std::optional<ProgramTree> Build(
       const parser::MainProgram &, SemanticsContext &);
   static std::optional<ProgramTree> Build(

flang/include/flang/Semantics/semantics.h

@@ -9,6 +9,8 @@
 #ifndef FORTRAN_SEMANTICS_SEMANTICS_H_
 #define FORTRAN_SEMANTICS_SEMANTICS_H_
 
+#include "module-dependences.h"
+#include "program-tree.h"
 #include "scope.h"
 #include "symbol.h"
 #include "flang/Common/Fortran-features.h"
@@ -17,7 +19,6 @@
 #include "flang/Evaluate/intrinsics.h"
 #include "flang/Evaluate/target.h"
 #include "flang/Parser/message.h"
-#include "flang/Semantics/module-dependences.h"
 #include <iosfwd>
 #include <set>
 #include <string>
@@ -280,6 +281,9 @@ class SemanticsContext {
 
   void DumpSymbols(llvm::raw_ostream &);
 
+  // Top-level ProgramTrees are owned by the SemanticsContext for persistence.
+  ProgramTree &SaveProgramTree(ProgramTree &&);
+
 private:
   struct ScopeIndexComparator {
     bool operator()(parser::CharBlock, parser::CharBlock) const;
@@ -331,6 +335,7 @@ class SemanticsContext {
   ModuleDependences moduleDependences_;
   std::map<const Symbol *, SourceName> moduleFileOutputRenamings_;
   UnorderedSymbolSet isDefined_;
+  std::list<ProgramTree> programTrees_;
 };
 
 class Semantics {

flang/lib/Semantics/program-tree.cpp

@@ -6,7 +6,7 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "program-tree.h"
+#include "flang/Semantics/program-tree.h"
 #include "flang/Common/idioms.h"
 #include "flang/Parser/char-block.h"
 #include "flang/Semantics/scope.h"
@@ -130,13 +130,13 @@ static ProgramTree BuildModuleTree(
   return node;
 }
 
-ProgramTree ProgramTree::Build(
+ProgramTree &ProgramTree::Build(
     const parser::ProgramUnit &x, SemanticsContext &context) {
   return common::visit(
-      [&](const auto &y) {
+      [&](const auto &y) -> ProgramTree & {
         auto node{Build(y.value(), context)};
         CHECK(node.has_value());
-        return std::move(*node);
+        return context.SaveProgramTree(std::move(*node));
       },
       x.u);
 }

flang/lib/Semantics/resolve-names.cpp

@@ -10,7 +10,6 @@
 #include "definable.h"
 #include "mod-file.h"
 #include "pointer-assignment.h"
-#include "program-tree.h"
 #include "resolve-directives.h"
 #include "resolve-names-utils.h"
 #include "rewrite-parse-tree.h"
@@ -32,6 +31,7 @@
 #include "flang/Parser/tools.h"
 #include "flang/Semantics/attr.h"
 #include "flang/Semantics/expression.h"
+#include "flang/Semantics/program-tree.h"
 #include "flang/Semantics/scope.h"
 #include "flang/Semantics/semantics.h"
 #include "flang/Semantics/symbol.h"
@@ -2490,6 +2490,7 @@ Symbol &ScopeHandler::CopySymbol(const SourceName &name, const Symbol &symbol) {
 }
 
 // Look for name only in scope, not in enclosing scopes.
+
 Symbol *ScopeHandler::FindInScope(
     const Scope &scope, const parser::Name &name) {
   return Resolve(name, FindInScope(scope, name.source));
@@ -9120,7 +9121,7 @@ bool ResolveNamesVisitor::Pre(const parser::ProgramUnit &x) {
     ResolveAccParts(context(), x, &topScope_);
     return false;
   }
-  auto root{ProgramTree::Build(x, context())};
+  ProgramTree &root{ProgramTree::Build(x, context())};
   SetScope(topScope_);
   ResolveSpecificationParts(root);
   FinishSpecificationParts(root);

flang/lib/Semantics/semantics.cpp

@@ -663,6 +663,10 @@ void SemanticsContext::DumpSymbols(llvm::raw_ostream &os) {
   DoDumpSymbols(os, globalScope());
 }
 
+ProgramTree &SemanticsContext::SaveProgramTree(ProgramTree &&tree) {
+  return programTrees_.emplace_back(std::move(tree));
+}
+
 void Semantics::DumpSymbols(llvm::raw_ostream &os) { context_.DumpSymbols(os); }
 
 void Semantics::DumpSymbolsSources(llvm::raw_ostream &os) const {