[clang] [clang][OpenMP] Diagnose badly-formed collapsed imperfect loop nests (#60678) (PR #101305)

[Alexey Bataev via cfe-commits]

================
@@ -7668,6 +7669,47 @@ struct LoopIterationSpace final {
   Expr *FinalCondition = nullptr;
 };
 
+class ForSubExprChecker : public RecursiveASTVisitor<ForSubExprChecker> {
+  const llvm::SmallSet<Decl *, 4> *CollapsedLoopVarDecls;
+  VarDecl *ForbiddenVar;
+  SourceRange ErrLoc;
+
+public:
+  explicit ForSubExprChecker(
+      const llvm::SmallSet<Decl *, 4> *CollapsedLoopVarDecls)
+      : CollapsedLoopVarDecls(CollapsedLoopVarDecls), ForbiddenVar(nullptr) {}
+
+  bool shouldVisitImplicitCode() const { return true; }
+
+  bool VisitDeclRefExpr(DeclRefExpr *E) {
+    ValueDecl *VD = E->getDecl();
+    if (!isa<VarDecl, BindingDecl>(VD))
+      return true;
+    VarDecl *V = VD->getPotentiallyDecomposedVarDecl();
+    if (V->getType()->isReferenceType()) {
+      VarDecl *VD = V->getDefinition();
+      if (VD->hasInit()) {
+        Expr *I = VD->getInit();
+        DeclRefExpr *DRE = dyn_cast<DeclRefExpr>(I);
+        if (!DRE)
+          return true;
+        V = DRE->getDecl()->getPotentiallyDecomposedVarDecl();
+      }
+    }
+    Decl *Canon = V->getCanonicalDecl();
+    if (CollapsedLoopVarDecls->contains(Canon)) {
+      ForbiddenVar = V;
+      ErrLoc = E->getSourceRange();
+      return false;
+    }
+
+    return true;
+  }
+
+  VarDecl *getForbiddenVar() { return ForbiddenVar; }
+  SourceRange &getErrRange() { return ErrLoc; }
----------------
alexey-bataev wrote:

const functions

https://github.com/llvm/llvm-project/pull/101305