Comments, Visited set with assert to make sure no recursion exists in the expression

Author: JanekvO

llvm/lib/Target/AMDGPU/AMDGPUMCResourceInfo.cpp

@@ -91,8 +91,17 @@ MCSymbol *MCResourceInfo::getMaxSGPRSymbol(MCContext &OutContext) {
   return OutContext.getOrCreateSymbol("amdgpu.max_num_sgpr");
 }
 
+// The (partially complete) expression should have no recursion in it. After
+// all, we're trying to avoid recursion using this codepath.
 static bool findSymbolInExpr(MCSymbol *Sym, const MCExpr *Expr,
-                             SmallVectorImpl<const MCExpr *> &Exprs) {
+                             SmallVectorImpl<const MCExpr *> &Exprs,
+                             SmallPtrSetImpl<const MCExpr *> &Visited) {
+  // Assert if any of the expressions is already visited (i.e., there is
+  // existing recursion).
+  assert(!Visited.contains(Expr) &&
+         "Expr should not exist in Visited as we're avoiding recursion");
+  Visited.insert(Expr);
+
   switch (Expr->getKind()) {
   default:
     return false;
@@ -107,17 +116,17 @@ static bool findSymbolInExpr(MCSymbol *Sym, const MCExpr *Expr,
   }
   case MCExpr::ExprKind::Binary: {
     const MCBinaryExpr *BExpr = cast<MCBinaryExpr>(Expr);
-    return findSymbolInExpr(Sym, BExpr->getLHS(), Exprs) ||
-           findSymbolInExpr(Sym, BExpr->getRHS(), Exprs);
+    return findSymbolInExpr(Sym, BExpr->getLHS(), Exprs, Visited) ||
+           findSymbolInExpr(Sym, BExpr->getRHS(), Exprs, Visited);
   }
   case MCExpr::ExprKind::Unary: {
     const MCUnaryExpr *UExpr = cast<MCUnaryExpr>(Expr);
-    return findSymbolInExpr(Sym, UExpr->getSubExpr(), Exprs);
+    return findSymbolInExpr(Sym, UExpr->getSubExpr(), Exprs, Visited);
   }
   case MCExpr::ExprKind::Target: {
     const AMDGPUMCExpr *AGVK = cast<AMDGPUMCExpr>(Expr);
     for (const MCExpr *E : AGVK->getArgs()) {
-      if (findSymbolInExpr(Sym, E, Exprs))
+      if (findSymbolInExpr(Sym, E, Exprs, Visited))
         return true;
     }
     return false;
@@ -132,11 +141,12 @@ static bool findSymbolInExpr(MCSymbol *Sym, const MCExpr *Expr,
 // contains the symbol Expr is associated with.
 static bool foundRecursiveSymbolDef(MCSymbol *Sym, const MCExpr *Expr) {
   SmallVector<const MCExpr *, 8> WorkList;
+  SmallPtrSet<const MCExpr *, 8> Visited;
   WorkList.push_back(Expr);
 
   while (!WorkList.empty()) {
     const MCExpr *CurExpr = WorkList.pop_back_val();
-    if (findSymbolInExpr(Sym, CurExpr, WorkList))
+    if (findSymbolInExpr(Sym, CurExpr, WorkList, Visited))
       return true;
   }