[clang][bytecode] Create local scopes for if then/else statements (#120852)

In case those aren't compound statements.

Author: tbaederr

clang/lib/AST/ByteCode/Compiler.cpp

@@ -4974,20 +4974,35 @@ template <class Emitter> bool Compiler<Emitter>::visitIfStmt(const IfStmt *IS) {
     LabelTy LabelEnd = this->getLabel();
     if (!this->jumpFalse(LabelElse))
       return false;
-    if (!visitStmt(IS->getThen()))
-      return false;
+    {
+      LocalScope<Emitter> ThenScope(this);
+      if (!visitStmt(IS->getThen()))
+        return false;
+      if (!ThenScope.destroyLocals())
+        return false;
+    }
     if (!this->jump(LabelEnd))
       return false;
     this->emitLabel(LabelElse);
-    if (!visitStmt(Else))
-      return false;
+    {
+      LocalScope<Emitter> ElseScope(this);
+      if (!visitStmt(Else))
+        return false;
+      if (!ElseScope.destroyLocals())
+        return false;
+    }
     this->emitLabel(LabelEnd);
   } else {
     LabelTy LabelEnd = this->getLabel();
     if (!this->jumpFalse(LabelEnd))
       return false;
-    if (!visitStmt(IS->getThen()))
-      return false;
+    {
+      LocalScope<Emitter> ThenScope(this);
+      if (!visitStmt(IS->getThen()))
+        return false;
+      if (!ThenScope.destroyLocals())
+        return false;
+    }
     this->emitLabel(LabelEnd);
   }
 

clang/test/AST/ByteCode/if.cpp

@@ -76,3 +76,30 @@ namespace IfScope {
   }
   static_assert(foo() == 13, "");
 }
+
+namespace IfScope2 {
+  struct __bit_iterator {
+    unsigned __ctz_;
+  };
+  constexpr void __fill_n_bool(__bit_iterator) {}
+
+  constexpr void fill_n(__bit_iterator __first) {
+    if (false)
+      __fill_n_bool(__first);
+    else
+      __fill_n_bool(__first);
+  }
+
+  struct bitset{
+    constexpr void reset() {
+      auto m = __bit_iterator(8);
+      fill_n(m);
+    }
+  };
+  consteval bool foo() {
+    bitset v;
+    v.reset();
+    return true;
+  }
+  static_assert(foo());
+}