[clang][Interp] Fix failure to allocate local variables

We were incorrectly returning true when the allocateLocal() call
failed.

Author: tbaederr

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -2749,10 +2749,9 @@ bool ByteCodeExprGen<Emitter>::visitVarDecl(const VarDecl *VD) {
         return this->emitSetLocal(*VarT, Offset, VD);
       }
     } else {
-      if (std::optional<unsigned> Offset = this->allocateLocal(VD)) {
-        if (Init)
-          return this->visitLocalInitializer(Init, *Offset);
-      }
+      if (std::optional<unsigned> Offset = this->allocateLocal(VD))
+        return !Init || this->visitLocalInitializer(Init, *Offset);
+      return false;
     }
     return true;
   }

clang/test/AST/Interp/arrays.cpp

@@ -545,3 +545,22 @@ namespace LocalIndex {
     array[const_subscript] = 0;  // both-warning {{array index 3 is past the end of the array (that has type 'int[2]')}}
   }
 }
+
+namespace LocalVLA {
+  struct Foo {
+    int x;
+    Foo(int x) : x(x) {}
+  };
+  struct Elidable {
+    Elidable();
+  };
+
+  void foo(int size) {
+    Elidable elidableDynArray[size];
+#if __cplusplus >= 202002L
+     // both-note@-3 {{declared here}}
+     // both-warning@-3 {{variable length array}}
+     // both-note@-4 {{function parameter 'size' with unknown value}}
+#endif
+  }
+}