[Clang][Sema] Fix out-of-bounds access

Author: Sirraide

clang/lib/Sema/SemaOverload.cpp

@@ -7719,8 +7719,8 @@ bool Sema::CheckNonDependentConversions(
   unsigned Offset =
       Method && Method->hasCXXExplicitFunctionObjectParameter() ? 1 : 0;
 
-  for (unsigned I = 0, N = std::min(ParamTypes.size(), Args.size()); I != N;
-       ++I) {
+  for (unsigned I = 0, N = std::min(ParamTypes.size() - Offset, Args.size());
+       I != N; ++I) {
     QualType ParamType = ParamTypes[I + Offset];
     if (!ParamType->isDependentType()) {
       unsigned ConvIdx;

clang/test/SemaCXX/cxx2b-deducing-this.cpp

@@ -636,3 +636,13 @@ struct D {
     }
 };
 }
+
+namespace GH80971 {
+struct S {
+  auto f(this auto self...) {  }
+};
+
+int bug() {
+  S{}.f(0);
+}
+}