Segmentation fault on gcc caused by lambda wrapper over variadic template function call

Question

I\'ve spent quite a few hours today trying to understand why this code segfaults on g++6.2 and g++7.0, while happily working as intended on clang

Answer 1

This has nothing to do with temporaries: it's a gcc7.0 optimizer bug. This is a simpler reproducer:

#include 

struct root
{
  template 
  void start(TNode n, TNodes... ns)
  {
    n->execute(ns...);
  }
};

template 
struct node_then
{
  TParent *_p;

  node_then(TParent *p) : _p{ p }
  {
  }

  auto execute()
  {
  }

  template 
  auto execute(TNode n, TNodes... ns)
  {
    n->execute(ns...);
  }

  template 
  auto start(TNodes... ns)
  {
    _p->start(this, ns...);
  }
};

template 
struct node_wait_all
{
  TParent *_p;

  node_wait_all(TParent *p) : _p{ p }
  {
  }

  template 
  auto execute(TNode n, TNodes... ns)
  {
    ([&] { ([&] { n->execute(ns...); })(); })();
  }

  template 
  auto start(TNodes... ns)
  {
    _p->start(this, ns...);
  }
};


int main()
{
  //node_wait_all obj(new root());
  //node_then> obj2(new node_wait_all(new root()));
  node_then>> obj3(new node_then>(new node_wait_all(new root())));
  obj3.start();
}

Output:

prog.cc: In function 'int main()':
prog.cc:67:1: internal compiler error: in visit_ref_for_mod_analysis, at ipa-prop.c:2308
 }
 ^
0x96c4d6 visit_ref_for_mod_analysis
    /home/heads/gcc/gcc-source/gcc/ipa-prop.c:2308
0x8f615d walk_stmt_load_store_addr_ops(gimple*, void*, bool (*)(gimple*, tree_node*, tree_node*, void*), bool (*)(gimple*, tree_node*, tree_node*, void*), bool (*)(gimple*, tree_node*, tree_node*, void*))
    /home/heads/gcc/gcc-source/gcc/gimple-walk.c:817
0x9761a2 ipa_analyze_params_uses_in_bb
    /home/heads/gcc/gcc-source/gcc/ipa-prop.c:2335
0x9761a2 analysis_dom_walker::before_dom_children(basic_block_def*)
    /home/heads/gcc/gcc-source/gcc/ipa-prop.c:2415
0x10c8472 dom_walker::walk(basic_block_def*)
    /home/heads/gcc/gcc-source/gcc/domwalk.c:265
0x977ceb ipa_analyze_node(cgraph_node*)
    /home/heads/gcc/gcc-source/gcc/ipa-prop.c:2486
0x1108f0a ipcp_generate_summary
    /home/heads/gcc/gcc-source/gcc/ipa-cp.c:5036
0xa4759c execute_ipa_summary_passes(ipa_opt_pass_d*)
    /home/heads/gcc/gcc-source/gcc/passes.c:2167
0x7d6b45 ipa_passes
    /home/heads/gcc/gcc-source/gcc/cgraphunit.c:2311
0x7d6b45 symbol_table::compile()
    /home/heads/gcc/gcc-source/gcc/cgraphunit.c:2425
0x7d8616 symbol_table::compile()
    /home/heads/gcc/gcc-source/gcc/cgraphunit.c:2587
0x7d8616 symbol_table::finalize_compilation_unit()
    /home/heads/gcc/gcc-source/gcc/cgraphunit.c:2584
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Link: http://melpon.org/wandbox/permlink/E11fOumFJda6OW6m

To aid in this code's comprehension I'm using a powerful debugging tool: paint.exe