clang c++ "infinite" loop with template class and operator->

[efriedma-quic]

Bugzilla Link	9619
Resolution	FIXED
Resolved on	Apr 09, 2014 02:36
Version	unspecified
OS	Linux
CC	@DougGregor,@zygoloid,@rjmccall

Extended Description

Testcase:
template struct A {
A<x+1> operator->() { return A<x+1>(); }
};
void f() { A<0> x; x->foo(); }

There isn't any limit on the number of operator->'s that clang will try to use.

[llvmbot]

What do you think should happen, out of interest?

[llvmbot]

Eli, did you try -ftemplate-depth to restrict the instantiation depth for templates? Normally, this value is set to 1024, so clang might take a while before stopping.

[efriedma-quic]

Setting the instantiation depth doesn't help... the templates are getting instantiated by the operator-> loop.

[llvmbot]

truncated call graph of hanging clang

[llvmbot]

Well, after about five minutes at 100% CPU and close to 100MB used RAM clang crashed. Before it crashed, I sampled it using Activity Monitor, and got the attached call graph (I truncated it, since it repeated more or less infinitely).

I don't really understand why DenseMap::grow is contained in the call graph, but other than that, it seems that clang creates an AST with an ArraySubscriptExpr node whose Base is itself. Then, when calling ArraySubscriptExpr::getExprLoc, it recurses with no end in sight.

[efriedma-quic]

*** Bug llvm/llvm-bugzilla-archive#9678 has been marked as a duplicate of this bug. ***

[efriedma-quic]

*** Bug llvm/llvm-bugzilla-archive#12259 has been marked as a duplicate of this bug. ***

[llvmbot]

The option -foperator-arrow-depth=N implemented in r194161 takes care of this.

[efriedma-quic]

mentioned in issue llvm/llvm-bugzilla-archive#9678