https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100828
Bug ID: 100828
Summary: Arbitrary limit on constraint complexity
Product: gcc
Version: 11.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: matthewjbarichello at gmail dot com
Target Milestone: ---
Created attachment 50889
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50889&action=edit
Patch to remove the constraint complexity limit from gcc-11.1.0
It would seem that there is an arbitrary limit on the complexity of constraints
in gcc 11.
#define a (0 || 0 && 0)
namespace e {
template<typename>
struct f;
}
template<typename g>
concept f = e::f<g>::h && true && a;
template<typename>
concept i = a && a;
template <typename, typename j>
requires(i<j> || f<j>)
struct k;
template<typename g, typename j>
requires(i<j> && i<g>)
struct k<g, j>;
This example, reduced with c-reduce, yields:
<source>:19:8: error: ‘0 \/ 0 /\ 0 /\ 0 \/ 0 /\ 0 \/ e::f<
<template-parameter-1-1> >::h [with g = j] /\ true /\ 0 \/ 0 /\ 0’ exceeds the
maximum constraint complexity
19 | struct k<g, j>;
| ^~~~~~~
Attached is a patch for gcc, as of the releases/gcc-11.1.0 tag, which allows
gcc to compile the example without an issue.
Clang does not seem to have this limitation and has no problem compiling the
example. Is there a reason for this limit?
