When determining if a constraint is satisfied, the function satisfy_argument_deduction_constraint temporarily changes the PLACEHOLDER_TYPE_CONSTRAINTS of an tree node. Since PLACEHOLDER_TYPE_CONSTRAINTS are taken into account when determining the equality of two types, this means that the node's canonical type must also change; otherwise, an ICE results if the type is compared to another type that it was previously equal to.
The attached patch sets the node's TYPE_CANONICAL field to NULL_TREE
after the PLACEHOLDER_TYPE_CONSTRAINTS are changed and restores
TYPE_CANONICAL to its original value when the
PLACEHOLDER_TYPE_CONSTRAINTS value are changed back so that erroneous
canonical type comparisons aren't made.
Bootstrapped and regression tested on x86_64-linux
2015-12-03 Ryan Burn <cont...@rnburn.com>
PR c++/68683
* constraint.cc (satisfy_argument_deduction_constraint): Set
TYPE_CANONICAL to NULL_TREE if PLACEHOLDER_TYPE_CONSTRAINTS are
changed.
* g++.dg/concepts/pr68683.C: New test
pr68683.patch
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