match.pd: Avoid ICE with shifts [PR97979]

match.pd: Avoid ICE with shifts [PR97979]

My recent wide_int_binop changes caused ICE on this testcase.
The problem is that for shift where amount has MSB set now fails to optimize
into a constant (IMHO we should treat out of bounds shifts the same later),
but there is a precedent for that already - e.g. division by zero fails
to optimize into a constant too.  I think it is better if path isolation
checks for these UBs and does something the user chooses (__builtin_trap vs.
__builtin_unreachable, and either a deferred warning about the UB or
nothing).
This patch just doesn't optimize if int_const_binop failed.

2020-11-26  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/97979
	* match.pd ((X {&,^,|} C2) << C1 into (X << C1) {&,^,|} (C2 << C1)):
	Only optimize if int_const_binop returned non-NULL.

	* gcc.dg/pr97979.c: New test.
	* gcc.c-torture/compile/pr97979.c: New test.