match.pd: Don't optimize vector X + (X << C) -> X * (1 + (1 << C)) if there is no...

match.pd: Don't optimize vector X + (X << C) -> X * (1 + (1 << C)) if there is no mult support [PR99544]

E.g. on aarch64, the target has V2DImode addition and shift by scalar
optabs, but doesn't have V2DImode multiply.  The following testcase
ICEs because this simplification is done after last lowering, but
generally, even if it is done before that, turning it into a multiplication
will not be an improvement because that means scalarization, while the former
can be done in vectors.

It would be nice if we added expansion support for vector multiplication
by uniform constants using shifts and additions like we have for scalar
multiplication, but that is something that can be done in stage1.

2021-03-13  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/99544
	* match.pd (X + (X << C) -> X * (1 + (1 << C))): Don't simplify
	if for vector types multiplication can't be done in type's mode.

	* gcc.dg/gomp/pr99544.c: New test.