reassoc: Reassociate integral multiplies [PR95867]

reassoc: Reassociate integral multiplies [PR95867]

For floating point multiply, we have nice code in reassoc to reassociate
multiplications to almost optimal sequence of as few multiplications as
possible (or library call), but for integral types we just give up
because there is no __builtin_powi* for those types.

As there is no library routine we could use, instead of adding new internal
call just to hold it temporarily and then lower to multiplications again,
this patch for the integral types calls into the sincos pass routine that
expands it into multiplications right away.

2021-01-11  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/95867
	* tree-ssa-math-opts.h: New header.
	* tree-ssa-math-opts.c: Include tree-ssa-math-opts.h.
	(powi_as_mults): No longer static.  Use build_one_cst instead of
	build_real.  Formatting fix.
	* tree-ssa-reassoc.c: Include tree-ssa-math-opts.h.
	(attempt_builtin_powi): Handle multiplication reassociation without
	powi_fndecl using powi_as_mults.
	(reassociate_bb): For integral types don't require
	-funsafe-math-optimizations to call attempt_builtin_powi.

	* gcc.dg/tree-ssa/pr95867.c: New test.