tree-ssa-math-opts.c (convert_plusminus_to_widen): Call has_single_use () and not do the conversion if...

gcc/

	* tree-ssa-math-opts.c (convert_plusminus_to_widen): Call
	has_single_use () and not do the conversion if has_single_use ()
	returns false for the multiplication result.

gcc/testsuite/

	* gcc.dg/wmul-1.c: New test.

From-SVN: r204072