g:3bd29185 mishandled the case in which only the
tail end of a multireg hard register is invalidated by the call.
Walking all the entries should be both safer and more precise.

Avoiding cselib_invalidate_regno also means that we no longer
walk the same list multiple times (which is something we did
before g:3bd29185 too).

2020-01-27  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	PR rtl-optimization/93170
	* cselib.c (cselib_invalidate_regno_val): New function, split out
	from...
	(cselib_invalidate_regno): ...here.
	(cselib_invalidated_by_call_p): New function.
	(cselib_process_insn): Iterate over all the hard-register entries in
	REG_VALUES and invalidate any that cross call-clobbered registers.

gcc/testsuite/
	* gcc.dg/torture/pr93170.c: New test.