i386: Fix up df uses in i386 splitters [PR99104]

i386: Fix up df uses in i386 splitters [PR99104]

The following testcase started ICEing with my recent changes to enable
split4 after sel-sched, but it seems the bug is more general.
Some of the i386 splitter condition functions use and rely on df, but
the split passes don't really df_analyze/df_finish_pass, so the DF info
may be stale or not computed at all - the particular ICE is because
there is a new bb and df_get_live_out (bb) returns NULL on it as the
live or lr problem has not been computed yet.

This patch fixes it by not calling ix86_ok_to_clobber_flags from
ix86_avoid_lea_for_add where it wasn't ever needed because the splitters
using that function as condition have (clobber FLAGS) in their pattern.
And, changes the ix86_avoid_lea_for_addr using splitter from normal splitter
to peephole2 splitter that uses peep2_regno_dead_p infrastructure to
determine if FLAGS is dead.  Also, it saves and restores recog_data
variable around the call to distance_non_agu_define and doesn't call
extract_insn_data there, because split_insns or peephole2_insns just
clear recog_data.insn and then fill in recog_data.operand array, and so
might not match what extract_insn will do on the insn at all.

2021-02-18  Jakub Jelinek  <jakub@redhat.com>

	PR target/99104
	* config/i386/i386.c (distance_non_agu_define): Don't call
	extract_insn_cached here.
	(ix86_lea_outperforms): Save and restore recog_data around call
	to distance_non_agu_define and distance_agu_use.
	(ix86_ok_to_clobber_flags): Remove.
	(ix86_avoid_lea_for_add): Don't call ix86_ok_to_clobber_flags.
	(ix86_avoid_lea_for_addr): Likewise.  Adjust function comment.
	* config/i386/i386.md (*lea<mode>): Change from define_insn_and_split
	into define_insn.  Move the splitting to define_peephole2 and
	check there using peep2_regno_dead_p if FLAGS_REG is dead.

	* gcc.dg/pr99104.c: New test.