Hi!
The following patch is a partial fix for PR80491, an improvement for
if-conversion if there is empty else_bb.
What we do right now is in that case we only look at the immediately
preceeding (non-debug/non-note) instruction before cond_earliest
and if it is not the set of x, we just turn it into attempt to
use previous value of x rather than whatever it has been initialized to.
On the testcases from the PR, we have:
(insn 7 4 8 2 (set (reg:DI 97 [ _15+8 ])
(const_int 0 [0])) 81 {*movdi_internal}
(nil))
(insn 8 7 9 2 (set (reg:DI 104 [ a_11(D)->low ])
(mem:DI (reg/v/f:DI 101 [ a ]) [2 a_11(D)->low+0 S8 A64])) 81 {*movdi_internal}
(nil))
(insn 9 8 10 2 (set (reg:DI 105 [ b_12(D)->low ])
(mem:DI (reg/v/f:DI 102 [ b ]) [2 b_12(D)->low+0 S8 A64])) 81 {*movdi_internal}
(nil))
(insn 10 9 11 2 (parallel [
(set (reg:CCC 17 flags)
(compare:CCC (plus:DI (reg:DI 104 [ a_11(D)->low ])
(reg:DI 105 [ b_12(D)->low ]))
(reg:DI 104 [ a_11(D)->low ])))
(set (reg:DI 103)
(plus:DI (reg:DI 104 [ a_11(D)->low ])
(reg:DI 105 [ b_12(D)->low ])))
]) 316 {*adddi3_cc_overflow_1}
(expr_list:REG_DEAD (reg:DI 105 [ b_12(D)->low ])
(expr_list:REG_DEAD (reg:DI 104 [ a_11(D)->low ])
(nil))))
(jump_insn 11 10 14 2 (set (pc)
(if_then_else (ltu (reg:CCC 17 flags)
(const_int 0 [0]))
(label_ref 14)
(pc))) 617 {*jcc_1}
(expr_list:REG_DEAD (reg:CCC 17 flags)
(int_list:REG_BR_PROB 4 (nil)))
-> 14)
(code_label 14 11 35 3 3 (nil) [1 uses])
(note 35 14 15 3 [bb 3] NOTE_INSN_BASIC_BLOCK)
(insn 15 35 16 3 (set (reg:DI 97 [ _15+8 ])
(const_int 1 [0x1])) 81 {*movdi_internal}
(nil))
(code_label 16 15 36 4 2 (nil) [0 uses])
If insn 7 would come after insn 9 (which doesn't change the behavior, as
insn 8 and insn 9 don't clobber pseudo 97 and const_int 0 is constant),
we'd turn that into a setcc pattern, but otherwise we fail.
This patch let us search for x's setter earlier in the bb.
During testing I found that modified_in_p/modified_in_between_p don't
actually take into account calls that could change MEMs, so the patch
handles that too.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
During bootstrap/regtest it seems to trigger over 10000 times, but
my statistics collection only noted cases where it found an earlier setter
and the noce_process_if_block has been successful, has not attempted to
check if insn_b/set_b was NULL whether it would otherwise fail (but even
in cases where it doesn't fail perhaps with the patch it can generate
better code).
2017-04-25 Jakub Jelinek <jakub@redhat.com>
PR rtl-optimization/80491
* ifcvt.c (noce_process_if_block): When looking for x setter
with missing else_bb, don't check only the insn right before
cond_earliest, but look for the last insn that x is modified in
within the same bb.