On 12/13/24 8:20 AM, Jakub Jelinek wrote:
Hi!
The following testcase is miscompiled on s390x-linux with -O2 -march=z15.
The problem happens during cse2, which sees in an extended basic block
(jump_insn 217 78 216 10 (parallel [
(set (pc)
(if_then_else (ne (reg:SI 165)
(const_int 1 [0x1]))
(label_ref 216)
(pc)))
(set (reg:SI 165)
(plus:SI (reg:SI 165)
(const_int -1 [0xffffffffffffffff])))
(clobber (scratch:SI))
(clobber (reg:CC 33 %cc))
]) "t.c":14:17 discrim 1 2192 {doloop_si64}
(int_list:REG_BR_PROB 955630228 (nil))
-> 216)
...
(insn 99 98 100 12 (set (reg:SI 138)
(const_int 1 [0x1])) "t.c":9:31 1507 {*movsi_zarch}
(nil))
(insn 100 99 103 12 (parallel [
(set (reg:SI 137)
(minus:SI (reg:SI 138)
(subreg:SI (reg:HI 135 [ a ]) 0)))
(clobber (reg:CC 33 %cc))
]) "t.c":9:31 1904 {*subsi3}
(expr_list:REG_DEAD (reg:SI 138)
(expr_list:REG_DEAD (reg:HI 135 [ a ])
(expr_list:REG_UNUSED (reg:CC 33 %cc)
(nil)))))
I don't really see the connection between (reg 165) and (reg 138), but I
don't think it matters enough to dive into.
This optimization isn't correct here though, because the JUMP_INSN has
multiple sets. Before r0-77890 record_jump_equiv has been called from
cse_insn guarded on n_sets == 1 && any_condjump_p (insn), so it wouldn't
be done on the above JUMP_INSN where n_sets == 2. But since that change
it is guarded with single_set (insn) && any_condjump_p (insn) and that
is true because of the REG_UNUSED note. Looking at that note is
inappropriate in CSE though, because the whole intent of the pass is to
extend the lifetimes of the pseudos if equivalence is found, so the fact
that there is REG_UNUSED note for (reg:SI 165) and that the reg isn't used
later doesn't imply that it won't be used after the optimization.
Exactly. CSE inherently trashes the meaning of REG_UNUSED notes
The patch below adds !multiple_sets (insn) check instead of replacing with
it the single_set (insn) check, because apparently any_condjump_p uses
pc_set which supports the case where PATTERN is a SET to PC (that is a
single_set (insn) && !multiple_sets (insn), PATTERN is a PARALLEL with a
single SET to PC (likewise) and some CLOBBERs, PARALLEL with two or more
SETs where the first one is SET to PC (that could be single_set (insn)
with REG_UNUSED notes but is not !multiple_sets (insn)) or PATTERN
is UNSPEC/UNSPEC_VOLATILE with SET inside of it. For the last case
!multiple_sets (insn) will be true, but IMHO we shouldn't try to derive
anything from those because we haven't checked the rest of the UNSPEC*
and we don't really know what it does.
Right.
Bootstrapped/regtested on {x86_64,i686,aarch64,powerpc64le,s390x}-linux, ok
for trunk?
2024-12-13 Jakub Jelinek <ja...@redhat.com>
PR rtl-optimization/117095
* cse.cc (cse_extended_basic_block): Don't call record_jump_equiv
if multiple_sets (insn).
* gcc.c-torture/execute/pr117095.c: New test.
OK
jeff
