[Bug rtl-optimization/123786] [16 Regression] AArch64: Miscompile at -O3 -mtune=generic-armv9-a

[artemiyv at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123786

--- Comment #8 from Artemiy Volkov <artemiyv at gcc dot gnu.org> ---
Moving the second insn across basic blocks looks really wrong.  The quickest
workaround is to just explicitly forbid that:

diff --git a/gcc/dep-fusion.cc b/gcc/dep-fusion.cc
index c849da101f9..e2f8363a2b7 100644
--- a/gcc/dep-fusion.cc
+++ b/gcc/dep-fusion.cc
@@ -99,6 +99,7 @@ pass_dep_fusion::execute (function *fn)

       rtl_ssa::use_info *use_insn = def->single_nondebug_insn_use ();
       if (!use_insn
+         || use_insn->bb() != insn->bb()
          || !use_insn->insn ()->can_be_optimized ()
          || !targetm.sched.macro_fusion_pair_p (insn->rtl (),
                                                 use_insn->insn ()->rtl ()))

Cross-BB movements aren't very interesting in the context of this pass anyway,
I think.