[gcc r14-8369] aarch64: Re-parent trailing nondebug base reg uses [PR113089]

[Alex Coplan]

https://gcc.gnu.org/g:49bfda6017e105df46fa8d12d7f067da423a1d3c

commit r14-8369-g49bfda6017e105df46fa8d12d7f067da423a1d3c
Author: Alex Coplan <alex.coplan@arm.com>
Date:   Mon Jan 15 17:13:06 2024 +0000

    aarch64: Re-parent trailing nondebug base reg uses [PR113089]
    
    While working on PR113089, I realised we where missing code to re-parent
    trailing nondebug uses of the base register in the case of cancelling
    writeback in the load/store pair pass.  This patch fixes that.
    
    gcc/ChangeLog:
    
            PR target/113089
            * config/aarch64/aarch64-ldp-fusion.cc (ldp_bb_info::fuse_pair):
            Update trailing nondebug uses of the base register in the case
            of cancelling writeback.

Diff:
---
 gcc/config/aarch64/aarch64-ldp-fusion.cc | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/gcc/config/aarch64/aarch64-ldp-fusion.cc b/gcc/config/aarch64/aarch64-ldp-fusion.cc
index bbb95d6c820..e3827e98010 100644
--- a/gcc/config/aarch64/aarch64-ldp-fusion.cc
+++ b/gcc/config/aarch64/aarch64-ldp-fusion.cc
@@ -1693,6 +1693,30 @@ ldp_bb_info::fuse_pair (bool load_p,
 
   if (trailing_add)
     changes.safe_push (make_delete (trailing_add));
+  else if ((writeback & 2) && !writeback_effect)
+    {
+      // The second insn initially had writeback but now the pair does not,
+      // need to update any nondebug uses of the base register def in the
+      // second insn.  We'll take care of debug uses later.
+      auto def = find_access (insns[1]->defs (), base_regno);
+      gcc_assert (def);
+      auto set = dyn_cast<set_info *> (def);
+      if (set && set->has_nondebug_uses ())
+	{
+	  auto orig_use = find_access (insns[0]->uses (), base_regno);
+	  for (auto use : set->nondebug_insn_uses ())
+	    {
+	      auto change = make_change (use->insn ());
+	      change->new_uses = check_remove_regno_access (attempt,
+							    change->new_uses,
+							    base_regno);
+	      change->new_uses = insert_access (attempt,
+						orig_use,
+						change->new_uses);
+	      changes.safe_push (change);
+	    }
+	}
+    }
 
   auto is_changing = insn_is_changing (changes);
   for (unsigned i = 0; i < changes.length (); i++)