cfgrtl: Fix MEM_EXPR update in duplicate_insn_chain [PR114924]

[Alex Coplan]

Hi,

The PR shows that when cfgrtl.cc:duplicate_insn_chain attempts to
update the MR_DEPENDENCE_CLIQUE information for a MEM_EXPR we can end up
accidentally dropping (e.g.) an ARRAY_REF from the MEM_EXPR and end up
replacing it with the underlying MEM_REF.  This leads to an
inconsistency in the MEM_EXPR information, and could lead to wrong code.

While the walk down to the MEM_REF is necessary to update
MR_DEPENDENCE_CLIQUE, we should use the outer tree expression for the
MEM_EXPR.  This patch does that.

Bootstrapped/regtested on aarch64-linux-gnu, no regressions.  OK for
trunk?  What about backports?

Thanks,
Alex

gcc/ChangeLog:

        PR rtl-optimization/114924
        * cfgrtl.cc (duplicate_insn_chain): When updating MEM_EXPRs,
        don't strip (e.g.) ARRAY_REFs from the final MEM_EXPR.

diff --git a/gcc/cfgrtl.cc b/gcc/cfgrtl.cc
index 304c429c99b..a5dc3512159 100644
--- a/gcc/cfgrtl.cc
+++ b/gcc/cfgrtl.cc
@@ -4432,12 +4432,13 @@ duplicate_insn_chain (rtx_insn *from, rtx_insn *to,
                           since MEM_EXPR is shared so make a copy and
                           walk to the subtree again.  */
                        tree new_expr = unshare_expr (MEM_EXPR (*iter));
+                       tree orig_new_expr = new_expr;
                        if (TREE_CODE (new_expr) == WITH_SIZE_EXPR)
                          new_expr = TREE_OPERAND (new_expr, 0);
                        while (handled_component_p (new_expr))
                          new_expr = TREE_OPERAND (new_expr, 0);
                        MR_DEPENDENCE_CLIQUE (new_expr) = newc;
-                       set_mem_expr (const_cast <rtx> (*iter), new_expr);
+                       set_mem_expr (const_cast <rtx> (*iter), orig_new_expr);
                      }
                  }
            }