[gcc r12-10555] cfgrtl: Fix MEM_EXPR update in duplicate_insn_chain [PR114924]

[Richard Biener]

https://gcc.gnu.org/g:33663c0701a723846527f9bf2ea01d67d7033c0b

commit r12-10555-g33663c0701a723846527f9bf2ea01d67d7033c0b
Author: Alex Coplan <alex.coplan@arm.com>
Date:   Fri May 3 09:23:59 2024 +0100

    cfgrtl: Fix MEM_EXPR update in duplicate_insn_chain [PR114924]
    
    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.
    
    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.
    
    (cherry picked from commit fe40d525619eee9c2821126390df75068df4773a)

Diff:
---
 gcc/cfgrtl.cc | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/gcc/cfgrtl.cc b/gcc/cfgrtl.cc
index 8decf4007e83..a8c95d82a2a7 100644
--- a/gcc/cfgrtl.cc
+++ b/gcc/cfgrtl.cc
@@ -4374,12 +4374,13 @@ 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);
 		      }
 		  }
 	    }