https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82991
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Found it (old tree):
Index: tree-ssa-sccvn.c
===================================================================
--- tree-ssa-sccvn.c (revision 254072)
+++ tree-ssa-sccvn.c (working copy)
@@ -4123,6 +4234,25 @@ visit_use (tree use)
changed = defs_to_varying (call_stmt);
goto done;
}
+
+ int rflags = gimple_call_return_flags (call_stmt);
+ if (rflags & ERF_RETURNS_ARG)
+ {
+ unsigned argnum = rflags & ERF_RETURN_ARG_MASK;
+ if (argnum < gimple_call_num_args (call_stmt))
+ {
+ tree arg = gimple_call_arg (call_stmt, argnum);
+ if (TREE_CODE (arg) == SSA_NAME
+ /*|| is_gimple_min_invariant (arg)*/)
+ {
+ changed = visit_copy (lhs, arg);
+ if (gimple_vdef (call_stmt))
+ changed |= set_ssa_val_to (gimple_vdef (call_stmt),
+ gimple_vdef (call_stmt));
+ goto done;
+ }
+ }
+ }
}
/* Pick up flags from a devirtualization target. */
Index: tree-ssa-pre.c
===================================================================
--- tree-ssa-pre.c (revision 254072)
+++ tree-ssa-pre.c (working copy)
@@ -4309,6 +4369,14 @@ eliminate_dom_walker::before_dom_childre
eliminate_push_avail (sprime);
}
+ /* While we might have value numbered a call return value to
+ one of its arguments the call itself might not be solely
+ represented by its return value. Thus do not ignore
+ side-effects indicated by a VARYING vdef. */
+ if (gimple_vdef (stmt)
+ && VN_INFO (gimple_vdef (stmt))->valnum == gimple_vdef (stmt))
+ sprime = NULL_TREE;
+
/* If this now constitutes a copy duplicate points-to
and range info appropriately. This is especially
important for inserted code. See tree-ssa-copy.c
