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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/111591] ppc64be: miscompilation with -mstrict-align /
 -O3
Date: Thu, 19 Oct 2023 11:06:08 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111591

--- Comment #22 from Richard Biener <rguenth at gcc dot gnu.org> ---
I see the mems properly get their base adjusted:

(insn 384 383 0 (set (mem/c:V2DI (plus:DI (reg/f:DI 112 virtual-stack-vars)
                (const_int 16 [0x10])) [7 MEM[(struct Vec128D.30433 *)_10]+0
S16 A128])
        (reg:V2DI 616)) -1
     (nil))

vs.

(insn 389 388 390 (set (reg:HI 619)
        (mem/c:HI (plus:DI (reg/f:DI 112 virtual-stack-vars)
                (const_int 16 [0x10])) [4 MEM[(struct Vec128D.30212
*)_10].rawD.30221[0]+0 S2 A128])) "test.cc":218:14 -1
     (nil))

both are based off a fake _10.  But we get alias sets 7 and 4 used here
which might be a problem.

See update_alias_info_with_stack_vars and uses of decls_to_pointers,
in particular from set_mem_attributes_minus_bitpos where we preserve
TBAA info with the rewrite.  I'm not sure why that should be OK ...
(but I'm sure I must have thought of this problem back in time)

Does the following fix the testcase?

diff --git a/gcc/emit-rtl.cc b/gcc/emit-rtl.cc
index 84b6833225e..81c0a63eddc 100644
--- a/gcc/emit-rtl.cc
+++ b/gcc/emit-rtl.cc
@@ -2128,7 +2128,7 @@ set_mem_attributes_minus_bitpos (rtx ref, tree t, int
objectp,
              tree *orig_base =3D &attrs.expr;
              while (handled_component_p (*orig_base))
                orig_base =3D &TREE_OPERAND (*orig_base, 0);
-             tree aptrt =3D reference_alias_ptr_type (*orig_base);
+             tree aptrt =3D ptr_type_node;
              *orig_base =3D build2 (MEM_REF, TREE_TYPE (*orig_base), *name=
p,
                                   build_int_cst (aptrt, 0));
            }=