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From: "rsandifo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/111411] [14 regression] ICE when building opus-1.4,
 unrecognizable insn with -fstack-protector-strong
Date: Thu, 14 Sep 2023 18:41:04 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111411

--- Comment #7 from Richard Sandiford <rsandifo at gcc dot gnu.org> ---
It's proving difficult to generate a reliable reproducer from
pure C code, due to the ways in which we handle out-of-range
offsets.  But FWIW, here's one that uses the RTL frontend,
compiled with -O -fdisable-rtl-postreload -fpeephole2:

extern int data[];

void __RTL (startwith ("ira")) foo (void *ptr)
{
  (function "foo"
    (param "ptr"
      (DECL_RTL (reg/v:DI <0> [ ptr ]))
      (DECL_RTL_INCOMING (reg/v:DI x0 [ ptr ]))
    ) ;; param "ptr"
    (insn-chain
      (block 2
        (edge-from entry (flags "FALLTHRU"))
        (cnote 3 [bb 2] NOTE_INSN_BASIC_BLOCK)
        (insn 4 (set (reg:DI <0>) (reg:DI x0)))
        (insn 5 (set (reg:DI <1>)
                     (plus:DI (reg:DI <0>) (const_int 768))))
        (insn 6 (set (mem:SI (plus:DI (reg:DI <0>)
                                      (const_int 508)) [1 &data+508 S4 A4])
                     (const_int 0)))
        (insn 7 (set (mem:SI (plus:DI (reg:DI <1>)
                                      (const_int -256)) [1 &data+512 S4 A4])
                     (const_int 0)))
        (edge-to exit (flags "FALLTHRU"))
      ) ;; block 2
    ) ;; insn-chain
  ) ;; function
}

(This one doesn't rely on -fstack-protector-strong, or on the recent
patches.)

The problem is that the LDP/STP formation code is too loose in the
check for valid addresses: it thinks it's enough for the second address
to be valid, even though that's not the one used in the STP.=