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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/110924] [14 Regression] ICE on valid code at
 -O{s,2,3} on x86_64-linux-gnu: verify_ssa failed
Date: Tue, 08 Aug 2023 10:26:33 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110924

--- Comment #12 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #11)
> Variant (1) is just the following, but I'm unsure as to the possible effe=
cts
> of that ... (test coverage will be very low anyway)
>=20
> diff --git a/gcc/tree-ssa-operands.cc b//gcc/tree-ssa-operands.cc
> index 57e393ae164..c8ac98b4e06 100644
> --- a/gcc/tree-ssa-operands.cc
> +++ b/gcc/tree-ssa-operands.cc
> @@ -696,7 +696,8 @@ operands_scanner::maybe_add_call_vops (gcall *stmt)
>        /* A 'pure' or a 'const' function never call-clobbers anything.  */
>        if (!(call_flags & (ECF_PURE | ECF_CONST)))
>         add_virtual_operand (opf_def);
> -      else if (!(call_flags & ECF_CONST))
> +      else if (!(call_flags & ECF_CONST)
> +              || (call_flags & ECF_NORETURN))
>         add_virtual_operand (opf_use);
>      }
>  }

That ICEs for example tree-ssa/cunroll-4.c because that inserts
__builtin_unreachable () calls and this function is explicitly
marked const noreturn (if you use that combo manually you get a diagnostic).
The ICE is because cunroll doesn't add virtual operands or updates SSA.

But it also shows that sinking into __builtin_unreachable () ending regions
will have the same issue and the ipa pure-const/modref fix won't fix that.

I'm going to try fixing the live problem :/=