[Backport RFA] lra: Avoid unfolded plus-0

[Richard Sandiford <richard.sandiford@arm.com>]

Vlad, is it OK if I backport the patch below to fix
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111528 ?  Jakub has
given a conditional OK on irc.

Thanks,
Richard

Richard Sandiford <richard.sandiford@arm.com> writes:
> While backporting another patch to an earlier release, I hit a
> situation in which lra_eliminate_regs_1 would eliminate an address to:
>
>     (plus (reg:P R) (const_int 0))
>
> This address compared not-equal to plain:
>
>     (reg:P R)
>
> which caused an ICE in a later peephole2.  (The ICE showed up in
> gfortran.fortran-torture/compile/pr80464.f90 on the branch but seems
> to be latent on trunk.)
>
> These unfolded PLUSes shouldn't occur in the insn stream, and later code
> in the same function tried to avoid them.
>
> Tested on aarch64-linux-gnu so far, but I'll test on x86_64-linux-gnu too.
> Does this look OK?
>
> There are probably other instances of the same thing elsewhere,
> but it seemed safer to stick to the one that caused the issue.
>
> Thanks,
> Richard
>
>
> gcc/
> 	* lra-eliminations.cc (lra_eliminate_regs_1): Use simplify_gen_binary
> 	rather than gen_rtx_PLUS.
> ---
>  gcc/lra-eliminations.cc | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/gcc/lra-eliminations.cc b/gcc/lra-eliminations.cc
> index df613cdda76..4daaff1a124 100644
> --- a/gcc/lra-eliminations.cc
> +++ b/gcc/lra-eliminations.cc
> @@ -406,7 +406,7 @@ lra_eliminate_regs_1 (rtx_insn *insn, rtx x, machine_mode mem_mode,
>  		elimination_fp2sp_occured_p = true;
>  
>  	      if (! update_p && ! full_p)
> -		return gen_rtx_PLUS (Pmode, to, XEXP (x, 1));
> +		return simplify_gen_binary (PLUS, Pmode, to, XEXP (x, 1));
>  
>  	      if (maybe_ne (update_sp_offset, 0))
>  		offset = ep->to_rtx == stack_pointer_rtx ? update_sp_offset : 0;