Re: [PATCH][v2] tree-optimization/107389 - honor __builtin_assume_alignment at -O0

[Jakub Jelinek <jakub@redhat.com>]

On Tue, Nov 08, 2022 at 01:53:48PM +0100, Richard Biener wrote:
> The following makes sure to set alignment information on the LHS
> of __builtin_assume_alignment calls even when not optimizing so
> uses as arguments to builtin functions like memcpy or __atomic_load_n
> can be reflected at RTL expansion time.
> 
> Bootstrap and regtest running on x86_64-unknown-linux-gnu, OK?
> 
> Thanks,
> Richard.
> 
> 	PR tree-optimization/107389
> 	* gimple-low.cc (lower_builtin_assume_aligned): New.
> 	(lower_stmt): Call it.
> 
> 	* gcc.dg/pr107389.c: New testcase.
> ---
>  gcc/gimple-low.cc               | 41 +++++++++++++++++++++++++++++++++
>  gcc/testsuite/gcc.dg/pr107389.c | 13 +++++++++++
>  2 files changed, 54 insertions(+)
>  create mode 100644 gcc/testsuite/gcc.dg/pr107389.c
> 
> diff --git a/gcc/gimple-low.cc b/gcc/gimple-low.cc
> index 512aa9feada..f9bcb772163 100644
> --- a/gcc/gimple-low.cc
> +++ b/gcc/gimple-low.cc
> @@ -84,6 +84,7 @@ static void lower_try_catch (gimple_stmt_iterator *, struct lower_data *);
>  static void lower_gimple_return (gimple_stmt_iterator *, struct lower_data *);
>  static void lower_builtin_setjmp (gimple_stmt_iterator *);
>  static void lower_builtin_posix_memalign (gimple_stmt_iterator *);
> +static void lower_builtin_assume_aligned (gimple_stmt_iterator *);
>  
>  
>  /* Lower the body of current_function_decl from High GIMPLE into Low
> @@ -768,6 +769,13 @@ lower_stmt (gimple_stmt_iterator *gsi, struct lower_data *data)
>  		lower_builtin_posix_memalign (gsi);
>  		return;
>  	      }
> +	    else if (DECL_FUNCTION_CODE (decl) == BUILT_IN_ASSUME_ALIGNED
> +		     && !optimize)
> +	      {
> +		lower_builtin_assume_aligned (gsi);
> +		data->cannot_fallthru = false;
> +		return;
> +	      }
>  	  }
>  
>  	if (decl && (flags_from_decl_or_type (decl) & ECF_NORETURN))
> @@ -1310,6 +1318,39 @@ lower_builtin_posix_memalign (gimple_stmt_iterator *gsi)
>    gsi_insert_after (gsi, stmt, GSI_NEW_STMT);
>    gsi_insert_after (gsi, gimple_build_label (noalign_label), GSI_NEW_STMT);
>  }
> +
> +/* Lower calls to __builtin_assume_aligned when not optimizing.  */
> +
> +static void
> +lower_builtin_assume_aligned (gimple_stmt_iterator *gsi)
> +{
> +  gcall *call = as_a <gcall *> (gsi_stmt (*gsi));
> +
> +  tree lhs = gimple_call_lhs (call);
> +  if (!lhs || !POINTER_TYPE_P (TREE_TYPE (lhs)))
> +    return;

I think nothing checks that TREE_CODE (lhs) == SSA_NAME,
that isn't guaranteed before ssa pass.
Otherwise LGTM.

	Jakub