Re: [PATCH] bswap: Fix up recent vector CONSTRUCTOR optimization [PR98568]

[Richard Biener <rguenther@suse.de>]

On Thu, 7 Jan 2021, Jakub Jelinek wrote:

> Hi!
> 
> As the testcase shows, bswap can match even byte-swapping or indentity
> from low part of some wider SSA_NAME.
> For bswap replacement other than for vector CONSTRUCTOR the code has been
> using NOP_EXPR casts if the types weren't compatible, but for vectors
> we need to use VIEW_CONVERT_EXPR.  The problem with the latter is that
> we require that it has the same size, which isn't guaranteed, so this patch
> in those cases first adds a narrowing NOP_EXPR cast and only afterwards
> does a VIEW_CONVERT_EXPR.
> 
> Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok for
> trunk?

OK.

Thanks,
Richard.

> 2021-01-06  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR tree-optimization/98568
> 	* gimple-ssa-store-merging.c (bswap_view_convert): New function.
> 	(bswap_replace): Use it.
> 
> 	* g++.dg/torture/pr98568.C: New test.
> 
> --- gcc/gimple-ssa-store-merging.c.jj	2021-01-05 16:15:58.965337667 +0100
> +++ gcc/gimple-ssa-store-merging.c	2021-01-06 19:20:37.225578412 +0100
> @@ -978,6 +978,25 @@ public:
>  
>  }; // class pass_optimize_bswap
>  
> +/* Helper function for bswap_replace.  Build VIEW_CONVERT_EXPR from
> +   VAL to TYPE.  If VAL has different type size, emit a NOP_EXPR cast
> +   first.  */
> +
> +static tree
> +bswap_view_convert (gimple_stmt_iterator *gsi, tree type, tree val)
> +{
> +  gcc_assert (INTEGRAL_TYPE_P (TREE_TYPE (val)));
> +  if (TYPE_SIZE (type) != TYPE_SIZE (TREE_TYPE (val)))
> +    {
> +      HOST_WIDE_INT prec = TREE_INT_CST_LOW (TYPE_SIZE (type));
> +      tree itype = build_nonstandard_integer_type (prec, 1);
> +      gimple *g = gimple_build_assign (make_ssa_name (itype), NOP_EXPR, val);
> +      gsi_insert_before (gsi, g, GSI_SAME_STMT);
> +      val = gimple_assign_lhs (g);
> +    }
> +  return build1 (VIEW_CONVERT_EXPR, type, val);
> +}
> +
>  /* Perform the bswap optimization: replace the expression computed in the rhs
>     of gsi_stmt (GSI) (or if NULL add instead of replace) by an equivalent
>     bswap, load or load + bswap expression.
> @@ -1100,7 +1119,7 @@ bswap_replace (gimple_stmt_iterator gsi,
>  	      gimple_set_vuse (load_stmt, n->vuse);
>  	      gsi_insert_before (&gsi, load_stmt, GSI_SAME_STMT);
>  	      if (conv_code == VIEW_CONVERT_EXPR)
> -		val_tmp = build1 (VIEW_CONVERT_EXPR, TREE_TYPE (tgt), val_tmp);
> +		val_tmp = bswap_view_convert (&gsi, TREE_TYPE (tgt), val_tmp);
>  	      gimple_assign_set_rhs_with_ops (&gsi, conv_code, val_tmp);
>  	      update_stmt (cur_stmt);
>  	    }
> @@ -1144,7 +1163,7 @@ bswap_replace (gimple_stmt_iterator gsi,
>  	  if (!is_gimple_val (src))
>  	    return NULL_TREE;
>  	  if (conv_code == VIEW_CONVERT_EXPR)
> -	    src = build1 (VIEW_CONVERT_EXPR, TREE_TYPE (tgt), src);
> +	    src = bswap_view_convert (&gsi, TREE_TYPE (tgt), src);
>  	  g = gimple_build_assign (tgt, conv_code, src);
>  	}
>        else if (cur_stmt)
> @@ -1227,7 +1246,7 @@ bswap_replace (gimple_stmt_iterator gsi,
>        tmp = make_temp_ssa_name (bswap_type, NULL, "bswapdst");
>        tree atmp = tmp;
>        if (conv_code == VIEW_CONVERT_EXPR)
> -	atmp = build1 (VIEW_CONVERT_EXPR, TREE_TYPE (tgt), tmp);
> +	atmp = bswap_view_convert (&gsi, TREE_TYPE (tgt), tmp);
>        convert_stmt = gimple_build_assign (tgt, conv_code, atmp);
>        gsi_insert_after (&gsi, convert_stmt, GSI_SAME_STMT);
>      }
> --- gcc/testsuite/g++.dg/torture/pr98568.C.jj	2021-01-06 19:19:25.940377456 +0100
> +++ gcc/testsuite/g++.dg/torture/pr98568.C	2021-01-06 19:19:16.608482074 +0100
> @@ -0,0 +1,37 @@
> +// PR tree-optimization/98568
> +// { dg-do compile }
> +
> +char a[2];
> +char b[4];
> +
> +void
> +foo (int x)
> +{
> +  a[1] = x >> 8;
> +  a[0] = x;
> +}
> +
> +void
> +bar (long long x)
> +{
> +  b[3] = x >> 24;
> +  b[2] = x >> 16;
> +  b[1] = x >> 8;
> +  b[0] = x;
> +}
> +
> +void
> +baz (int x)
> +{
> +  a[0] = x >> 8;
> +  a[1] = x;
> +}
> +
> +void
> +qux (long long x)
> +{
> +  b[0] = x >> 24;
> +  b[1] = x >> 16;
> +  b[2] = x >> 8;
> +  b[3] = x;
> +}
> 
> 	Jakub
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)