Re: [PATCH][2/2] gimple-fold.c part for PR83141

[Richard Biener <rguenther@suse.de>]

On Mon, 27 Nov 2017, Richard Biener wrote:

> 
> The following is the truly minimal fix for the middle-end issue
> with SRA and memcpy folding interaction.  I've tried more variants
> that "make sense" but as they all end up folding slightly more
> memcpy calls than before we run into optimization testcase
> regressions in places that look for __builtin_memcpy and do
> not deal with aggregate copies as MEM[..] = MEM[..];
> 
> Bootstrap and regtest running on x86_64-unknown-linux-gnu.
> 
> GCC 9 is the time we can try dealing with such fallout, it just
> doesn't feel like the correct time to do now...

Installed as follows, bootstrapped and tested on x86_64-unknown-linux-gnu.

Richard.

2017-11-28  Richard Biener  <rguenther@suse.de>

	PR middle-end/83141
	* gimple-fold.c (gimple_fold_builtin_memory_op): For aggregate
	copies generated from memcpy use a character array as reference
	type.

Index: gcc/gimple-fold.c
===================================================================
--- gcc/gimple-fold.c	(revision 255196)
+++ gcc/gimple-fold.c	(working copy)
@@ -1039,8 +1039,24 @@ gimple_fold_builtin_memory_op (gimple_st
 	      gimple_set_vuse (new_stmt, gimple_vuse (stmt));
 	      gsi_insert_before (gsi, new_stmt, GSI_SAME_STMT);
 	    }
+	  new_stmt = gimple_build_assign (destvar, srcvar);
+	  goto set_vop_and_replace;
 	}
-      new_stmt = gimple_build_assign (destvar, srcvar);
+
+      /* We get an aggregate copy.  Use an unsigned char[] type to
+	 perform the copying to preserve padding and to avoid any issues
+	 with TREE_ADDRESSABLE types or float modes behavior on copying.  */
+      desttype = build_array_type_nelts (unsigned_char_type_node,
+					 tree_to_uhwi (len));
+      srctype = desttype;
+      if (src_align > TYPE_ALIGN (srctype))
+	srctype = build_aligned_type (srctype, src_align);
+      if (dest_align > TYPE_ALIGN (desttype))
+	desttype = build_aligned_type (desttype, dest_align);
+      new_stmt
+	= gimple_build_assign (fold_build2 (MEM_REF, desttype, dest, off0),
+			       fold_build2 (MEM_REF, srctype, src, off0));
+set_vop_and_replace:
       gimple_set_vuse (new_stmt, gimple_vuse (stmt));
       gimple_set_vdef (new_stmt, gimple_vdef (stmt));
       if (gimple_vdef (new_stmt)