tree-optimization/94163 constrain alignment set by PRE

This avoids HWI -> unsigned truncation to end up with zero alignment
which set_ptr_info_alignment ICEs on.

2020-03-13  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/94163
	* tree-ssa-pre.c (create_expression_by_pieces): Check
	whether alignment would be zero.

gcc/ChangeLog

+2020-03-13  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/94163
+	* tree-ssa-pre.c (create_expression_by_pieces): Check
+	whether alignment would be zero.
+
 2020-03-13  Martin Liska  <mliska@suse.cz>
 
 	PR lto/94157

gcc/tree-ssa-pre.c

@@ -2815,7 +2815,8 @@ create_expression_by_pieces (basic_block block, pre_expr expr,
 	      unsigned HOST_WIDE_INT hmisalign
 		= args.length () == 3 ? tree_to_uhwi (args[2]) : 0;
 	      if ((halign & (halign - 1)) == 0
-		  && (hmisalign & ~(halign - 1)) == 0)
+		  && (hmisalign & ~(halign - 1)) == 0
+		  && (unsigned int)halign != 0)
 		set_ptr_info_alignment (get_ptr_info (forcedname),
 					halign, hmisalign);
 	    }