[expr.c] PR middle-end/71700: zero-extend sub-word value when widening constructor element

	PR middle-end/71700
	* expr.c (store_constructor): Mask sign-extended bits when widening
	sub-word constructor element at the start of a word.

	* gcc.c-torture/execute/pr71700.c: New test.

From-SVN: r238248

gcc/ChangeLog

+2016-07-12  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
+
+	PR middle-end/71700
+	* expr.c (store_constructor): Mask sign-extended bits when widening
+	sub-word constructor element at the start of a word.
+
 2016-07-12  Martin Liska  <mliska@suse.cz>
 
 	* ira-build.c (mark_loops_for_removal): Properly iterate

gcc/expr.c

@@ -6281,6 +6281,13 @@ store_constructor (tree exp, rtx target, int cleared, HOST_WIDE_INT size,
 		    type = lang_hooks.types.type_for_mode
 		      (word_mode, TYPE_UNSIGNED (type));
 		    value = fold_convert (type, value);
+		    /* Make sure the bits beyond the original bitsize are zero
+		       so that we can correctly avoid extra zeroing stores in
+		       later constructor elements.  */
+		    tree bitsize_mask
+		      = wide_int_to_tree (type, wi::mask (bitsize, false,
+							   BITS_PER_WORD));
+		    value = fold_build2 (BIT_AND_EXPR, type, value, bitsize_mask);
 		  }
 
 		if (BYTES_BIG_ENDIAN)

gcc/testsuite/ChangeLog

+2016-07-12  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
+
+	PR middle-end/71700
+	* gcc.c-torture/execute/pr71700.c: New test.
+
 2016-07-12  Steven Bosscher  <steven@gcc.gnu.org>
 	Richard Biener  <rguenther@suse.de>
 

gcc/testsuite/gcc.c-torture/execute/pr71700.c

+struct S
+{
+  signed f0 : 16;
+  unsigned f1 : 1;
+};
+
+int b;
+static struct S c[] = {{-1, 0}, {-1, 0}};
+struct S d;
+
+int
+main ()
+{
+  struct S e = c[0];
+  d = e;
+  if (d.f1 != 0)
+    __builtin_abort ();
+  return 0;
+}