re PR middle-end/91131 (Bad bitfield coalescing)

2019-07-11  Richard Biener  <rguenther@suse.de>

	PR middle-end/91131
	* gimplify.c (gimplify_compound_literal_expr): Force a temporary
	when the object is volatile and we have not cleared it even though
	there are no nonzero elements.

	* gcc.target/i386/pr91131.c: New testcase.

From-SVN: r273376

gcc/ChangeLog

+2019-07-11  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/91131
+	* gimplify.c (gimplify_compound_literal_expr): Force a temporary
+	when the object is volatile and we have not cleared it even though
+	there are no nonzero elements.
+
 2019-07-10  Michael Meissner  <meissner@linux.ibm.com>
 
 	* config/rs6000/predicates.md (cint34_operand): Update

gcc/gimplify.c

@@ -5005,7 +5005,7 @@ gimplify_init_constructor (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p,
 	   one field to assign, initialize the target from a temporary.  */
 	if (TREE_THIS_VOLATILE (object)
 	    && !TREE_ADDRESSABLE (type)
-	    && num_nonzero_elements > 0
+	    && (num_nonzero_elements > 0 || !cleared)
 	    && vec_safe_length (elts) > 1)
 	  {
 	    tree temp = create_tmp_var (TYPE_MAIN_VARIANT (type));

gcc/testsuite/ChangeLog

+2019-07-11  Richard Biener  <rguenther@suse.de>
+
+	PR middle-end/91131
+	* gcc.target/i386/pr91131.c: New testcase.
+
 2019-07-10  Martin Sebor  <msebor@redhat.com>
 
 	PR testsuite/91132

gcc/testsuite/gcc.target/i386/pr91131.c

+/* { dg-do compile } */
+/* { dg-options "-O" } */
+
+struct Reg_T {
+    unsigned int a : 3;
+    unsigned int b : 1;
+    unsigned int c : 4;
+};
+
+volatile struct Reg_T Reg_A;
+
+int
+main ()
+{
+  Reg_A = (struct Reg_T){ .a = 0, .b = 0, .c = 0 };
+  return 0;
+}
+
+/* { dg-final { scan-assembler-times "mov\[^\r\n\]*Reg_A" 1 } } */