middle-end/101530 - fix shufflevector lowering

This makes __builtin_shufflevector lowering force the result
of the BIT_FIELD_REF lowpart operation to a temporary as to
fulfil the IL verifier constraint that BIT_FIELD_REFs should
be always in outermost handled component position.  Trying to
enforce this during gimplification isn't as straight-forward
as here where we know we're dealing with an rvalue.

FAIL: c-c++-common/torture/builtin-shufflevector-1.c   -O0  execution test

2022-01-05  Richard Biener  <rguenther@suse.de>

	PR middle-end/101530
gcc/c-family/
	* c-common.c (c_build_shufflevector): Wrap the BIT_FIELD_REF
	in a TARGET_EXPR to force a temporary.

gcc/testsuite/
	* c-c++-common/builtin-shufflevector-3.c: New testcase.

gcc/c-family/c-common.c

@@ -1243,6 +1243,13 @@ c_build_shufflevector (location_t loc, tree v0, tree v1,
       tree lpartt = build_vector_type (TREE_TYPE (ret_type), mask.length ());
       ret = build3_loc (loc, BIT_FIELD_REF,
 			lpartt, ret, TYPE_SIZE (lpartt), bitsize_zero_node);
+      /* Wrap the lowpart operation in a TARGET_EXPR so it gets a separate
+	 temporary during gimplification.  See PR101530 for cases where
+	 we'd otherwise end up with non-toplevel BIT_FIELD_REFs.  */
+      tree tem = create_tmp_var_raw (lpartt);
+      DECL_CONTEXT (tem) = current_function_decl;
+      ret = build4 (TARGET_EXPR, lpartt, tem, ret, NULL_TREE, NULL_TREE);
+      TREE_SIDE_EFFECTS (ret) = 1;
     }
 
   if (!c_dialect_cxx () && !wrap)

gcc/testsuite/c-c++-common/builtin-shufflevector-3.c

@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+
+typedef int __attribute__((__vector_size__ (sizeof(int)*4))) V;
+
+int
+foo(V v, int i)
+{
+  return __builtin_shufflevector (v, v, 2, 3)[i];
+}
+
+int
+bar(V v, int i)
+{
+  return __builtin_shufflevector(v, v, 4)[0] & i;
+}