tree-optimization/95487 - use a truth type for scatter masks

This makes sure to get a truth type for scatter masks even when they
are invariant.

2020-06-03  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/95487
	* tree-vect-stmts.c (vectorizable_store): Use a truth type
	for the scatter mask.

	* g++.dg/vect/pr95487.cc: New testcase.

gcc/testsuite/g++.dg/vect/pr95487.cc

+// { dg-do compile }
+// { dg-additional-options "-O3" }
+// { dg-additional-options "-march=skylake-avx512" { target x86_64-*-* i?86-*-* } }
+
+int a;
+bool d;
+char e;
+extern short f[];
+extern int g[];
+short j;
+void h() {
+  for (short b = j; b < 0; b += 2) {
+    f[b] = 0;
+    if (d) {
+      for (char c = 0; c < a; c += 3)
+        e = 0;
+      g[b] = 0;
+    }
+  }
+}

gcc/tree-vect-stmts.c

@@ -7643,8 +7643,12 @@ vectorizable_store (stmt_vec_info stmt_info, gimple_stmt_iterator *gsi,
 	      op = vec_oprnd0 = vect_get_vec_def_for_operand (gs_info.offset,
 							      stmt_info);
 	      if (mask)
-		mask_op = vec_mask = vect_get_vec_def_for_operand (mask,
-								   stmt_info);
+		{
+		  tree mask_vectype = truth_type_for (vectype);
+		  mask_op = vec_mask
+		    = vect_get_vec_def_for_operand (mask,
+						    stmt_info, mask_vectype);
+		}
 	    }
 	  else if (modifier != NONE && (j & 1))
 	    {