shift_to_zero: silence some warnings inside macros

There are a bunch of macros that do deliberate shifts to zero depending on
the .config.  Silence these warnings.

I'm not sure how practical and maintainable this check is...  It's
interesting to run it in private but I'm surprised I ever published this.

Signed-off-by: Dan Carpenter <[email protected]>

check_shift_to_zero.c

@@ -45,6 +45,7 @@ static void match_binop2(struct expression *expr)
 	struct expression *left;
 	struct expression *tmp;
 	sval_t mask, shift;
+	char *macro, *inner;
 
 	if (expr->op != SPECIAL_RIGHTSHIFT)
 		return;
@@ -64,7 +65,20 @@ static void match_binop2(struct expression *expr)
 	if (mask.uvalue >> shift.uvalue)
 		return;
 
-	sm_warning("mask and shift to zero");
+	macro = get_macro_name(expr->pos);
+	inner = get_inner_macro(expr->pos);
+	if (macro && inner) {
+		if (strcmp(macro, "unlikely") == 0)
+			goto warn;
+		if (strcmp(inner, "unlikely") == 0 ||
+		    strcmp(inner, "__const_hweight8") == 0 ||
+		    strcmp(inner, "BITS_PER_LONG") == 0 ||
+		    strcmp(inner, "CORDIC_PRECISION_SHIFT") == 0)
+			return;
+	}
+
+warn:
+	sm_warning("mask and shift to zero: expr='%s'", expr_to_str(expr));
 }
 
 static void match_assign(struct expression *expr)