The result of a shift operation on a constants by a constant value is
also constant.
Found through a false positive VLA detected in the Linux kernel.
The array size was computed through min() on a shifted constant value
and sparse complained about it.
Signed-off-by: Thomas Weißschuh <thomas@xxxxxxxx>
---
expand.c | 2 +-
validation/simplify-binops.c | 12 ++++++++++++
2 files changed, 13 insertions(+), 1 deletion(-)
create mode 100644 validation/simplify-binops.c
diff --git a/expand.c b/expand.c
index e8e50b0..7936e29 100644
--- a/expand.c
+++ b/expand.c
@@ -197,7 +197,7 @@ static int simplify_int_binop(struct expression *expr, struct symbol *ctype)
return 0;
r = right->value;
if (expr->op == SPECIAL_LEFTSHIFT || expr->op == SPECIAL_RIGHTSHIFT) {
- if (conservative)
+ if (conservative && left->type != EXPR_VALUE)
return 0;
check_shift_count(expr, right);
}
diff --git a/validation/simplify-binops.c b/validation/simplify-binops.c
new file mode 100644
index 0000000..e464c37
--- /dev/null
+++ b/validation/simplify-binops.c
@@ -0,0 +1,12 @@
+#define __is_constexpr(x) \
+ (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
+
+static void test(int x) {
+ static int b[] = {
+ [__builtin_choose_expr(__is_constexpr(1 << 1), 1, x)] = 0,
+ };
+}
+
+/*
+ * check-name: simplify-binops
+ */
--
2.21.0
