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authorAlexander Lobakin <alexandr.lobakin@intel.com>2022-06-24 14:13:13 +0200
committerYury Norov <yury.norov@gmail.com>2022-06-30 19:52:42 -0700
commitdc34d5036692c614eef23c1130ee42a201c316bf (patch)
tree8dc42f556d9169303817bc01628478d79a7507b6
parent3e7e5baaaba78075a7f3a57432609e363bf2a486 (diff)
lib: test_bitmap: add compile-time optimization/evaluations assertions
Add a function to the bitmap test suite, which will ensure that compilers are able to evaluate operations performed by the bitops/bitmap helpers to compile-time constants when all of the arguments are compile-time constants as well, or trigger a build bug otherwise. This should work on all architectures and all the optimization levels supported by Kbuild. The function doesn't perform any runtime tests and gets optimized out to nothing after passing the build assertions. Unfortunately, Clang for s390 is currently broken (up to the latest Git snapshots) -- see the comment in the code -- so for now there's a small workaround for it which doesn't alter the logics. Hope we'll be able to remove it one day (bugreport is on its way). Suggested-by: Yury Norov <yury.norov@gmail.com> Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Signed-off-by: Yury Norov <yury.norov@gmail.com>
-rw-r--r--lib/test_bitmap.c62
1 files changed, 62 insertions, 0 deletions
diff --git a/lib/test_bitmap.c b/lib/test_bitmap.c
index d5923a640457..25967cfa4ab2 100644
--- a/lib/test_bitmap.c
+++ b/lib/test_bitmap.c
@@ -869,6 +869,67 @@ static void __init test_bitmap_print_buf(void)
}
}
+static void __init test_bitmap_const_eval(void)
+{
+ DECLARE_BITMAP(bitmap, BITS_PER_LONG);
+ unsigned long initvar = BIT(2);
+ unsigned long bitopvar = 0;
+ unsigned long var = 0;
+ int res;
+
+ /*
+ * Compilers must be able to optimize all of those to compile-time
+ * constants on any supported optimization level (-O2, -Os) and any
+ * architecture. Otherwise, trigger a build bug.
+ * The whole function gets optimized out then, there's nothing to do
+ * in runtime.
+ */
+
+ /*
+ * Equals to `unsigned long bitmap[1] = { GENMASK(6, 5), }`.
+ * Clang on s390 optimizes bitops at compile-time as intended, but at
+ * the same time stops treating @bitmap and @bitopvar as compile-time
+ * constants after regular test_bit() is executed, thus triggering the
+ * build bugs below. So, call const_test_bit() there directly until
+ * the compiler is fixed.
+ */
+ bitmap_clear(bitmap, 0, BITS_PER_LONG);
+#if defined(__s390__) && defined(__clang__)
+ if (!const_test_bit(7, bitmap))
+#else
+ if (!test_bit(7, bitmap))
+#endif
+ bitmap_set(bitmap, 5, 2);
+
+ /* Equals to `unsigned long bitopvar = BIT(20)` */
+ __change_bit(31, &bitopvar);
+ bitmap_shift_right(&bitopvar, &bitopvar, 11, BITS_PER_LONG);
+
+ /* Equals to `unsigned long var = BIT(25)` */
+ var |= BIT(25);
+ if (var & BIT(0))
+ var ^= GENMASK(9, 6);
+
+ /* __const_hweight<32|64>(GENMASK(6, 5)) == 2 */
+ res = bitmap_weight(bitmap, 20);
+ BUILD_BUG_ON(!__builtin_constant_p(res));
+ BUILD_BUG_ON(res != 2);
+
+ /* !(BIT(31) & BIT(18)) == 1 */
+ res = !test_bit(18, &bitopvar);
+ BUILD_BUG_ON(!__builtin_constant_p(res));
+ BUILD_BUG_ON(!res);
+
+ /* BIT(2) & GENMASK(14, 8) == 0 */
+ res = initvar & GENMASK(14, 8);
+ BUILD_BUG_ON(!__builtin_constant_p(res));
+ BUILD_BUG_ON(res);
+
+ /* ~BIT(25) */
+ BUILD_BUG_ON(!__builtin_constant_p(~var));
+ BUILD_BUG_ON(~var != ~BIT(25));
+}
+
static void __init selftest(void)
{
test_zero_clear();
@@ -884,6 +945,7 @@ static void __init selftest(void)
test_for_each_set_clump8();
test_bitmap_cut();
test_bitmap_print_buf();
+ test_bitmap_const_eval();
}
KSTM_MODULE_LOADERS(test_bitmap);