[PATCH] bitops: add compile-time test for ror() and rol()

[Yury Norov]

If parameters for the functions are passed at compile time, the compiler
must calculate the result at compile time, as well.

Now that architectures introduce accelerated implementations for bit
rotation, we must make sure that they don't break compile-time
evaluation.

This patch adds a test for it, similarly to test_bitmap_const_eval().

Tested on x86_64.

Signed-off-by: Yury Norov (NVIDIA) <yury.norov@xxxxxxxxx>
---
 lib/test_bitops.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/lib/test_bitops.c b/lib/test_bitops.c
index 55669624bb28..aa4c06df34f7 100644
--- a/lib/test_bitops.c
+++ b/lib/test_bitops.c
@@ -76,6 +76,56 @@ static int __init test_fns(void)
 	return 0;
 }
 
+static void __init test_bitops_const_eval(void)
+{
+	/*
+	 * ror/rol operations on parameters known at compile-time must be
+	 * optimized to compile-time constants on any supported optimization
+	 * level (-O2, -Os) and all architectures. Otherwise, trigger a build
+	 * bug.
+	 */
+
+	u64 r64 = ror64(0x1234567890abcdefull, 24);
+
+	BUILD_BUG_ON(!__builtin_constant_p(r64));
+	BUILD_BUG_ON(r64 != 0xabcdef1234567890ull);
+
+	u64 l64 = rol64(0x1234567890abcdefull, 24);
+
+	BUILD_BUG_ON(!__builtin_constant_p(l64));
+	BUILD_BUG_ON(l64 != 0x7890abcdef123456ull);
+
+	u32 r32 = ror32(0x12345678, 24);
+
+	BUILD_BUG_ON(!__builtin_constant_p(r32));
+	BUILD_BUG_ON(r32 != 0x34567812);
+
+	u32 l32 = rol32(0x12345678, 24);
+
+	BUILD_BUG_ON(!__builtin_constant_p(l32));
+	BUILD_BUG_ON(l32 != 0x78123456);
+
+	u16 r16 = ror16(0x1234, 12);
+
+	BUILD_BUG_ON(!__builtin_constant_p(r16));
+	BUILD_BUG_ON(r16 != 0x2341);
+
+	u16 l16 = rol16(0x1234, 12);
+
+	BUILD_BUG_ON(!__builtin_constant_p(l16));
+	BUILD_BUG_ON(l16 != 0x4123);
+
+	u8 r8 = ror8(0x12, 6);
+
+	BUILD_BUG_ON(!__builtin_constant_p(r16));
+	BUILD_BUG_ON(r8 != 0x48);
+
+	u8 l8 = rol8(0x12, 6);
+
+	BUILD_BUG_ON(!__builtin_constant_p(l16));
+	BUILD_BUG_ON(l8 != 0x84);
+}
+
 static int __init test_bitops_startup(void)
 {
 	int i, bit_set;
@@ -121,6 +171,7 @@ static int __init test_bitops_startup(void)
 		pr_err("ERROR: FOUND SET BIT %d\n", bit_set);
 
 	test_fns();
+	test_bitops_const_eval();
 
 	pr_info("Completed bitops test\n");
 
-- 
2.43.0