selftests/bpf: Add reg_bounds tests for ldsx and subreg compare

Add a few reg_bounds selftests to test 32/16/8-bit ldsx and subreg comparison.
Without the previous patch, all added tests will fail.
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20240723162940.2732171-1-yonghong.song@linux.devSigned-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>

tools/testing/selftests/bpf/prog_tests/reg_bounds.c

@@ -433,6 +433,19 @@ static struct range range_refine(enum num_t x_t, struct range x, enum num_t y_t,
 
 	y_cast = range_cast(y_t, x_t, y);
 
+	/* If we know that
+	 *   - *x* is in the range of signed 32bit value, and
+	 *   - *y_cast* range is 32-bit signed non-negative
+	 * then *x* range can be improved with *y_cast* such that *x* range
+	 * is 32-bit signed non-negative. Otherwise, if the new range for *x*
+	 * allows upper 32-bit * 0xffffffff then the eventual new range for
+	 * *x* will be out of signed 32-bit range which violates the origin
+	 * *x* range.
+	 */
+	if (x_t == S64 && y_t == S32 && y_cast.a <= S32_MAX  && y_cast.b <= S32_MAX &&
+	    (s64)x.a >= S32_MIN && (s64)x.b <= S32_MAX)
+		return range_improve(x_t, x, y_cast);
+
 	/* the case when new range knowledge, *y*, is a 32-bit subregister
 	 * range, while previous range knowledge, *x*, is a full register
 	 * 64-bit range, needs special treatment to take into account upper 32
@@ -2108,6 +2121,9 @@ static struct subtest_case crafted_cases[] = {
 	{S32, U32, {(u32)S32_MIN, 0}, {0, 0}},
 	{S32, U32, {(u32)S32_MIN, 0}, {(u32)S32_MIN, (u32)S32_MIN}},
 	{S32, U32, {(u32)S32_MIN, S32_MAX}, {S32_MAX, S32_MAX}},
+	{S64, U32, {0x0, 0x1f}, {0xffffffff80000000ULL, 0x000000007fffffffULL}},
+	{S64, U32, {0x0, 0x1f}, {0xffffffffffff8000ULL, 0x0000000000007fffULL}},
+	{S64, U32, {0x0, 0x1f}, {0xffffffffffffff80ULL, 0x000000000000007fULL}},
 };
 
 /* Go over crafted hard-coded cases. This is fast, so we do it as part of