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This new selftest demonstrates the improvement of bounds refinement from the previous patch. It is inspired from a set of reg_bounds_sync inputs generated using CBMC [1] by Shung-Hsi: reg.smin_value=0x8000000000000002 reg.smax_value=2 reg.umin_value=2 reg.umax_value=19 reg.s32_min_value=2 reg.s32_max_value=3 reg.u32_min_value=2 reg.u32_max_value=3 reg_bounds_sync returns R=[2; 3] without the previous patch, and R=2 with it. __reg64_deduce_bounds is able to derive that u64=2, but before the previous patch, those bounds are overwritten in __reg_deduce_mixed_bounds using the 32bits bounds. To arrive to these reg_bounds_sync inputs, we bound the 32bits value first to [2; 3]. We can then upper-bound s64 without impacting u64. At that point, the refinement to u64=2 doesn't happen because the ranges still overlap in two points: 0 umin=2 umax=0xff..ff00..03 U64_MAX | [xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx] | |----------------------------|------------------------------| |xx] [xxxxxxxxxxxxxxxxxxxxxxxxxxxx| 0 smax=2 smin=0x800..02 -1 With an upper-bound check at value 19, we can reach the above inputs for reg_bounds_sync. At that point, the refinement to u64=2 happens and because it isn't overwritten by __reg_deduce_mixed_bounds anymore, reg_bounds_sync returns with reg=2. The test validates this result by including an illegal instruction in the (dead) branch reg != 2. Link: https://github.com/shunghsiyu/reg_bounds_sync-review/ [1] Co-developed-by: Shung-Hsi Yu <shung-hsi.yu@suse.com> Signed-off-by: Shung-Hsi Yu <shung-hsi.yu@suse.com> Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com> Tested-by: Eduard Zingerman <eddyz87@gmail.com> Link: https://lore.kernel.org/r/622dc51c581cd4d652fff362188b2a5f73c1fe99.1773401138.git.paul.chaignon@gmail.com Signed-off-by: Alexei Starovoitov <ast@kernel.org>