https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116256
--- Comment #5 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jeff Law <l...@gcc.gnu.org>: https://gcc.gnu.org/g:61995d86b66b39698c0dfbbab8d8dca579b42d00 commit r15-7100-g61995d86b66b39698c0dfbbab8d8dca579b42d00 Author: Jeff Law <j...@ventanamicro.com> Date: Tue Jan 21 06:56:27 2025 -0700 [RISC-V][PR target/116256] Fix incorrect return value for predicate Another bug found while chasing paths to fix the remaining issues in pr116256. This case is sometimes benign when the optimizers are enabled. But could show up in a -O0 compile with some patterns I was playing around with. Basically we have a predicate that is meant to return true if bits set in the operand are all consecutive. That predicate would return the wrong value when presented with (const_int 0) indicating it had a run of on bits when obviously no bits are on ð It's pretty obvious once you look at the implementation. if (exact_log2 ((val >> ctz_hwi (val)) + 1) < 0) return false return true; The right shift is always going to produce 0. 0 + 1 = 1 which is a power of 2. So exact_log2 returns 0 and we get a true result rather than a false result. The fix is trivial. "<=". While inside we might as well fix the formatting. Tested on rv32 and rv64 in my tester. Waiting on upstream pre-commit testing to render a verdict. PR target/116256 gcc/ * config/riscv/predicates.md (consecutive_bits_operand): Properly handle (const_int 0).
