https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115703
--- Comment #5 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Robin Dapp <rd...@gcc.gnu.org>: https://gcc.gnu.org/g:44d4a1086d965fb5280daf65c7c4a253ad6cc8a1 commit r15-7608-g44d4a1086d965fb5280daf65c7c4a253ad6cc8a1 Author: Robin Dapp <rd...@ventanamicro.com> Date: Thu Feb 6 14:43:17 2025 +0100 RISC-V: Fix ratio in vsetvl fuse rule [PR115703]. In PR115703 we fuse two vsetvls: Fuse curr info since prev info compatible with it: prev_info: VALID (insn 438, bb 2) Demand fields: demand_ge_sew demand_non_zero_avl SEW=32, VLMUL=m1, RATIO=32, MAX_SEW=64 TAIL_POLICY=agnostic, MASK_POLICY=agnostic AVL=(reg:DI 0 zero) VL=(reg:DI 9 s1 [312]) curr_info: VALID (insn 92, bb 20) Demand fields: demand_ratio_and_ge_sew demand_avl SEW=64, VLMUL=m1, RATIO=64, MAX_SEW=64 TAIL_POLICY=agnostic, MASK_POLICY=agnostic AVL=(const_int 4 [0x4]) VL=(nil) prev_info after fused: VALID (insn 438, bb 2) Demand fields: demand_ratio_and_ge_sew demand_avl SEW=64, VLMUL=mf2, RATIO=64, MAX_SEW=64 TAIL_POLICY=agnostic, MASK_POLICY=agnostic AVL=(const_int 4 [0x4]) VL=(nil). The result is vsetvl zero, zero, e64, mf2, ta, ma. The previous vsetvl set vl = 4 but here we wrongly set it to vl = 2. As all the following vsetvls only ever change the ratio we never recover. The issue is quite difficult to trigger because we can often deduce the value of d at runtime. Then very check for the value of d will be optimized away. The last known bad commit is r15-3458-g5326306e7d9d36. With that commit the output is wrong but -fno-schedule-insns makes it correct. From the next commit on the issue is latent. I still added the PR's test as scan and run check even if they don't trigger right now. Not sure if the run test will ever fail but well. I verified that the patch fixes the issue when applied on top of r15-3458-g5326306e7d9d36. PR target/115703 gcc/ChangeLog: * config/riscv/riscv-vsetvl.cc: Use max_sew for calculating the new LMUL. gcc/testsuite/ChangeLog: * gcc.target/riscv/rvv/autovec/pr115703-run.c: New test. * gcc.target/riscv/rvv/autovec/pr115703.c: New test.
