https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112326
--- Comment #1 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Pan Li <pa...@gcc.gnu.org>: https://gcc.gnu.org/g:5ea3c039b784b0676323243940fd9916b1f6d540 commit r14-5092-g5ea3c039b784b0676323243940fd9916b1f6d540 Author: Juzhe-Zhong <juzhe.zh...@rivai.ai> Date: Fri Nov 3 08:36:03 2023 +0800 RISC-V: Fix redundant vsetvl in fixed-vlmax vectorized codes[PR112326] With compile option --param=riscv-autovec-preference=fixed-vlmax, we have redundant AVL/VL toggling: vsetvli a5,a3,e8,mf4,ta,ma -> should be changed into e32m1 vle32.v v1,0(a1) vle32.v v2,0(a0) vsetivli zero,4,e32,m1,ta,ma -> redundant slli a2,a5,2 vadd.vv v1,v1,v2 sub a3,a3,a5 vsetvli zero,a5,e32,m1,ta,ma -> redundant vse32.v v1,0(a4) add a0,a0,a2 add a1,a1,a2 add a4,a4,a2 bne a3,zero,.L3 The root cause is because we simplify AVL into immediate AVL too early in FIXED-VLMAX situation. The later avlprop PASS failed to propagate AVL generated by (SELECT_VL/vsetvl VL, AVL) into the normal RVV instruction. So we need to remove immedate AVL simplification in 'expand' stage. After this patch: vsetvli a5,a3,e32,m1,ta,ma slli a2,a5,2 vle32.v v1,0(a1) vle32.v v2,0(a0) sub a3,a3,a5 vadd.vv v1,v1,v2 vse32.v v1,0(a4) add a0,a0,a2 add a1,a1,a2 add a4,a4,a2 bne a3,zero,.L3 After the removed simplification, the following situation should be fixed: typedef int8_t vnx2qi __attribute__ ((vector_size (2))); __attribute__ ((noipa)) void f_vnx2qi (int8_t a, int8_t b, int8_t *out) { vnx2qi v = {a, b}; *(vnx2qi *) out = v; } We should use vsetvili zero, 2 instead of vsetvl a5,zero. Such simplification is done in avlprop PASS which is also included in this patch to fix regression of these situation. PR target/112326 gcc/ChangeLog: * config/riscv/riscv-avlprop.cc (get_insn_vtype_mode): New function. (simplify_replace_vlmax_avl): Ditto. (pass_avlprop::execute): Add immediate AVL simplification. * config/riscv/riscv-protos.h (imm_avl_p): Rename. * config/riscv/riscv-v.cc (const_vlmax_p): Ditto. (imm_avl_p): Ditto. (emit_vlmax_insn): Adapt for new interface name. * config/riscv/vector.md (mode_idx): New attribute. gcc/testsuite/ChangeLog: * gcc.target/riscv/rvv/autovec/pr112326.c: New test.
