https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116278
--- Comment #9 from GCC 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:e8f31f4f58f0fcf1716fc1d9ee003fbcdda600c3 commit r15-2979-ge8f31f4f58f0fcf1716fc1d9ee003fbcdda600c3 Author: Pan Li <pan2...@intel.com> Date: Fri Aug 9 10:26:32 2024 +0800 RISC-V: Make sure high bits of usadd operands is clean for non-Xmode [PR116278] For QI/HImode of .SAT_ADD, the operands may be sign-extended and the high bits of Xmode may be all 1 which is not expected. For example as below code. signed char b[1]; unsigned short c; signed char *d = b; int main() { b[0] = -40; c = ({ (unsigned short)d[0] < 0xFFF6 ? (unsigned short)d[0] : 0xFFF6; }) + 9; __builtin_printf("%d\n", c); } After expanding we have: ;; _6 = .SAT_ADD (_3, 9); (insn 8 7 9 (set (reg:DI 143) (high:DI (symbol_ref:DI ("d") [flags 0x86] <var_decl d>))) (nil)) (insn 9 8 10 (set (reg/f:DI 142) (mem/f/c:DI (lo_sum:DI (reg:DI 143) (symbol_ref:DI ("d") [flags 0x86] <var_decl d>)) [1 d+0 S8 A64])) (nil)) (insn 10 9 11 (set (reg:HI 144 [ _3 ]) (sign_extend:HI (mem:QI (reg/f:DI 142) [0 *d.0_1+0 S1 A8]))) "test.c":7:10 -1 (nil)) The convert from signed char to unsigned short will have sign_extend rtl as above. And finally become the lb insn as below: lb a1,0(a5) // a1 is -40, aka 0xffffffffffffffd8 lui a0,0x1a addi a5,a1,9 slli a5,a5,0x30 srli a5,a5,0x30 // a5 is 65505 sltu a1,a5,a1 // compare 65505 and 0xffffffffffffffd8 => TRUE The sltu try to compare 65505 and 0xffffffffffffffd8 here, but we actually want to compare 65505 and 65496 (0xffd8). Thus we need to clean up the high bits to ensure this. The below test suites are passed for this patch: * The rv64gcv fully regression test. PR target/116278 gcc/ChangeLog: * config/riscv/riscv.cc (riscv_gen_zero_extend_rtx): Add new func impl to zero extend rtx. (riscv_expand_usadd): Leverage above func to cleanup operands 0 and remove the special handing for SImode in RV64. gcc/testsuite/ChangeLog: * gcc.target/riscv/sat_u_add-11.c: Adjust asm check body. * gcc.target/riscv/sat_u_add-15.c: Ditto. * gcc.target/riscv/sat_u_add-19.c: Ditto. * gcc.target/riscv/sat_u_add-23.c: Ditto. * gcc.target/riscv/sat_u_add-3.c: Ditto. * gcc.target/riscv/sat_u_add-7.c: Ditto. * gcc.target/riscv/sat_u_add_imm-11.c: Ditto. * gcc.target/riscv/sat_u_add_imm-15.c: Ditto. * gcc.target/riscv/sat_u_add_imm-3.c: Ditto. * gcc.target/riscv/sat_u_add_imm-7.c: Ditto. * gcc.target/riscv/pr116278-run-1.c: New test. * gcc.target/riscv/pr116278-run-2.c: New test. Signed-off-by: Pan Li <pan2...@intel.com>
