Adel Prokurov (Nov 05 2025 at 14:24): Adel Prokurov (Nov 05 2025 at 14:24):Hello! I found out that jo is not emitted on X86 for overflowing ops:
415c: f7 ef imul %edi
415e: 49 89 fc mov %rdi,%r12
4161: 0f 90 c1 seto %cl
4164: 84 c9 test %cl,%cl
4166: 0f 85 15 02 00 00 jne 4381 <fn0:fac:(main)_fac+0x391>
It's emitted from this code:
let (result, ovf) = ssa.builder.ins().smul_overflow(lhs, rhs);
let succ = ssa.builder.create_block();
ssa.builder.append_block_param(succ, types::I32);
ssa.builder
.ins()
.brif(ovf, slow, &[], succ, &[BlockArg::Value(result)]);
ssa.builder.switch_to_block(succ);
ssa.builder.block_params(succ)[0]
Yes this is known to have suboptimal codegen at this time, so this is not unexpected at least. That being said it's something that we'd like to improve nonetheless!
Last updated: Dec 06 2025 at 06:05 UTC