rustc --crate-type=lib -O main.rs --emit=llvm-ir

rust.ll

; ModuleID = 'main0-8787f43e282added376259c1adb08b80.rs'
source_filename = "main0-8787f43e282added376259c1adb08b80.rs"
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

%"unwind::libunwind::_Unwind_Exception" = type { [0 x i64], i64, [0 x i64], void (i32, %"unwind::libunwind::_Unwind_Exception"*)*, [0 x i64], [6 x i64], [0 x i64] }
%"unwind::libunwind::_Unwind_Context" = type { [0 x i8] }

; main::return_option
; Function Attrs: norecurse nounwind readnone uwtable
define { i64, i64 } @_ZN4main13return_option17h753bafe80c73e49fE(i64 %x) unnamed_addr #0 {
start:
  %0 = icmp slt i64 %x, 32
  %1 = srem i64 %x, 752
  %_0.sroa.0.0 = zext i1 %0 to i64
  %2 = insertvalue { i64, i64 } undef, i64 %_0.sroa.0.0, 0
  %3 = insertvalue { i64, i64 } %2, i64 %1, 1
  ret { i64, i64 } %3
}

; main::foo
; Function Attrs: norecurse nounwind readnone uwtable
define i64 @_ZN4main3foo17h4446f8db1af5d6d1E(i64 %x) unnamed_addr #0 personality i32 (i32, i32, i64, %"unwind::libunwind::_Unwind_Exception"*, %"unwind::libunwind::_Unwind_Context"*)* @rust_eh_personality {
start:
  %0 = icmp sgt i64 %x, 31
  %1 = srem i64 %x, 752
  %..i = select i1 %0, i64 17, i64 %1
  %2 = add i64 %..i, %x
  ret i64 %2
}

declare i32 @rust_eh_personality(i32, i32, i64, %"unwind::libunwind::_Unwind_Exception"*, %"unwind::libunwind::_Unwind_Context"*) unnamed_addr #1

attributes #0 = { norecurse nounwind readnone uwtable "probe-stack"="__rust_probestack" }
attributes #1 = { "probe-stack"="__rust_probestack" }