Cranelift: Cannot create 128 bit constants

[Kixiron]

I can't figure out how to create a 128bit constant. My closest attempt was by creating a 128bit vector which I then bitcast into an i128, but that doesn't work

let constant = builder.func.dfg.constants.insert(V128Imm::from(value).into());
let vector = builder.ins().vconst(types::I64X2, constant);

let mut flags = MemFlags::new();
// Endianness is required here since I'm "changing the number of lanes" so this is my best guess for getting correct behavior?
flags.set_endianness(if cfg!(target_endian = "little") {
    Endianness::Little
} else {
    Endianness::Big
});

builder.ins().bitcast(types::I128, flags, vector)

Cranelift panics with this

thread 'codegen::vtable::tests::proptests::vtables' panicked at 'should be implemented in ISLE: inst = `v4 = bitcast.i128 little v3  ; v3 = const0`, type = `Some(types::I128)`', C:\Users\Chase\.cargo\registry\src\github.heygears.com-1ecc6299db9ec823\cranelift-codegen-0.96.4\src\machinst\lower.rs:747:21
stack backtrace:
   0:     0x7ff6532aa862 - std::backtrace_rs::backtrace::dbghelp::trace
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\..\..\backtrace\src\backtrace\dbghelp.rs:98
   1:     0x7ff6532aa862 - std::backtrace_rs::backtrace::trace_unsynchronized
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\..\..\backtrace\src\backtrace\mod.rs:66
   2:     0x7ff6532aa862 - std::sys_common::backtrace::_print_fmt
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\sys_common\backtrace.rs:65
   3:     0x7ff6532aa862 - std::sys_common::backtrace::_print::impl$0::fmt
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\sys_common\backtrace.rs:44
   4:     0x7ff6532cd36b - core::fmt::write
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\core\src\fmt\mod.rs:1208
   5:     0x7ff6532a54aa - std::io::Write::write_fmt<std::sys::windows::stdio::Stderr>
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\io\mod.rs:1682
   6:     0x7ff6532aa5ab - std::sys_common::backtrace::_print
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\sys_common\backtrace.rs:47
   7:     0x7ff6532aa5ab - std::sys_common::backtrace::print
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\sys_common\backtrace.rs:34
   8:     0x7ff6532ad6d9 - std::panicking::default_hook::closure$1
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\panicking.rs:267
   9:     0x7ff6532ad35b - std::panicking::default_hook
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\panicking.rs:286
  10:     0x7ff6532adf71 - std::panicking::rust_panic_with_hook
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\panicking.rs:688
  11:     0x7ff6532adcfe - std::panicking::begin_panic_handler::closure$0
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\panicking.rs:579
  12:     0x7ff6532ab55f - std::sys_common::backtrace::__rust_end_short_backtrace<std::panicking::begin_panic_handler::closure_env$0,never$>
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\sys_common\backtrace.rs:137
  13:     0x7ff6532ad9b0 - std::panicking::begin_panic_handler
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\panicking.rs:575
  14:     0x7ff6532da8a5 - core::panicking::panic_fmt
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\core\src\panicking.rs:64
  15:     0x7ff652ff136e - cranelift_codegen::machinst::lower::impl$3::lower_clif_block::closure$0<enum2$<cranelift_codegen::isa::x64::lower::isle::generated_code::MInst>,cranelift_codegen::isa::x64::X64Backend>
                               at C:\Users\Chase\.cargo\registry\src\github.heygears.com-1ecc6299db9ec823\cranelift-codegen-0.96.4\src\machinst\lower.rs:747
  16:     0x7ff652f3b15b - enum2$<core::option::Option<smallvec::SmallVec<array$<cranelift_codegen::machinst::valueregs::ValueRegs<cranelift_codegen::machinst::reg::Reg>,2> > > >::unwrap_or_else<smallvec::SmallVec<array$<cranelift_codegen::machinst::valueregs::ValueRegs<cranelift_c
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483\library\core\src\option.rs:828
  17:     0x7ff652ff0c41 - cranelift_codegen::machinst::lower::Lower<enum2$<cranelift_codegen::isa::x64::lower::isle::generated_code::MInst> >::lower_clif_block<enum2$<cranelift_codegen::isa::x64::lower::isle::generated_code::MInst>,cranelift_codegen::isa::x64::X64Backend>
                               at C:\Users\Chase\.cargo\registry\src\github.heygears.com-1ecc6299db9ec823\cranelift-codegen-0.96.4\src\machinst\lower.rs:741
  18:     0x7ff652ff33ed - cranelift_codegen::machinst::lower::Lower<enum2$<cranelift_codegen::isa::x64::lower::isle::generated_code::MInst> >::lower<enum2$<cranelift_codegen::isa::x64::lower::isle::generated_code::MInst>,cranelift_codegen::isa::x64::X64Backend>
                               at C:\Users\Chase\.cargo\registry\src\github.heygears.com-1ecc6299db9ec823\cranelift-codegen-0.96.4\src\machinst\lower.rs:1045
  19:     0x7ff652e7dc78 - cranelift_codegen::machinst::compile::compile<cranelift_codegen::isa::x64::X64Backend>
                               at C:\Users\Chase\.cargo\registry\src\github.heygears.com-1ecc6299db9ec823\cranelift-codegen-0.96.4\src\machinst\compile.rs:40
  20:     0x7ff652fc1f16 - cranelift_codegen::isa::x64::X64Backend::compile_vcode
                               at C:\Users\Chase\.cargo\registry\src\github.heygears.com-1ecc6299db9ec823\cranelift-codegen-0.96.4\src\isa\x64\mod.rs:61
  21:     0x7ff652fc20bc - cranelift_codegen::isa::x64::impl$1::compile_function
                               at C:\Users\Chase\.cargo\registry\src\github.heygears.com-1ecc6299db9ec823\cranelift-codegen-0.96.4\src\isa\x64\mod.rs:73
  22:     0x7ff652f5b4d4 - cranelift_codegen::context::Context::compile_stencil
                               at C:\Users\Chase\.cargo\registry\src\github.heygears.com-1ecc6299db9ec823\cranelift-codegen-0.96.4\src\context.rs:146
  23:     0x7ff652f5bef1 - cranelift_codegen::context::Context::compile
                               at C:\Users\Chase\.cargo\registry\src\github.heygears.com-1ecc6299db9ec823\cranelift-codegen-0.96.4\src\context.rs:206
  24:     0x7ff652dcbe72 - cranelift_jit::backend::impl$2::define_function_with_control_plane
                               at C:\Users\Chase\.cargo\registry\src\github.heygears.com-1ecc6299db9ec823\cranelift-jit-0.96.4\src\backend.rs:689
  25:     0x7ff651ee1b34 - cranelift_module::module::Module::define_function<cranelift_jit::backend::JITModule>
                               at C:\Users\Chase\.cargo\registry\src\github.heygears.com-1ecc6299db9ec823\cranelift-module-0.96.4\src\module.rs:919
  26:     0x7ff651f187a6 - dataflow_jit::codegen::Codegen::finalize_function
                               at G:\Users\Chase\Code\Rust\dbsp\crates\dataflow-jit\src\codegen\mod.rs:482
  27:     0x7ff651f156db - dataflow_jit::codegen::Codegen::codegen_layout_default
                               at G:\Users\Chase\Code\Rust\dbsp\crates\dataflow-jit\src\codegen\vtable\default.rs:148
  28:     0x7ff651f43f35 - dataflow_jit::codegen::Codegen::make_vtable_for
                               at G:\Users\Chase\Code\Rust\dbsp\crates\dataflow-jit\src\codegen\vtable\mod.rs:113
  29:     0x7ff651f43d11 - dataflow_jit::codegen::Codegen::vtable_for
                               at G:\Users\Chase\Code\Rust\dbsp\crates\dataflow-jit\src\codegen\vtable\mod.rs:92
  30:     0x7ff6522ab963 - dataflow_jit::codegen::vtable::tests::proptests::test_layout
                               at G:\Users\Chase\Code\Rust\dbsp\crates\dataflow-jit\src\codegen\vtable\tests.rs:702
  31:     0x7ff651edc1bb - dataflow_jit::codegen::vtable::tests::proptests::vtables::closure$1
                               at G:\Users\Chase\Code\Rust\dbsp\crates\dataflow-jit\src\codegen\vtable\tests.rs:801
  32:     0x7ff651edb2c1 - core::ops::function::impls::impl$0::call<tuple$<proptest::sugar::NamedArguments<ref$<str$>,dataflow_jit::codegen::vtable::tests::proptests::PropLayout> >,dataflow_jit::codegen::vtable::tests::proptests::vtables::closure_env$1>
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483\library\core\src\ops\function.rs:582
  33:     0x7ff652616ec8 - proptest::test_runner::runner::call_test::closure$3<proptest::sugar::NamedArguments<ref$<str$>,dataflow_jit::codegen::vtable::tests::proptests::PropLayout>,ref$<dataflow_jit::codegen::vtable::tests::proptests::vtables::closure_env$1>,alloc::vec::into_iter
                               at C:\Users\Chase\.cargo\registry\src\github.heygears.com-1ecc6299db9ec823\proptest-1.2.0\src\test_runner\runner.rs:254
  34:     0x7ff6523f6acd - core::panic::unwind_safe::impl$23::call_once<enum2$<core::result::Result<tuple$<>,enum2$<proptest::test_runner::errors::TestCaseError> > >,proptest::test_runner::runner::call_test::closure_env$3<proptest::sugar::NamedArguments<ref$<str$>,dataflow_jit::cod
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483\library\core\src\panic\unwind_safe.rs:271
  35:     0x7ff65240d315 - std::panicking::try::do_call<core::panic::unwind_safe::AssertUnwindSafe<proptest::test_runner::runner::call_test::closure_env$3<proptest::sugar::NamedArguments<ref$<str$>,dataflow_jit::codegen::vtable::tests::proptests::PropLayout>,ref$<dataflow_jit::code
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483\library\std\src\panicking.rs:483
  36:     0x7ff652411803 - std::panicking::try::do_catch<core::panic::unwind_safe::AssertUnwindSafe<std::thread::impl$0::spawn_unchecked_::closure$1::closure_env$0<dbsp::circuit::runtime::impl$5::run::closure$0::closure_env$0<dbsp::circuit::dbsp_handle::impl$0::init_circuit::closur
  37:     0x7ff652403451 - std::panicking::try<enum2$<core::result::Result<tuple$<>,enum2$<proptest::test_runner::errors::TestCaseError> > >,core::panic::unwind_safe::AssertUnwindSafe<proptest::test_runner::runner::call_test::closure_env$3<proptest::sugar::NamedArguments<ref$<str$>
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483\library\std\src\panicking.rs:447
  38:     0x7ff65231033d - std::panic::catch_unwind<core::panic::unwind_safe::AssertUnwindSafe<proptest::test_runner::runner::call_test::closure_env$3<proptest::sugar::NamedArguments<ref$<str$>,dataflow_jit::codegen::vtable::tests::proptests::PropLayout>,ref$<dataflow_jit::codegen:
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483\library\std\src\panic.rs:137
  39:     0x7ff6525ebbec - proptest::test_runner::runner::call_test<proptest::sugar::NamedArguments<ref$<str$>,dataflow_jit::codegen::vtable::tests::proptests::PropLayout>,ref$<dataflow_jit::codegen::vtable::tests::proptests::vtables::closure_env$1>,alloc::vec::into_iter::IntoIter<
                               at C:\Users\Chase\.cargo\registry\src\github.heygears.com-1ecc6299db9ec823\proptest-1.2.0\src\test_runner\runner.rs:254
  40:     0x7ff65255d648 - proptest::test_runner::runner::TestRunner::run_one_with_replay<proptest::strategy::map::Map<proptest::strategy::map::Map<proptest::collection::VecValueTree<proptest::strategy::unions::TupleUnionValueTree<tuple$<proptest::strategy::lazy::LazyValueTree<prop
                               at C:\Users\Chase\.cargo\registry\src\github.heygears.com-1ecc6299db9ec823\proptest-1.2.0\src\test_runner\runner.rs:726
  41:     0x7ff65253c557 - proptest::test_runner::runner::TestRunner::gen_and_run_case<proptest::strategy::map::Map<proptest::strategy::map::Map<proptest::collection::VecStrategy<proptest::strategy::unions::TupleUnion<tuple$<tuple$<u32,alloc::sync::Arc<proptest::strategy::map::Map<
                               at C:\Users\Chase\.cargo\registry\src\github.heygears.com-1ecc6299db9ec823\proptest-1.2.0\src\test_runner\runner.rs:668
  42:     0x7ff65258ab56 - proptest::test_runner::runner::TestRunner::run_in_process_with_replay<proptest::strategy::map::Map<proptest::strategy::map::Map<proptest::collection::VecStrategy<proptest::strategy::unions::TupleUnion<tuple$<tuple$<u32,alloc::sync::Arc<proptest::strategy:
                               at C:\Users\Chase\.cargo\registry\src\github.heygears.com-1ecc6299db9ec823\proptest-1.2.0\src\test_runner\runner.rs:602
  43:     0x7ff65252b0e6 - proptest::test_runner::runner::TestRunner::run_in_process<proptest::strategy::map::Map<proptest::strategy::map::Map<proptest::collection::VecStrategy<proptest::strategy::unions::TupleUnion<tuple$<tuple$<u32,alloc::sync::Arc<proptest::strategy::map::Map<pr
                               at C:\Users\Chase\.cargo\registry\src\github.heygears.com-1ecc6299db9ec823\proptest-1.2.0\src\test_runner\runner.rs:574
  44:     0x7ff65259fce1 - proptest::test_runner::runner::TestRunner::run<proptest::strategy::map::Map<proptest::strategy::map::Map<proptest::collection::VecStrategy<proptest::strategy::unions::TupleUnion<tuple$<tuple$<u32,alloc::sync::Arc<proptest::strategy::map::Map<proptest::str
                               at C:\Users\Chase\.cargo\registry\src\github.heygears.com-1ecc6299db9ec823\proptest-1.2.0\src\test_runner\runner.rs:417
  45:     0x7ff6522b0ffc - dataflow_jit::codegen::vtable::tests::proptests::vtables
                               at C:\Users\Chase\.cargo\registry\src\github.heygears.com-1ecc6299db9ec823\proptest-1.2.0\src\sugar.rs:163
  46:     0x7ff651edc0e8 - dataflow_jit::codegen::vtable::tests::proptests::vtables::closure$0
                               at C:\Users\Chase\.cargo\registry\src\github.heygears.com-1ecc6299db9ec823\proptest-1.2.0\src\sugar.rs:159
  47:     0x7ff651cd0582 - core::ops::function::FnOnce::call_once<dataflow_jit::codegen::vtable::tests::proptests::vtables::closure_env$0,tuple$<> >
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483\library\core\src\ops\function.rs:507
  48:     0x7ff6528d162f - core::ops::function::FnOnce::call_once
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\core\src\ops\function.rs:507
  49:     0x7ff6528d162f - test::__rust_begin_short_backtrace<enum2$<core::result::Result<tuple$<>,alloc::string::String> >,enum2$<core::result::Result<tuple$<>,alloc::string::String> > (*)()>
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\test\src\lib.rs:657
  50:     0x7ff652899730 - test::run_test::closure$1
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\test\src\lib.rs:648
  51:     0x7ff652899730 - core::ops::function::FnOnce::call_once<test::run_test::closure_env$1,tuple$<> >
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\core\src\ops\function.rs:507
  52:     0x7ff6528cfe8d - alloc::boxed::impl$45::call_once
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\alloc\src\boxed.rs:2000
  53:     0x7ff6528cfe8d - core::panic::unwind_safe::impl$23::call_once
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\core\src\panic\unwind_safe.rs:271
  54:     0x7ff6528cfe8d - std::panicking::try::do_call
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\panicking.rs:483
  55:     0x7ff6528cfe8d - std::panicking::try
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\panicking.rs:447
  56:     0x7ff6528cfe8d - std::panic::catch_unwind
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\panic.rs:137
  57:     0x7ff6528cfe8d - test::run_test_in_process
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\test\src\lib.rs:680
  58:     0x7ff6528cfe8d - test::run_test::run_test_inner::closure$0
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\test\src\lib.rs:574
  59:     0x7ff652890a0a - test::run_test::run_test_inner::closure$1
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\test\src\lib.rs:601
  60:     0x7ff652890a0a - std::sys_common::backtrace::__rust_begin_short_backtrace<test::run_test::run_test_inner::closure_env$1,tuple$<> >
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\sys_common\backtrace.rs:121
  61:     0x7ff652899a0b - std::thread::impl$0::spawn_unchecked_::closure$1::closure$0
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\thread\mod.rs:550
  62:     0x7ff652899a0b - core::panic::unwind_safe::impl$23::call_once
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\core\src\panic\unwind_safe.rs:271
  63:     0x7ff652899a0b - std::panicking::try::do_call
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\panicking.rs:483
  64:     0x7ff652899a0b - std::panicking::try
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\panicking.rs:447
  65:     0x7ff652899a0b - std::panic::catch_unwind
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\panic.rs:137
  66:     0x7ff652899a0b - std::thread::impl$0::spawn_unchecked_::closure$1
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\thread\mod.rs:549
  67:     0x7ff652899a0b - core::ops::function::FnOnce::call_once<std::thread::impl$0::spawn_unchecked_::closure_env$1<test::run_test::run_test_inner::closure_env$1,tuple$<> >,tuple$<> >
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\core\src\ops\function.rs:507
  68:     0x7ff6532b966c - alloc::boxed::impl$45::call_once
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\alloc\src\boxed.rs:2000
  69:     0x7ff6532b966c - alloc::boxed::impl$45::call_once
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\alloc\src\boxed.rs:2000
  70:     0x7ff6532b966c - std::sys::windows::thread::impl$0::new::thread_start
                               at /rustc/d5a82bbd26e1ad8b7401f6a718a9c57c96905483/library\std\src\sys\windows\thread.rs:56
  71:     0x7ffdcdfd7614 - BaseThreadInitThunk
  72:     0x7ffdce8626f1 - RtlUserThreadStart

So I'm not really sure how to deal with that

[jameysharp]

Yeah, 128-bit constants are currently awkward in Cranelift. Usually we build them out of smaller constants. If the value fits within a 64-bit constant then you can use iconst.i64 followed by uextend (or sextend if you want to sign-extend). Otherwise you can build the two 64-bit halves with iconst.i64 and then combine them with iconcat. There are examples in cranelift/filetests/filetests/runtests/i128-*.clif.

[afonso360]

Hey,

The best way to do that operation currently is to either use a iconcat to merge two iconst.i64's, or use sextend/uextend if your constant can fit in a i64.

See also isplit if you end up needing to separate it out again for whatever reason.

Bitcasting a 128bit vector into a i128 should work, but in practice it's not implemented in any backend (CC: #6104)

Edit: Oops, looks like @jameysharp beat me to it 😄

[jameysharp]

Hopefully this was all you needed, so I'm going to close this issue. But please re-open it if we missed something!

Ideally we'd either have better documentation explaining this, or we'd remove the weird special case around i128 constants. If anyone runs into this problem, finds this discussion, and wants to try to tackle either of those solutions, let's chat! Otherwise I don't know when either alternative will happen 😅