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Move return_at_end out of Settings and into the wasm FuncEnvironment. (#547)

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* Move `return_at_end` out of Settings and into the wasm FuncEnvironment.

The `return_at_end` flag supports users that want to append a custom
epilogue to Cranelift-produced functions. It arranges for functions to
always return via a single return statement at the end, and users are
expected to remove this return to append their code.

This patch makes two changes:
 - First, introduce a `fallthrough_return` instruction and use that
   instead of adding a `return` at the end. That's simpler than having
   users remove the `return` themselves.

 - Second, move this setting out of the Settings and into the wasm
   FuncEnvironment. This flag isn't something the code generator uses,
   it's something that the wasm translator uses. The code generator
   needs to preserve the property, however we can give the
   `fallthrough_return` instruction properties to ensure this as needed,
   such as marking it non-cloneable.
This commit is contained in:
Dan Gohman
2018-10-05 06:43:22 -07:00
committed by GitHub
parent c61722f83f
commit bf041e3ae2
14 changed files with 91 additions and 91 deletions
Download Patch File Download Diff File Expand all files Collapse all files

22
cranelift/filetests/verifier/return_at_end.clif
View File

@@ -1,22 +0,0 @@
test verifier
set return_at_end
function %ok(i32) {
ebb0(v0: i32):
brnz v0, ebb1
trap int_divz
ebb1:
trapz v0, user5
return
}
function %bad(i32) {
ebb0(v0: i32):
brnz v0, ebb1
return ; error: Internal return not allowed
ebb1:
trapz v0, user6
return
}

11
cranelift/src/wasm.rs
View File

@@ -11,7 +11,9 @@ use cranelift_codegen::print_errors::{pretty_error, pretty_verifier_error};
use cranelift_codegen::settings::FlagsOrIsa;
use cranelift_codegen::Context;
use cranelift_entity::EntityRef;
use cranelift_wasm::{translate_module, DummyEnvironment, FuncIndex, ModuleEnvironment};
use cranelift_wasm::{
translate_module, DummyEnvironment, FuncIndex, ModuleEnvironment, ReturnMode,
};
use std::error::Error;
use std::path::Path;
use std::path::PathBuf;
@@ -102,8 +104,11 @@ fn handle_module(
}
};
let mut dummy_environ =
DummyEnvironment::with_triple_flags(isa.triple().clone(), fisa.flags.clone());
let mut dummy_environ = DummyEnvironment::with_triple_flags(
isa.triple().clone(),
fisa.flags.clone(),
ReturnMode::NormalReturns,
);
translate_module(&module_binary, &mut dummy_environ).map_err(|e| e.to_string())?;
let _ = terminal.fg(term::color::GREEN);

0
cranelift/wasmtests/return_at_end.wat → cranelift/wasmtests/use_fallthrough_return.wat
View File

10
lib/codegen/meta-python/base/instructions.py
View File

@@ -234,6 +234,16 @@ x_return = Instruction(
""",
ins=rvals, is_return=True, is_terminator=True)
fallthrough_return = Instruction(
'fallthrough_return', r"""
Return from the function by fallthrough.
This is a specialized instruction for use where one wants to append
a custom epilogue, which will then perform the real return. This
instruction has no encoding.
""",
ins=rvals, is_return=True, is_terminator=True)
FN = Operand(
'FN',
entities.func_ref,

10
lib/codegen/meta-python/base/settings.py
View File

@@ -65,16 +65,6 @@ colocated_libcalls = BoolSetting(
they can use more efficient addressing.
""")
return_at_end = BoolSetting(
"""
Generate functions with at most a single return instruction at the
end of the function.
This guarantees that functions do not have any internal return
instructions. Either they never return, or they have a single return
instruction at the end.
""")
avoid_div_traps = BoolSetting(
"""
Generate explicit checks around native division instructions to avoid

1
lib/codegen/src/settings.rs
View File

@@ -370,7 +370,6 @@ mod tests {
call_conv = \"fast\"\n\
is_pic = false\n\
colocated_libcalls = false\n\
return_at_end = false\n\
avoid_div_traps = false\n\
enable_float = true\n\
enable_nan_canonicalization = false\n\

30
lib/codegen/src/verifier/mod.rs
View File

@@ -307,7 +307,6 @@ struct Verifier<'a> {
func: &'a Function,
expected_cfg: ControlFlowGraph,
expected_domtree: DominatorTree,
flags: &'a Flags,
isa: Option<&'a TargetIsa>,
}
@@ -319,7 +318,6 @@ impl<'a> Verifier<'a> {
func,
expected_cfg,
expected_domtree,
flags: fisa.flags,
isa: fisa.isa,
}
}
@@ -1654,9 +1652,9 @@ impl<'a> Verifier<'a> {
// Instructions with side effects are not allowed to be ghost instructions.
let opcode = self.func.dfg[inst].opcode();
// The `fallthrough` instruction is marked as a terminator and a branch, but it is not
// required to have an encoding.
if opcode == Opcode::Fallthrough {
// The `fallthrough` and `fallthrough_return` instructions are marked as terminators and
// branches, but they are not required to have an encoding.
if opcode == Opcode::Fallthrough || opcode == Opcode::FallthroughReturn {
return Ok(());
}
@@ -1696,24 +1694,6 @@ impl<'a> Verifier<'a> {
Ok(())
}
/// Verify the `return_at_end` property which requires that there are no internal return
/// instructions.
fn verify_return_at_end(&self, errors: &mut VerifierErrors) -> VerifierStepResult<()> {
for ebb in self.func.layout.ebbs() {
let inst = self.func.layout.last_inst(ebb).unwrap();
if self.func.dfg[inst].opcode().is_return() && Some(ebb) != self.func.layout.last_ebb()
{
report!(
errors,
inst,
"Internal return not allowed with return_at_end=1"
);
}
}
errors.as_result()
}
pub fn run(&self, errors: &mut VerifierErrors) -> VerifierStepResult<()> {
self.verify_global_values(errors)?;
self.verify_heaps(errors)?;
@@ -1729,10 +1709,6 @@ impl<'a> Verifier<'a> {
}
}
if self.flags.return_at_end() {
self.verify_return_at_end(errors)?;
}
verify_flags(self.func, &self.expected_cfg, self.isa, errors)?;
Ok(())

11
lib/wasm/src/code_translator.rs
View File

@@ -28,7 +28,7 @@ use cranelift_codegen::ir::{self, InstBuilder, JumpTableData, MemFlags};
use cranelift_codegen::packed_option::ReservedValue;
use cranelift_entity::EntityRef;
use cranelift_frontend::{FunctionBuilder, Variable};
use environ::{FuncEnvironment, GlobalVariable, WasmError, WasmResult};
use environ::{FuncEnvironment, GlobalVariable, ReturnMode, WasmError, WasmResult};
use state::{ControlStackFrame, TranslationState};
use std::collections::{hash_map, HashMap};
use std::vec::Vec;
@@ -340,11 +340,10 @@ pub fn translate_operator<FE: FuncEnvironment + ?Sized>(
};
{
let args = state.peekn(return_count);
if environ.flags().return_at_end() {
builder.ins().jump(br_destination, args);
} else {
builder.ins().return_(args);
}
match environ.return_mode() {
ReturnMode::NormalReturns => builder.ins().return_(args),
ReturnMode::FallthroughReturn => builder.ins().jump(br_destination, args),
};
}
state.popn(return_count);
state.reachable = false;

37
lib/wasm/src/environ/dummy.rs
View File

@@ -7,7 +7,7 @@ use cranelift_codegen::ir::types::*;
use cranelift_codegen::ir::{self, InstBuilder};
use cranelift_codegen::settings;
use cranelift_entity::{EntityRef, PrimaryMap};
use environ::{FuncEnvironment, GlobalVariable, ModuleEnvironment, WasmResult};
use environ::{FuncEnvironment, GlobalVariable, ModuleEnvironment, ReturnMode, WasmResult};
use func_translator::FuncTranslator;
use std::string::String;
use std::vec::Vec;
@@ -105,38 +105,55 @@ pub struct DummyEnvironment {
/// Vector of wasm bytecode size for each function.
pub func_bytecode_sizes: Vec<usize>,
/// How to return from functions.
return_mode: ReturnMode,
}
impl DummyEnvironment {
/// Allocates the data structures with default flags.
pub fn with_triple(triple: Triple) -> Self {
Self::with_triple_flags(triple, settings::Flags::new(settings::builder()))
Self::with_triple_flags(
triple,
settings::Flags::new(settings::builder()),
ReturnMode::NormalReturns,
)
}
/// Allocates the data structures with the given flags.
pub fn with_triple_flags(triple: Triple, flags: settings::Flags) -> Self {
/// Allocates the data structures with the given triple.
pub fn with_triple_flags(
triple: Triple,
flags: settings::Flags,
return_mode: ReturnMode,
) -> Self {
Self {
info: DummyModuleInfo::with_triple_flags(triple, flags),
trans: FuncTranslator::new(),
func_bytecode_sizes: Vec::new(),
return_mode,
}
}
/// Return a `DummyFuncEnvironment` for translating functions within this
/// `DummyEnvironment`.
pub fn func_env(&self) -> DummyFuncEnvironment {
DummyFuncEnvironment::new(&self.info)
DummyFuncEnvironment::new(&self.info, self.return_mode)
}
}
/// The `FuncEnvironment` implementation for use by the `DummyEnvironment`.
pub struct DummyFuncEnvironment<'dummy_environment> {
pub mod_info: &'dummy_environment DummyModuleInfo,
return_mode: ReturnMode,
}
impl<'dummy_environment> DummyFuncEnvironment<'dummy_environment> {
pub fn new(mod_info: &'dummy_environment DummyModuleInfo) -> Self {
Self { mod_info }
pub fn new(mod_info: &'dummy_environment DummyModuleInfo, return_mode: ReturnMode) -> Self {
Self {
mod_info,
return_mode,
}
}
// Create a signature for `sigidx` amended with a `vmctx` argument after the standard wasm
@@ -321,6 +338,10 @@ impl<'dummy_environment> FuncEnvironment for DummyFuncEnvironment<'dummy_environ
) -> WasmResult<ir::Value> {
Ok(pos.ins().iconst(I32, -1))
}
fn return_mode(&self) -> ReturnMode {
self.return_mode
}
}
impl<'data> ModuleEnvironment<'data> for DummyEnvironment {
@@ -433,7 +454,7 @@ impl<'data> ModuleEnvironment<'data> for DummyEnvironment {
fn define_function_body(&mut self, body_bytes: &'data [u8]) -> WasmResult<()> {
let func = {
let mut func_environ = DummyFuncEnvironment::new(&self.info);
let mut func_environ = DummyFuncEnvironment::new(&self.info, self.return_mode);
let func_index =
FuncIndex::new(self.get_num_func_imports() + self.info.function_bodies.len());
let name = get_func_name(func_index);

2
lib/wasm/src/environ/mod.rs
View File

@@ -5,5 +5,5 @@ mod spec;
pub use environ::dummy::DummyEnvironment;
pub use environ::spec::{
FuncEnvironment, GlobalVariable, ModuleEnvironment, WasmError, WasmResult,
FuncEnvironment, GlobalVariable, ModuleEnvironment, ReturnMode, WasmError, WasmResult,
};

14
lib/wasm/src/environ/spec.rs
View File

@@ -74,6 +74,15 @@ impl WasmError {
/// A convenient alias for a `Result` that uses `WasmError` as the error type.
pub type WasmResult<T> = Result<T, WasmError>;
/// How to return from functions.
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub enum ReturnMode {
/// Use normal return instructions as needed.
NormalReturns,
/// Use a single fallthrough return at the end of the function.
FallthroughReturn,
}
/// Environment affecting the translation of a single WebAssembly function.
///
/// A `FuncEnvironment` trait object is required to translate a WebAssembly function to Cranelift
@@ -216,6 +225,11 @@ pub trait FuncEnvironment {
fn translate_loop_header(&mut self, _pos: FuncCursor) {
// By default, don't emit anything.
}
/// Should the code be structured to use a single `fallthrough_return` instruction at the end
/// of the function body, rather than `return` instructions as needed? This is used by VMs
/// to append custom epilogues.
fn return_mode(&self) -> ReturnMode;
}
/// An object satisfying the `ModuleEnvironment` trait can be passed as argument to the

7
lib/wasm/src/func_translator.rs
View File

@@ -9,7 +9,7 @@ use cranelift_codegen::entity::EntityRef;
use cranelift_codegen::ir::{self, Ebb, InstBuilder};
use cranelift_codegen::timing;
use cranelift_frontend::{FunctionBuilder, FunctionBuilderContext, Variable};
use environ::{FuncEnvironment, WasmError, WasmResult};
use environ::{FuncEnvironment, ReturnMode, WasmError, WasmResult};
use state::TranslationState;
use wasmparser::{self, BinaryReader};
@@ -209,7 +209,10 @@ fn parse_function_body<FE: FuncEnvironment + ?Sized>(
if state.reachable {
debug_assert!(builder.is_pristine());
if !builder.is_unreachable() {
builder.ins().return_(&state.stack);
match environ.return_mode() {
ReturnMode::NormalReturns => builder.ins().return_(&state.stack),
ReturnMode::FallthroughReturn => builder.ins().fallthrough_return(&state.stack),
};
}
}

3
lib/wasm/src/lib.rs
View File

@@ -59,7 +59,8 @@ mod state;
mod translation_utils;
pub use environ::{
DummyEnvironment, FuncEnvironment, GlobalVariable, ModuleEnvironment, WasmError, WasmResult,
DummyEnvironment, FuncEnvironment, GlobalVariable, ModuleEnvironment, ReturnMode, WasmError,
WasmResult,
};
pub use func_translator::FuncTranslator;
pub use module_translator::translate_module;

24
lib/wasm/tests/wasm_testsuite.rs
View File

@@ -6,9 +6,9 @@ extern crate wabt;
use cranelift_codegen::isa;
use cranelift_codegen::print_errors::pretty_verifier_error;
use cranelift_codegen::settings::{self, Configurable, Flags};
use cranelift_codegen::settings::{self, Flags};
use cranelift_codegen::verifier;
use cranelift_wasm::{translate_module, DummyEnvironment};
use cranelift_wasm::{translate_module, DummyEnvironment, ReturnMode};
use std::fs;
use std::fs::File;
use std::io;
@@ -35,16 +35,18 @@ fn testsuite() {
let flags = Flags::new(settings::builder());
for path in paths {
let path = path.path();
handle_module(&path, &flags);
handle_module(&path, &flags, ReturnMode::NormalReturns);
}
}
#[test]
fn return_at_end() {
let mut flag_builder = settings::builder();
flag_builder.enable("return_at_end").unwrap();
let flags = Flags::new(flag_builder);
handle_module(Path::new("../../wasmtests/return_at_end.wat"), &flags);
fn use_fallthrough_return() {
let flags = Flags::new(settings::builder());
handle_module(
Path::new("../../wasmtests/use_fallthrough_return.wat"),
&flags,
ReturnMode::FallthroughReturn,
);
}
fn read_file(path: &Path) -> io::Result<Vec<u8>> {
@@ -54,7 +56,7 @@ fn read_file(path: &Path) -> io::Result<Vec<u8>> {
Ok(buf)
}
fn handle_module(path: &Path, flags: &Flags) {
fn handle_module(path: &Path, flags: &Flags, return_mode: ReturnMode) {
let data = match path.extension() {
None => {
panic!("the file extension is not wasm or wat");
@@ -73,7 +75,9 @@ fn handle_module(path: &Path, flags: &Flags) {
None | Some(&_) => panic!("the file extension for {:?} is not wasm or wat", path),
},
};
let mut dummy_environ = DummyEnvironment::with_triple_flags(triple!("riscv64"), flags.clone());
let mut dummy_environ =
DummyEnvironment::with_triple_flags(triple!("riscv64"), flags.clone(), return_mode);
translate_module(&data, &mut dummy_environ).unwrap();
let isa = isa::lookup(dummy_environ.info.triple)