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x64 and aarch64: allow StructArgument and StructReturn args.

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The StructReturn ABI is fairly simple at the codegen/isel level: we only
need to take care to return the sret pointer as one of the return values
if that wasn't specified in the initial function signature.

Struct arguments are a little more complex. A struct argument is stored
as a chunk of memory in the stack-args space. However, the CLIF
semantics are slightly special: on the caller side, the parameter passed
in is a pointer to an arbitrary memory block, and we must memcpy this
data to the on-stack struct-argument; and on the callee side, we provide
a pointer to the passed-in struct-argument as the CLIF block param
value.

This is necessary to support various ABIs other than Wasm, such as that
of Rust (with the cg_clif codegen backend).
This commit is contained in:
Chris Fallin
2020-12-13 18:50:59 -08:00
parent 25088dee9d
commit 456561f431
14 changed files with 641 additions and 166 deletions
Download Patch File Download Diff File Expand all files Collapse all files

25
cranelift/codegen/src/machinst/lower.rs
View File

@@ -375,8 +375,9 @@ impl<'func, I: VCodeInst> Lower<'func, I> {
}
}
let vm_context = f
.signature
let vm_context = vcode
.abi()
.signature()
.special_param_index(ArgumentPurpose::VMContext)
.map(|vm_context_index| {
let entry_block = f.layout.entry_block().unwrap();
@@ -386,7 +387,7 @@ impl<'func, I: VCodeInst> Lower<'func, I> {
// Assign vreg(s) to each return value.
let mut retval_regs = vec![];
for ret in &f.signature.returns {
for ret in &vcode.abi().signature().returns.clone() {
let regs = alloc_vregs(ret.value_type, &mut next_vreg, &mut vcode)?;
retval_regs.push(regs);
debug!("retval gets regs {:?}", regs);
@@ -465,6 +466,24 @@ impl<'func, I: VCodeInst> Lower<'func, I> {
for insn in self.vcode.abi().gen_copy_arg_to_regs(i, regs).into_iter() {
self.emit(insn);
}
if self.abi().signature().params[i].purpose == ArgumentPurpose::StructReturn {
assert!(regs.len() == 1);
let ty = self.abi().signature().params[i].value_type;
// The ABI implementation must have ensured that a StructReturn
// arg is present in the return values.
let struct_ret_idx = self
.abi()
.signature()
.returns
.iter()
.position(|ret| ret.purpose == ArgumentPurpose::StructReturn)
.expect("StructReturn return value not present!");
self.emit(I::gen_move(
Writable::from_reg(self.retval_regs[struct_ret_idx].regs()[0]),
regs.regs()[0].to_reg(),
ty,
));
}
}
if let Some(insn) = self.vcode.abi().gen_retval_area_setup() {
self.emit(insn);