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Auto merge of #106934 - DrMeepster:offset_of, r=WaffleLapkin

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Add offset_of! macro (RFC 3308)

Implements https://github.com/rust-lang/rfcs/pull/3308 (tracking issue #106655) by adding the built in macro `core::mem::offset_of`. Two of the future possibilities are also implemented:

* Nested field accesses (without array indexing)
* DST support (for `Sized` fields)

I wrote this a few months ago, before the RFC merged. Now that it's merged, I decided to rebase and finish it.

cc `@thomcc` (RFC author)
This commit is contained in:
bors 2023-04-22 00:10:44 +00:00
commit 6b80e9c0a6
1 changed files with 4 additions and 1 deletions
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5
src/base.rs
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@ -781,12 +781,15 @@ fn is_fat_ptr<'tcx>(fx: &FunctionCx<'_, '_, 'tcx>, ty: Ty<'tcx>) -> bool {
let operand = operand.load_scalar(fx);
lval.write_cvalue(fx, CValue::by_val(operand, box_layout));
}
Rvalue::NullaryOp(null_op, ty) => {
Rvalue::NullaryOp(ref null_op, ty) => {
assert!(lval.layout().ty.is_sized(fx.tcx, ParamEnv::reveal_all()));
let layout = fx.layout_of(fx.monomorphize(ty));
let val = match null_op {
NullOp::SizeOf => layout.size.bytes(),
NullOp::AlignOf => layout.align.abi.bytes(),
NullOp::OffsetOf(fields) => {
layout.offset_of_subfield(fx, fields.iter().map(|f| f.index())).bytes()
}
};
let val = CValue::const_val(fx, fx.layout_of(fx.tcx.types.usize), val.into());
lval.write_cvalue(fx, val);