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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 80a2ec49a4
83 changed files with 1355 additions and 42 deletions
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5
compiler/rustc_codegen_ssa/src/mir/rvalue.rs
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@ -666,13 +666,16 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
}
}
mir::Rvalue::NullaryOp(null_op, ty) => {
mir::Rvalue::NullaryOp(ref null_op, ty) => {
let ty = self.monomorphize(ty);
assert!(bx.cx().type_is_sized(ty));
let layout = bx.cx().layout_of(ty);
let val = match null_op {
mir::NullOp::SizeOf => layout.size.bytes(),
mir::NullOp::AlignOf => layout.align.abi.bytes(),
mir::NullOp::OffsetOf(fields) => {
layout.offset_of_subfield(bx.cx(), fields.iter().map(|f| f.index())).bytes()
}
};
let val = bx.cx().const_usize(val);
let tcx = self.cx.tcx();