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Fix ICE when using Box<T, A> with pointer sized A #94043

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Feb 18, 2022
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Fix ICE when using Box<T, A> with pointer sized A #94043

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ae32f43
fix assumption that ScalarPair Box is always a fat pointer
beepster4096 Feb 16, 2022
d0b508e
add comment explaining the check
beepster4096 Feb 17, 2022
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4 changes: 3 additions & 1 deletion compiler/rustc_codegen_llvm/src/type_of.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -330,7 +330,9 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyAndLayout<'tcx> {
ty::Ref(..) | ty::RawPtr(_) => {
return self.field(cx, index).llvm_type(cx);
}
ty::Adt(def, _) if def.is_box() => {
// only wide pointer boxes are handled as pointers
// thin pointer boxes with scalar allocators are handled by the general logic below
ty::Adt(def, substs) if def.is_box() && cx.layout_of(substs.type_at(1)).is_zst() => {
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Please leave a comment here stating that we only handle wide pointer boxes as pointers, not thin pointer boxes with a scalar allocator. That case is handled in the general logic below

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cc @antoyo I think cg_gcc needs the same fix.

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Seems like applying the same fix cause another issue.
Do you think there is the same issue for the LLVM codegen?
cc @drmeepster

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Looks like the problem is that in the mini_core test, Box doesn't have the allocator type parameter.

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Yeah, fixed it in cg_clif in bjorn3/rustc_codegen_cranelift@401b034. Feel free to copy the changes.

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Unfortunately, that doesn't solve the issue. I made changes more similar to liballoc itself, but got another ICE:

thread 'rustc' panicked at 'assertion failed: sig.c_variadic || extra_args.is_empty()', compiler/rustc_middle/src/ty/layout.rs:3027:13

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Did you change Box to include an extra field (eg ()) and change box_free to add an extra argument of the same type? They need to be in sync. I got the exact same error when I hadn't changed box_free yet.

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Yes.
What I meant is that I still get the error fixed by this PR with your changes:

thread 'rustc' panicked at 'index out of bounds: the len is 1 but the index is 1', /rustc/4b043faba34ccc053a4d0110634c323f6c03765e/compiler/rustc_middle/src/ty/subst.rs:364:43

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Oh, I see what you mean.
My own fixes miss the change you made to box_free.
Thanks. It works now!

let ptr_ty = cx.tcx.mk_mut_ptr(self.ty.boxed_ty());
return cx.layout_of(ptr_ty).scalar_pair_element_llvm_type(cx, index, immediate);
}
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6 changes: 6 additions & 0 deletions src/test/ui/box/issue-78459-ice.rs
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@@ -0,0 +1,6 @@
// check-pass
#![feature(allocator_api)]

fn main() {
Box::new_in((), &std::alloc::Global);
}