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Fetch the value of has_ffi_unwind_calls before stealing mir_built. #108777

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Fetch the value of has_ffi_unwind_calls before stealing mir_built. #108777

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5 changes: 2 additions & 3 deletions compiler/rustc_mir_transform/src/ffi_unwind_calls.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -47,14 +47,12 @@ fn has_ffi_unwind_calls(tcx: TyCtxt<'_>, local_def_id: LocalDefId) -> bool {
return false;
}

let body = &*tcx.mir_built(ty::WithOptConstParam::unknown(local_def_id)).borrow();

let body_ty = tcx.type_of(def_id).skip_binder();
let body_abi = match body_ty.kind() {
ty::FnDef(..) => body_ty.fn_sig(tcx).abi(),
ty::Closure(..) => Abi::RustCall,
ty::Generator(..) => Abi::Rust,
_ => span_bug!(body.span, "unexpected body ty: {:?}", body_ty),
_ => span_bug!(tcx.def_span(def_id), "unexpected body ty: {:?}", body_ty),
};
let body_can_unwind = layout::fn_can_unwind(tcx, Some(def_id), body_abi);

Expand All @@ -65,6 +63,7 @@ fn has_ffi_unwind_calls(tcx: TyCtxt<'_>, local_def_id: LocalDefId) -> bool {

let mut tainted = false;

let body = &*tcx.mir_built(ty::WithOptConstParam::unknown(local_def_id)).borrow();
for block in body.basic_blocks.iter() {
if block.is_cleanup {
continue;
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8 changes: 6 additions & 2 deletions compiler/rustc_mir_transform/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -284,8 +284,12 @@ fn mir_const(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> &Steal<
}
}

// has_ffi_unwind_calls query uses the raw mir, so make sure it is run.
tcx.ensure().has_ffi_unwind_calls(def.did);
// has_ffi_unwind_calls query uses `mir_built(WithOptConstParam::unknown(def.did))`,
// so make sure it is run.
if def.const_param_did.is_none() {
// Actually fetch the value, to avoid having to compute the query later.
let _ = tcx.has_ffi_unwind_calls(def.did);
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There are ensure() calls few lines above this, are they unaffected by the same issue for some reason?

Also, what is the use-case for ensure, if it doesn't ensure that we have the query value?... I'm very confused by all of this...

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ensure creates a dependency edge. However, it does not compute the value. For instance, if has_ffi_unwind_calls were to emit diagnostics, ensure would check that the dependencies are unchanged, replay the diagnostics (loaded from disk), but wouldn't try to load the cached value.

And yes, all uses of ensure() before a steal() are probably wrong. However, I find unelegant to invoke a query just to ignore its result.

There are 2 ways to definitely fix this:

  1. change most of the ensures;
  2. check that we can decode the value from disk on ensure.

I'm leaning on 2, but haven't finished implementing it.

}

let mut body = tcx.mir_built(def).steal();

Expand Down