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Rollup merge of #115762 - oli-obk:early_const_prop_lint2, r=compiler-errors

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Explain revealing of opaque types in layout_of ParamEnv

r? `@compiler-errors`

~~I feel like `layout_of` is doing too many things at once, and I don't really know why. It could allow us to if callers could decide whether to reveal opaque types.~~

Looks like this also exists as a performance optimization. While we could probably figure out a way to do this, all the ones I came up with are fragile as `layout_of` callers now suddenly need to be careful what ParamEnv they pass in.
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Matthias Krüger 2023-09-18 18:27:20 +02:00 committed by GitHub
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compiler/rustc_ty_utils/src/layout.rs
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@ -36,6 +36,9 @@ fn layout_of<'tcx>(
let (param_env, ty) = query.into_parts();
debug!(?ty);
// Optimization: We convert to RevealAll and convert opaque types in the where bounds
// to their hidden types. This reduces overall uncached invocations of `layout_of` and
// is thus a small performance improvement.
let param_env = param_env.with_reveal_all_normalized(tcx);
let unnormalized_ty = ty;