Rollup merge of #117385 - RalfJung:deduce_param_attrs, r=oli-obk

fmease · web-flow · commit 288ab168952f · 2023-10-30T10:48:21.000+01:00
deduce_param_attrs: explain a read-only case This takes the discussion [here](https://github.com/rust-lang/rust/pull/111517/files#r1243443625) and adds it as comment in the code. Cc `@lukas-code`
diff --git a/compiler/rustc_mir_transform/src/deduce_param_attrs.rs b/compiler/rustc_mir_transform/src/deduce_param_attrs.rs
@@ -44,6 +44,7 @@ impl<'tcx> Visitor<'tcx> for DeduceReadOnly {
                 // Whether mutating though a `&raw const` is allowed is still undecided, so we
                 // disable any sketchy `readonly` optimizations for now.
                 // But we only need to do this if the pointer would point into the argument.
+                // IOW: for indirect places, like `&raw (*local).field`, this surely cannot mutate `local`.
                 !place.is_indirect()
             }
             PlaceContext::NonMutatingUse(..) | PlaceContext::NonUse(..) => {

Original file line number	Diff line number	Diff line change
`@@ -44,6 +44,7 @@ impl<'tcx> Visitor<'tcx> for DeduceReadOnly {`
`44`	`44`	// Whether mutating though a `&raw const` is allowed is still undecided, so we
`45`	`45`	// disable any sketchy `readonly` optimizations for now.
`46`	`46`	`// But we only need to do this if the pointer would point into the argument.`
	`47`	+ // IOW: for indirect places, like `&raw (*local).field`, this surely cannot mutate `local`.
`47`	`48`	`!place.is_indirect()`
`48`	`49`	`}`
`49`	`50`	`PlaceContext::NonMutatingUse(..) \| PlaceContext::NonUse(..) => {`