Reuse cached layout from PostAnalysis when possible.

Author: cjgillot

compiler/rustc_ty_utils/src/layout.rs

@@ -62,6 +62,18 @@ fn layout_of<'tcx>(
         return tcx.layout_of(typing_env.as_query_input(ty));
     }
 
+    if let ty::TypingMode::Codegen = typing_env.typing_mode {
+        let with_postanalysis = ty::TypingEnv {
+            typing_mode: ty::TypingMode::PostAnalysis,
+            param_env: typing_env.param_env,
+        };
+        let res = tcx.layout_of(with_postanalysis.as_query_input(ty));
+        match res {
+            Err(LayoutError::TooGeneric(_)) => {}
+            _ => return res,
+        };
+    }
+
     let cx = LayoutCx::new(tcx, typing_env);
 
     let layout = layout_of_uncached(&cx, ty)?;

tests/ui/layout/layout-cycle.stderr

@@ -2,6 +2,7 @@ error[E0391]: cycle detected when computing layout of `S<S<()>>`
    |
    = note: ...which requires computing layout of `<S<()> as Tr>::I`...
    = note: ...which again requires computing layout of `S<S<()>>`, completing the cycle
+   = note: cycle used when computing layout of `S<S<()>>`
    = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
 
 error: failed to get layout for S<S<()>>: a cycle occurred during layout computation

tests/ui/recursion_limit/zero-overflow.rs

@@ -1,4 +1,4 @@
-//~ ERROR overflow evaluating the requirement `&mut Self: DispatchFromDyn<&mut RustaceansAreAwesome>
+//~ ERROR queries overflow the depth limit!
 //~| HELP consider increasing the recursion limit
 //@ build-fail
 

tests/ui/recursion_limit/zero-overflow.stderr

@@ -1,7 +1,7 @@
-error[E0275]: overflow evaluating the requirement `&mut Self: DispatchFromDyn<&mut RustaceansAreAwesome>`
+error: queries overflow the depth limit!
    |
    = help: consider increasing the recursion limit by adding a `#![recursion_limit = "2"]` attribute to your crate (`zero_overflow`)
+   = note: query depth increased by 2 when computing layout of `isize`
 
 error: aborting due to 1 previous error
 
-For more information about this error, try `rustc --explain E0275`.

tests/ui/transmutability/structs/repr/transmute_infinitely_recursive_type.stderr

@@ -12,7 +12,7 @@ LL |     struct ExplicitlyPadded(Box<ExplicitlyPadded>);
 error[E0391]: cycle detected when computing layout of `should_pad_explicitly_packed_field::ExplicitlyPadded`
    |
    = note: ...which immediately requires computing layout of `should_pad_explicitly_packed_field::ExplicitlyPadded` again
-   = note: cycle used when evaluating trait selection obligation `(): core::mem::transmutability::TransmuteFrom<should_pad_explicitly_packed_field::ExplicitlyPadded, ValTree(Branch([Leaf(0x00), Leaf(0x00), Leaf(0x00), Leaf(0x00)]): core::mem::transmutability::Assume)>`
+   = note: cycle used when computing layout of `should_pad_explicitly_packed_field::ExplicitlyPadded`
    = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information
 
 error: aborting due to 2 previous errors