Try to deduplicate layout_of query work

Author: oli-obk

compiler/rustc_ty_utils/src/layout.rs

@@ -4,6 +4,7 @@ use rustc_index::bit_set::BitSet;
 use rustc_index::{IndexSlice, IndexVec};
 use rustc_middle::mir::{GeneratorLayout, GeneratorSavedLocal};
 use rustc_middle::query::Providers;
+use rustc_middle::traits::Reveal;
 use rustc_middle::ty::layout::{
     IntegerExt, LayoutCx, LayoutError, LayoutOf, TyAndLayout, MAX_SIMD_LANES,
 };
@@ -51,7 +52,19 @@ fn layout_of<'tcx>(
         }
     };
 
-    if ty != unnormalized_ty {
+    if ty == unnormalized_ty {
+        // see comment in eval_to_allocation_raw_provider for what we're doing here
+        if param_env.reveal() == Reveal::All {
+            let mut query = query;
+            query.param_env = param_env.with_user_facing();
+            match tcx.layout_of(query) {
+                // try again with reveal all as requested
+                Err(LayoutError::Unknown(_) | LayoutError::NormalizationFailure(_, _)) => {}
+                // deduplicate calls
+                other => return other,
+            }
+        }
+    } else {
         // Ensure this layout is also cached for the normalized type.
         return tcx.layout_of(param_env.and(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