skip const-eval if evaluatable predicate is trivial

Author: dingxiangfei2009

compiler/rustc_trait_selection/src/traits/const_evaluatable.rs

@@ -37,13 +37,17 @@ pub fn is_const_evaluatable<'tcx>(
         | ty::ConstKind::Value(_, _)
         | ty::ConstKind::Error(_) => return Ok(()),
         ty::ConstKind::Infer(_) => return Err(NotConstEvaluatable::MentionsInfer),
-    };
+    }
 
     if tcx.features().generic_const_exprs {
         let ct = tcx.expand_abstract_consts(unexpanded_ct);
 
+        if trivially_satisfied_from_param_env(ct, param_env) {
+            return Ok(());
+        }
+
         let is_anon_ct = if let ty::ConstKind::Unevaluated(uv) = ct.kind() {
-            tcx.def_kind(uv.def) == DefKind::AnonConst
+            matches!(tcx.def_kind(uv.def), DefKind::AnonConst)
         } else {
             false
         };
@@ -150,6 +154,23 @@ pub fn is_const_evaluatable<'tcx>(
     }
 }
 
+fn trivially_satisfied_from_param_env<'tcx>(
+    ct: ty::Const<'tcx>,
+    param_env: ty::ParamEnv<'tcx>,
+) -> bool {
+    for pred in param_env.caller_bounds() {
+        if let ty::ClauseKind::ConstEvaluatable(ce) = pred.kind().skip_binder() {
+            if let ty::ConstKind::Unevaluated(uv_env) = ce.kind()
+                && let ty::ConstKind::Unevaluated(uv) = ct.kind()
+                && uv == uv_env
+            {
+                return true;
+            }
+        }
+    }
+    false
+}
+
 #[instrument(skip(infcx, tcx), level = "debug")]
 fn satisfied_from_param_env<'tcx>(
     tcx: TyCtxt<'tcx>,

tests/crashes/123959.rs renamed to tests/ui/const-generics/generic_const_exprs/ice-123959.rs

@@ -1,5 +1,7 @@
-//@ known-bug: #123959
+//@ check-pass
 #![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
+
 fn foo<T>(_: [(); std::mem::offset_of!((T,), 0)]) {}
 
 pub fn main() {}

tests/ui/const-generics/generic_const_exprs/unevaluated-const-ice-119731.rs

@@ -14,8 +14,8 @@ mod v20 {
     //~^ ERROR cannot find value `v8` in this scope
     //~| ERROR cannot find function `v6` in this scope
     pub struct v17<const v10: usize, const v7: v11> {
-    //~^ WARN type `v17` should have an upper camel case name
-    //~| ERROR `[[usize; v4]; v4]` is forbidden as the type of a const generic parameter
+        //~^ WARN type `v17` should have an upper camel case name
+        //~| ERROR `[[usize; v4]; v4]` is forbidden as the type of a const generic parameter
         _p: (),
     }
 
@@ -25,10 +25,9 @@ mod v20 {
     }
 
     impl<const v10: usize> v17<v10, v2> {
-    //~^ ERROR maximum number of nodes exceeded in constant v20::v17::<v10, v2>::{constant#1}
-    //~| ERROR maximum number of nodes exceeded in constant v20::v17::<v10, v2>::{constant#1}
+        //~^ ERROR maximum number of nodes exceeded in constant v20::v17::<v10, v2>::{constant#1}
         pub const fn v21() -> v18 {
-        //~^ ERROR cannot find type `v18` in this scope
+            //~^ ERROR cannot find type `v18` in this scope
             v18 { _p: () }
             //~^ ERROR cannot find struct, variant or union type `v18` in this scope
         }

tests/ui/const-generics/generic_const_exprs/unevaluated-const-ice-119731.stderr

@@ -1,5 +1,5 @@
 error[E0432]: unresolved import `v20::v13`
-  --> $DIR/unevaluated-const-ice-119731.rs:37:15
+  --> $DIR/unevaluated-const-ice-119731.rs:36:15
    |
 LL | pub use v20::{v13, v17};
    |               ^^^
@@ -23,7 +23,7 @@ LL |         pub const fn v21() -> v18 {}
    |                               ^^^ help: a type alias with a similar name exists: `v11`
 
 error[E0412]: cannot find type `v18` in this scope
-  --> $DIR/unevaluated-const-ice-119731.rs:30:31
+  --> $DIR/unevaluated-const-ice-119731.rs:29:31
    |
 LL |     pub type v11 = [[usize; v4]; v4];
    |     --------------------------------- similarly named type alias `v11` defined here
@@ -32,7 +32,7 @@ LL |         pub const fn v21() -> v18 {
    |                               ^^^ help: a type alias with a similar name exists: `v11`
 
 error[E0422]: cannot find struct, variant or union type `v18` in this scope
-  --> $DIR/unevaluated-const-ice-119731.rs:32:13
+  --> $DIR/unevaluated-const-ice-119731.rs:31:13
    |
 LL |     pub type v11 = [[usize; v4]; v4];
    |     --------------------------------- similarly named type alias `v11` defined here
@@ -78,15 +78,7 @@ error: maximum number of nodes exceeded in constant v20::v17::<v10, v2>::{consta
 LL |     impl<const v10: usize> v17<v10, v2> {
    |                                     ^^
 
-error: maximum number of nodes exceeded in constant v20::v17::<v10, v2>::{constant#1}
-  --> $DIR/unevaluated-const-ice-119731.rs:27:37
-   |
-LL |     impl<const v10: usize> v17<v10, v2> {
-   |                                     ^^
-   |
-   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-
-error: aborting due to 9 previous errors; 2 warnings emitted
+error: aborting due to 8 previous errors; 2 warnings emitted
 
 Some errors have detailed explanations: E0412, E0422, E0425, E0432.
 For more information about an error, try `rustc --explain E0412`.