Reuse result from eval_to_const_value_raw.

Author: cjgillot

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -327,9 +327,40 @@ pub fn eval_to_const_value_raw_provider<'tcx>(
     tcx: TyCtxt<'tcx>,
     key: ty::PseudoCanonicalInput<'tcx, GlobalId<'tcx>>,
 ) -> ::rustc_middle::mir::interpret::EvalToConstValueResult<'tcx> {
-    if let Some((value, _ty)) = tcx.trivial_const(key.value.instance.def_id()) {
+    let ty::PseudoCanonicalInput { typing_env, value } = key;
+
+    if let Some((value, _ty)) = tcx.trivial_const(value.instance.def_id()) {
         return Ok(value);
     }
+
+    match typing_env.typing_mode().assert_not_erased() {
+        ty::TypingMode::PostAnalysis => {}
+        // We are in codegen. It's very likely this constant has been evaluated in PostAnalysis before.
+        // Try to reuse this evaluation, and only re-run if we hit a `TooGeneric` error.
+        ty::TypingMode::Codegen => {
+            let with_postanalysis =
+                ty::TypingEnv::new(typing_env.param_env, ty::TypingMode::PostAnalysis);
+            let with_postanalysis =
+                tcx.eval_to_const_value_raw(with_postanalysis.as_query_input(value));
+            match with_postanalysis {
+                Ok(_) | Err(ErrorHandled::Reported(..)) => return with_postanalysis,
+                Err(ErrorHandled::TooGeneric(_)) => {}
+            }
+        }
+        // Const eval always happens in PostAnalysis or Codegen mode. See the comment in
+        // `InterpCx::new` for more details.
+        ty::TypingMode::Coherence
+        | ty::TypingMode::Analysis { .. }
+        | ty::TypingMode::Borrowck { .. }
+        | ty::TypingMode::PostBorrowckAnalysis { .. } => {
+            if cfg!(debug_assertions) {
+                bug!(
+                    "Const eval should always happens in PostAnalysis or Codegen mode. See the comment in `InterpCx::new` for more details."
+                )
+            }
+        }
+    }
+
     tcx.eval_to_allocation_raw(key).map(|val| turn_into_const_value(tcx, val, key))
 }
 

tests/ui/associated-consts/issue-24949-assoc-const-static-recursion-trait.stderr

@@ -1,9 +1,14 @@
-error[E0391]: cycle detected when const-evaluating + checking `TRAIT_REF_BAR`
+error[E0391]: cycle detected when simplifying constant for the type system `TRAIT_REF_BAR`
+  --> $DIR/issue-24949-assoc-const-static-recursion-trait.rs:7:1
+   |
+LL | const TRAIT_REF_BAR: u32 = <GlobalTraitRef>::BAR;
+   | ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: ...which requires const-evaluating + checking `TRAIT_REF_BAR`...
   --> $DIR/issue-24949-assoc-const-static-recursion-trait.rs:7:28
    |
 LL | const TRAIT_REF_BAR: u32 = <GlobalTraitRef>::BAR;
    |                            ^^^^^^^^^^^^^^^^^^^^^
-   |
 note: ...which requires simplifying constant for the type system `<impl at $DIR/issue-24949-assoc-const-static-recursion-trait.rs:11:1: 11:28>::BAR`...
   --> $DIR/issue-24949-assoc-const-static-recursion-trait.rs:12:5
    |
@@ -24,13 +29,8 @@ note: ...which requires elaborating drops for `<impl at $DIR/issue-24949-assoc-c
    |
 LL |     const BAR: u32 = TRAIT_REF_BAR;
    |                      ^^^^^^^^^^^^^
-note: ...which requires simplifying constant for the type system `TRAIT_REF_BAR`...
-  --> $DIR/issue-24949-assoc-const-static-recursion-trait.rs:7:1
-   |
-LL | const TRAIT_REF_BAR: u32 = <GlobalTraitRef>::BAR;
-   | ^^^^^^^^^^^^^^^^^^^^^^^^
-   = note: ...which again requires const-evaluating + checking `TRAIT_REF_BAR`, completing the cycle
-note: cycle used when const-evaluating + checking `TRAIT_REF_BAR`
+   = note: ...which again requires simplifying constant for the type system `TRAIT_REF_BAR`, completing the cycle
+note: cycle used when simplifying constant for the type system `TRAIT_REF_BAR`
   --> $DIR/issue-24949-assoc-const-static-recursion-trait.rs:7:1
    |
 LL | const TRAIT_REF_BAR: u32 = <GlobalTraitRef>::BAR;

tests/ui/consts/const-eval/const-eval-query-stack.stderr

@@ -9,7 +9,7 @@ note: please make sure that you have updated to the latest nightly
 
 query stack during panic:
 #0 [eval_to_allocation_raw] const-evaluating + checking `X`
-#1 [eval_to_allocation_raw] const-evaluating + checking `X`
+#1 [eval_to_const_value_raw] simplifying constant for the type system `X`
 #2 [eval_to_const_value_raw] simplifying constant for the type system `X`
 #3 [analysis] running analysis passes on crate `const_eval_query_stack`
 end of query stack

tests/ui/consts/recursive-block.stderr

@@ -5,7 +5,7 @@ LL |     const { foo::<&T>() }
    |           ^^^^^^^^^^^^^^^
    |
    = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`recursive_block`)
-   = note: query depth increased by 1 when computing layout of `foo<&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&i32>`
+   = note: query depth increased by 1 when computing layout of `foo<&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&i32>`
 
 error: aborting due to 1 previous error