Auto merge of rust-lang#74949 - oli-obk:validate_const_eval_raw, r=RalfJung

Validate constants during `const_eval_raw`

This PR implements the groundwork for rust-lang#72396

* constants are now validated during `const_eval_raw`
* to prevent cycle errors, we do not validate references to statics anymore beyond the fact that they are not dangling
* the `const_eval` query ICEs if used on `static` items
* as a side effect promoteds are now evaluated to `ConstValue::Scalar` again (since they are just a reference to the actual promoted allocation in most cases).

Author: bors

compiler/rustc_codegen_llvm/src/consts.rs

@@ -12,7 +12,7 @@ use rustc_hir::def_id::DefId;
 use rustc_hir::Node;
 use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
 use rustc_middle::mir::interpret::{
-    read_target_uint, Allocation, ConstValue, ErrorHandled, GlobalAlloc, Pointer,
+    read_target_uint, Allocation, ErrorHandled, GlobalAlloc, Pointer,
 };
 use rustc_middle::mir::mono::MonoItem;
 use rustc_middle::ty::{self, Instance, Ty};
@@ -85,10 +85,7 @@ pub fn codegen_static_initializer(
     cx: &CodegenCx<'ll, 'tcx>,
     def_id: DefId,
 ) -> Result<(&'ll Value, &'tcx Allocation), ErrorHandled> {
-    let alloc = match cx.tcx.const_eval_poly(def_id)? {
-        ConstValue::ByRef { alloc, offset } if offset.bytes() == 0 => alloc,
-        val => bug!("static const eval returned {:#?}", val),
-    };
+    let alloc = cx.tcx.eval_static_initializer(def_id)?;
     Ok((const_alloc_to_llvm(cx, alloc), alloc))
 }
 

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -13,7 +13,7 @@ use rustc_ast as ast;
 use rustc_hir::lang_items::LangItem;
 use rustc_index::vec::Idx;
 use rustc_middle::mir;
-use rustc_middle::mir::interpret::{AllocId, ConstValue, Pointer, Scalar};
+use rustc_middle::mir::interpret::ConstValue;
 use rustc_middle::mir::AssertKind;
 use rustc_middle::ty::layout::{FnAbiExt, HasTyCtxt};
 use rustc_middle::ty::print::with_no_trimmed_paths;
@@ -867,24 +867,12 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         let ty = constant.literal.ty;
                         let size = bx.layout_of(ty).size;
                         let scalar = match const_value {
-                            // Promoted constants are evaluated into a ByRef instead of a Scalar,
-                            // but we want the scalar value here.
-                            ConstValue::ByRef { alloc, offset } => {
-                                let ptr = Pointer::new(AllocId(0), offset);
-                                alloc
-                                    .read_scalar(&bx, ptr, size)
-                                    .and_then(|s| s.check_init())
-                                    .unwrap_or_else(|e| {
-                                        bx.tcx().sess.span_err(
-                                            span,
-                                            &format!("Could not evaluate asm const: {}", e),
-                                        );
-
-                                        // We are erroring out, just emit a dummy constant.
-                                        Scalar::from_u64(0)
-                                    })
-                            }
-                            _ => span_bug!(span, "expected ByRef for promoted asm const"),
+                            ConstValue::Scalar(s) => s,
+                            _ => span_bug!(
+                                span,
+                                "expected Scalar for promoted asm const, but got {:#?}",
+                                const_value
+                            ),
                         };
                         let value = scalar.assert_bits(size);
                         let string = match ty.kind() {

compiler/rustc_infer/src/infer/mod.rs

@@ -21,7 +21,7 @@ use rustc_middle::infer::canonical::{Canonical, CanonicalVarValues};
 use rustc_middle::infer::unify_key::{ConstVarValue, ConstVariableValue};
 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind, ToType};
 use rustc_middle::mir;
-use rustc_middle::mir::interpret::ConstEvalResult;
+use rustc_middle::mir::interpret::EvalToConstValueResult;
 use rustc_middle::traits::select;
 use rustc_middle::ty::error::{ExpectedFound, TypeError, UnconstrainedNumeric};
 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder};
@@ -1542,7 +1542,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         substs: SubstsRef<'tcx>,
         promoted: Option<mir::Promoted>,
         span: Option<Span>,
-    ) -> ConstEvalResult<'tcx> {
+    ) -> EvalToConstValueResult<'tcx> {
         let mut original_values = OriginalQueryValues::default();
         let canonical = self.canonicalize_query(&(param_env, substs), &mut original_values);
 

compiler/rustc_lint/src/builtin.rs

@@ -1474,21 +1474,19 @@ declare_lint_pass!(
     UnusedBrokenConst => []
 );
 
-fn check_const(cx: &LateContext<'_>, body_id: hir::BodyId) {
-    let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
-    // trigger the query once for all constants since that will already report the errors
-    // FIXME: Use ensure here
-    let _ = cx.tcx.const_eval_poly(def_id);
-}
-
 impl<'tcx> LateLintPass<'tcx> for UnusedBrokenConst {
     fn check_item(&mut self, cx: &LateContext<'_>, it: &hir::Item<'_>) {
         match it.kind {
             hir::ItemKind::Const(_, body_id) => {
-                check_const(cx, body_id);
+                let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
+                // trigger the query once for all constants since that will already report the errors
+                // FIXME: Use ensure here
+                let _ = cx.tcx.const_eval_poly(def_id);
             }
             hir::ItemKind::Static(_, _, body_id) => {
-                check_const(cx, body_id);
+                let def_id = cx.tcx.hir().body_owner_def_id(body_id).to_def_id();
+                // FIXME: Use ensure here
+                let _ = cx.tcx.eval_static_initializer(def_id);
             }
             _ => {}
         }

compiler/rustc_middle/src/mir/interpret/error.rs

@@ -1,4 +1,4 @@
-use super::{AllocId, Pointer, RawConst, Scalar};
+use super::{AllocId, ConstAlloc, Pointer, Scalar};
 
 use crate::mir::interpret::ConstValue;
 use crate::ty::{layout, query::TyCtxtAt, tls, FnSig, Ty};
@@ -27,8 +27,8 @@ CloneTypeFoldableAndLiftImpls! {
     ErrorHandled,
 }
 
-pub type ConstEvalRawResult<'tcx> = Result<RawConst<'tcx>, ErrorHandled>;
-pub type ConstEvalResult<'tcx> = Result<ConstValue<'tcx>, ErrorHandled>;
+pub type EvalToAllocationRawResult<'tcx> = Result<ConstAlloc<'tcx>, ErrorHandled>;
+pub type EvalToConstValueResult<'tcx> = Result<ConstValue<'tcx>, ErrorHandled>;
 
 pub fn struct_error<'tcx>(tcx: TyCtxtAt<'tcx>, msg: &str) -> DiagnosticBuilder<'tcx> {
     struct_span_err!(tcx.sess, tcx.span, E0080, "{}", msg)

compiler/rustc_middle/src/mir/interpret/mod.rs

@@ -118,12 +118,12 @@ use crate::ty::subst::GenericArgKind;
 use crate::ty::{self, Instance, Ty, TyCtxt};
 
 pub use self::error::{
-    struct_error, CheckInAllocMsg, ConstEvalRawResult, ConstEvalResult, ErrorHandled, InterpError,
-    InterpErrorInfo, InterpResult, InvalidProgramInfo, MachineStopType, ResourceExhaustionInfo,
-    UndefinedBehaviorInfo, UninitBytesAccess, UnsupportedOpInfo,
+    struct_error, CheckInAllocMsg, ErrorHandled, EvalToAllocationRawResult, EvalToConstValueResult,
+    InterpError, InterpErrorInfo, InterpResult, InvalidProgramInfo, MachineStopType,
+    ResourceExhaustionInfo, UndefinedBehaviorInfo, UninitBytesAccess, UnsupportedOpInfo,
 };
 
-pub use self::value::{get_slice_bytes, ConstValue, RawConst, Scalar, ScalarMaybeUninit};
+pub use self::value::{get_slice_bytes, ConstAlloc, ConstValue, Scalar, ScalarMaybeUninit};
 
 pub use self::allocation::{Allocation, AllocationExtra, InitMask, Relocations};
 

compiler/rustc_middle/src/mir/interpret/queries.rs

@@ -1,4 +1,4 @@
-use super::{ConstEvalResult, ErrorHandled, GlobalId};
+use super::{ErrorHandled, EvalToConstValueResult, GlobalId};
 
 use crate::mir;
 use crate::ty::subst::{InternalSubsts, SubstsRef};
@@ -10,7 +10,7 @@ impl<'tcx> TyCtxt<'tcx> {
     /// Evaluates a constant without providing any substitutions. This is useful to evaluate consts
     /// that can't take any generic arguments like statics, const items or enum discriminants. If a
     /// generic parameter is used within the constant `ErrorHandled::ToGeneric` will be returned.
-    pub fn const_eval_poly(self, def_id: DefId) -> ConstEvalResult<'tcx> {
+    pub fn const_eval_poly(self, def_id: DefId) -> EvalToConstValueResult<'tcx> {
         // In some situations def_id will have substitutions within scope, but they aren't allowed
         // to be used. So we can't use `Instance::mono`, instead we feed unresolved substitutions
         // into `const_eval` which will return `ErrorHandled::ToGeneric` if any of them are
@@ -38,7 +38,7 @@ impl<'tcx> TyCtxt<'tcx> {
         substs: SubstsRef<'tcx>,
         promoted: Option<mir::Promoted>,
         span: Option<Span>,
-    ) -> ConstEvalResult<'tcx> {
+    ) -> EvalToConstValueResult<'tcx> {
         match ty::Instance::resolve_opt_const_arg(self, param_env, def, substs) {
             Ok(Some(instance)) => {
                 let cid = GlobalId { instance, promoted };
@@ -54,7 +54,7 @@ impl<'tcx> TyCtxt<'tcx> {
         param_env: ty::ParamEnv<'tcx>,
         instance: ty::Instance<'tcx>,
         span: Option<Span>,
-    ) -> ConstEvalResult<'tcx> {
+    ) -> EvalToConstValueResult<'tcx> {
         self.const_eval_global_id(param_env, GlobalId { instance, promoted: None }, span)
     }
 
@@ -64,14 +64,14 @@ impl<'tcx> TyCtxt<'tcx> {
         param_env: ty::ParamEnv<'tcx>,
         cid: GlobalId<'tcx>,
         span: Option<Span>,
-    ) -> ConstEvalResult<'tcx> {
+    ) -> EvalToConstValueResult<'tcx> {
         // Const-eval shouldn't depend on lifetimes at all, so we can erase them, which should
         // improve caching of queries.
         let inputs = self.erase_regions(&param_env.and(cid));
         if let Some(span) = span {
-            self.at(span).const_eval_validated(inputs)
+            self.at(span).eval_to_const_value_raw(inputs)
         } else {
-            self.const_eval_validated(inputs)
+            self.eval_to_const_value_raw(inputs)
         }
     }
 
@@ -94,7 +94,7 @@ impl<'tcx> TyCtxt<'tcx> {
         param_env: ty::ParamEnv<'tcx>,
     ) -> Result<&'tcx mir::Allocation, ErrorHandled> {
         trace!("eval_to_allocation: Need to compute {:?}", gid);
-        let raw_const = self.const_eval_raw(param_env.and(gid))?;
+        let raw_const = self.eval_to_allocation_raw(param_env.and(gid))?;
         Ok(self.global_alloc(raw_const.alloc_id).unwrap_memory())
     }
 }

compiler/rustc_middle/src/mir/interpret/value.rs

@@ -12,9 +12,9 @@ use crate::ty::{ParamEnv, Ty, TyCtxt};
 
 use super::{sign_extend, truncate, AllocId, Allocation, InterpResult, Pointer, PointerArithmetic};
 
-/// Represents the result of a raw const operation, pre-validation.
+/// Represents the result of const evaluation via the `eval_to_allocation` query.
 #[derive(Clone, HashStable)]
-pub struct RawConst<'tcx> {
+pub struct ConstAlloc<'tcx> {
     // the value lives here, at offset 0, and that allocation definitely is a `AllocKind::Memory`
     // (so you can use `AllocMap::unwrap_memory`).
     pub alloc_id: AllocId,

compiler/rustc_middle/src/query/mod.rs

@@ -707,32 +707,27 @@ rustc_queries! {
     }
 
     Other {
-        /// Evaluates a constant without running sanity checks.
+        /// Evaluates a constant and returns the computed allocation.
         ///
-        /// **Do not use this** outside const eval. Const eval uses this to break query cycles
-        /// during validation. Please add a comment to every use site explaining why using
-        /// `const_eval_validated` isn't sufficient. The returned constant also isn't in a suitable
-        /// form to be used outside of const eval.
-        query const_eval_raw(key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>)
-            -> ConstEvalRawResult<'tcx> {
+        /// **Do not use this** directly, use the `tcx.eval_static_initializer` wrapper.
+        query eval_to_allocation_raw(key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>)
+            -> EvalToAllocationRawResult<'tcx> {
             desc { |tcx|
-                "const-evaluating `{}`",
+                "const-evaluating + checking `{}`",
                 key.value.display(tcx)
             }
         }
 
-        /// Results of evaluating const items or constants embedded in
-        /// other items (such as enum variant explicit discriminants).
-        ///
-        /// In contrast to `const_eval_raw` this performs some validation on the constant, and
-        /// returns a proper constant that is usable by the rest of the compiler.
+        /// Evaluates const items or anonymous constants
+        /// (such as enum variant explicit discriminants or array lengths)
+        /// into a representation suitable for the type system and const generics.
         ///
         /// **Do not use this** directly, use one of the following wrappers: `tcx.const_eval_poly`,
         /// `tcx.const_eval_resolve`, `tcx.const_eval_instance`, or `tcx.const_eval_global_id`.
-        query const_eval_validated(key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>)
-            -> ConstEvalResult<'tcx> {
+        query eval_to_const_value_raw(key: ty::ParamEnvAnd<'tcx, GlobalId<'tcx>>)
+            -> EvalToConstValueResult<'tcx> {
             desc { |tcx|
-                "const-evaluating + checking `{}`",
+                "simplifying constant for the type system `{}`",
                 key.value.display(tcx)
             }
             cache_on_disk_if(_, opt_result) {

compiler/rustc_middle/src/ty/query/mod.rs

@@ -14,7 +14,7 @@ use crate::middle::resolve_lifetime::{ObjectLifetimeDefault, Region, ResolveLife
 use crate::middle::stability::{self, DeprecationEntry};
 use crate::mir;
 use crate::mir::interpret::GlobalId;
-use crate::mir::interpret::{ConstEvalRawResult, ConstEvalResult, ConstValue};
+use crate::mir::interpret::{ConstValue, EvalToAllocationRawResult, EvalToConstValueResult};
 use crate::mir::interpret::{LitToConstError, LitToConstInput};
 use crate::mir::mono::CodegenUnit;
 use crate::traits::query::{