Auto merge of rust-lang#115748 - RalfJung:post-mono, r=<try>

move required_consts check to general post-mono-check function

I was hoping this would simplify the code. That didn't entirely happen, but I still think it could be useful to have a single place for the "required const" check -- and this does simplify some code in codegen, where the const-eval functions no longer have to return a `Result`.

Also this is in preparation for another post-mono check that will be needed for (the current hackfix for) rust-lang#115709: ensuring that all locals are dynamically sized.

I didn't expect this to change diagnostics, but the changes seem either harmless (for the cycle errors) or improvements (where more spans are shown when something goes wrong in a constant).

r? `@oli-obk`

compiler/rustc_codegen_cranelift/src/base.rs

@@ -250,7 +250,10 @@ pub(crate) fn verify_func(
 }
 
 fn codegen_fn_body(fx: &mut FunctionCx<'_, '_, '_>, start_block: Block) {
-    if !crate::constant::check_constants(fx) {
+    if let Err(err) =
+        fx.mir.post_mono_checks(fx.tcx, ty::ParamEnv::reveal_all(), |c| Ok(fx.monomorphize(c)))
+    {
+        err.emit_err(fx.tcx);
         fx.bcx.append_block_params_for_function_params(fx.block_map[START_BLOCK]);
         fx.bcx.switch_to_block(fx.block_map[START_BLOCK]);
         // compilation should have been aborted

compiler/rustc_codegen_cranelift/src/constant.rs

@@ -2,9 +2,7 @@
 
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
-use rustc_middle::mir::interpret::{
-    read_target_uint, AllocId, ConstValue, ErrorHandled, GlobalAlloc, Scalar,
-};
+use rustc_middle::mir::interpret::{read_target_uint, AllocId, ConstValue, GlobalAlloc, Scalar};
 
 use cranelift_module::*;
 
@@ -33,16 +31,6 @@ impl ConstantCx {
     }
 }
 
-pub(crate) fn check_constants(fx: &mut FunctionCx<'_, '_, '_>) -> bool {
-    let mut all_constants_ok = true;
-    for constant in &fx.mir.required_consts {
-        if eval_mir_constant(fx, constant).is_none() {
-            all_constants_ok = false;
-        }
-    }
-    all_constants_ok
-}
-
 pub(crate) fn codegen_static(tcx: TyCtxt<'_>, module: &mut dyn Module, def_id: DefId) {
     let mut constants_cx = ConstantCx::new();
     constants_cx.todo.push(TodoItem::Static(def_id));
@@ -76,30 +64,20 @@ pub(crate) fn codegen_tls_ref<'tcx>(
 pub(crate) fn eval_mir_constant<'tcx>(
     fx: &FunctionCx<'_, '_, 'tcx>,
     constant: &Constant<'tcx>,
-) -> Option<(ConstValue<'tcx>, Ty<'tcx>)> {
+) -> (ConstValue<'tcx>, Ty<'tcx>) {
     let cv = fx.monomorphize(constant.literal);
+    // This cannot fail because we checked all required_consts in advance.
     let val = cv
         .eval(fx.tcx, ty::ParamEnv::reveal_all(), Some(constant.span))
-        .map_err(|err| match err {
-            ErrorHandled::Reported(_) => {
-                fx.tcx.sess.span_err(constant.span, "erroneous constant encountered");
-            }
-            ErrorHandled::TooGeneric => {
-                span_bug!(constant.span, "codegen encountered polymorphic constant: {:?}", err);
-            }
-        })
-        .ok();
-    val.map(|val| (val, cv.ty()))
+        .expect("erroneous constant not captured by required_consts");
+    (val, cv.ty())
 }
 
 pub(crate) fn codegen_constant_operand<'tcx>(
     fx: &mut FunctionCx<'_, '_, 'tcx>,
     constant: &Constant<'tcx>,
 ) -> CValue<'tcx> {
-    let (const_val, ty) = eval_mir_constant(fx, constant).unwrap_or_else(|| {
-        span_bug!(constant.span, "erroneous constant not captured by required_consts")
-    });
-
+    let (const_val, ty) = eval_mir_constant(fx, constant);
     codegen_const_value(fx, const_val, ty)
 }
 
@@ -459,7 +437,7 @@ pub(crate) fn mir_operand_get_const_val<'tcx>(
     operand: &Operand<'tcx>,
 ) -> Option<ConstValue<'tcx>> {
     match operand {
-        Operand::Constant(const_) => Some(eval_mir_constant(fx, const_).unwrap().0),
+        Operand::Constant(const_) => Some(eval_mir_constant(fx, const_).0),
         // FIXME(rust-lang/rust#85105): Casts like `IMM8 as u32` result in the const being stored
         // inside a temporary before being passed to the intrinsic requiring the const argument.
         // This code tries to find a single constant defining definition of the referenced local.

compiler/rustc_codegen_cranelift/src/inline_asm.rs

@@ -242,8 +242,7 @@ pub(crate) fn codegen_inline_asm<'tcx>(
                 }
             }
             InlineAsmOperand::Const { ref value } => {
-                let (const_value, ty) = crate::constant::eval_mir_constant(fx, value)
-                    .unwrap_or_else(|| span_bug!(span, "asm const cannot be resolved"));
+                let (const_value, ty) = crate::constant::eval_mir_constant(fx, value);
                 let value = rustc_codegen_ssa::common::asm_const_to_str(
                     fx.tcx,
                     span,

compiler/rustc_codegen_ssa/messages.ftl

@@ -19,8 +19,6 @@ codegen_ssa_copy_path_buf = unable to copy {$source_file} to {$output_path}: {$e
 
 codegen_ssa_create_temp_dir = couldn't create a temp dir: {$error}
 
-codegen_ssa_erroneous_constant = erroneous constant encountered
-
 codegen_ssa_error_creating_remark_dir = failed to create remark directory: {$error}
 
 codegen_ssa_expected_coverage_symbol = expected `coverage(off)` or `coverage(on)`
@@ -174,8 +172,6 @@ codegen_ssa_no_natvis_directory = error enumerating natvis directory: {$error}
 
 codegen_ssa_option_gcc_only = option `-Z gcc-ld` is used even though linker flavor is not gcc
 
-codegen_ssa_polymorphic_constant_too_generic = codegen encountered polymorphic constant: TooGeneric
-
 codegen_ssa_processing_dymutil_failed = processing debug info with `dsymutil` failed: {$status}
     .note = {$output}
 

compiler/rustc_codegen_ssa/src/errors.rs

@@ -595,20 +595,6 @@ pub struct InvalidWindowsSubsystem {
     pub subsystem: Symbol,
 }
 
-#[derive(Diagnostic)]
-#[diag(codegen_ssa_erroneous_constant)]
-pub struct ErroneousConstant {
-    #[primary_span]
-    pub span: Span,
-}
-
-#[derive(Diagnostic)]
-#[diag(codegen_ssa_polymorphic_constant_too_generic)]
-pub struct PolymorphicConstantTooGeneric {
-    #[primary_span]
-    pub span: Span,
-}
-
 #[derive(Diagnostic)]
 #[diag(codegen_ssa_shuffle_indices_evaluation)]
 pub struct ShuffleIndicesEvaluation {

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -1088,9 +1088,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     InlineAsmOperandRef::InOut { reg, late, in_value, out_place }
                 }
                 mir::InlineAsmOperand::Const { ref value } => {
-                    let const_value = self
-                        .eval_mir_constant(value)
-                        .unwrap_or_else(|_| span_bug!(span, "asm const cannot be resolved"));
+                    let const_value = self.eval_mir_constant(value);
                     let string = common::asm_const_to_str(
                         bx.tcx(),
                         span,

compiler/rustc_codegen_ssa/src/mir/constant.rs

@@ -14,34 +14,16 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         &self,
         bx: &mut Bx,
         constant: &mir::Constant<'tcx>,
-    ) -> Result<OperandRef<'tcx, Bx::Value>, ErrorHandled> {
-        let val = self.eval_mir_constant(constant)?;
+    ) -> OperandRef<'tcx, Bx::Value> {
+        let val = self.eval_mir_constant(constant);
         let ty = self.monomorphize(constant.ty());
-        Ok(OperandRef::from_const(bx, val, ty))
+        OperandRef::from_const(bx, val, ty)
     }
 
-    pub fn eval_mir_constant(
-        &self,
-        constant: &mir::Constant<'tcx>,
-    ) -> Result<ConstValue<'tcx>, ErrorHandled> {
+    pub fn eval_mir_constant(&self, constant: &mir::Constant<'tcx>) -> ConstValue<'tcx> {
         self.monomorphize(constant.literal)
             .eval(self.cx.tcx(), ty::ParamEnv::reveal_all(), Some(constant.span))
-            .map_err(|err| {
-                match err {
-                    ErrorHandled::Reported(_) => {
-                        self.cx
-                            .tcx()
-                            .sess
-                            .emit_err(errors::ErroneousConstant { span: constant.span });
-                    }
-                    ErrorHandled::TooGeneric => {
-                        self.cx.tcx().sess.diagnostic().emit_bug(
-                            errors::PolymorphicConstantTooGeneric { span: constant.span },
-                        );
-                    }
-                }
-                err
-            })
+            .expect("erroneous constant not captured by required_consts")
     }
 
     /// This is a convenience helper for `simd_shuffle_indices`. It has the precondition

compiler/rustc_codegen_ssa/src/mir/debuginfo.rs

@@ -579,23 +579,12 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     if let Some(dbg_var) = dbg_var {
                         let Some(dbg_loc) = self.dbg_loc(var.source_info) else { continue };
 
-                        if let Ok(operand) = self.eval_mir_constant_to_operand(bx, &c) {
-                            self.set_debug_loc(bx, var.source_info);
-                            let base = Self::spill_operand_to_stack(
-                                operand,
-                                Some(var.name.to_string()),
-                                bx,
-                            );
-
-                            bx.dbg_var_addr(
-                                dbg_var,
-                                dbg_loc,
-                                base.llval,
-                                Size::ZERO,
-                                &[],
-                                fragment,
-                            );
-                        }
+                        let operand = self.eval_mir_constant_to_operand(bx, &c);
+                        self.set_debug_loc(bx, var.source_info);
+                        let base =
+                            Self::spill_operand_to_stack(operand, Some(var.name.to_string()), bx);
+
+                        bx.dbg_var_addr(dbg_var, dbg_loc, base.llval, Size::ZERO, &[], fragment);
                     }
                 }
             }

compiler/rustc_codegen_ssa/src/mir/mod.rs

@@ -3,7 +3,6 @@ use crate::traits::*;
 use rustc_index::bit_set::BitSet;
 use rustc_index::IndexVec;
 use rustc_middle::mir;
-use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::mir::traversal;
 use rustc_middle::mir::UnwindTerminateReason;
 use rustc_middle::ty::layout::{FnAbiOf, HasTyCtxt, TyAndLayout};
@@ -212,23 +211,14 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 
     fx.per_local_var_debug_info = fx.compute_per_local_var_debug_info(&mut start_bx);
 
-    // Evaluate all required consts; codegen later assumes that CTFE will never fail.
-    let mut all_consts_ok = true;
-    for const_ in &mir.required_consts {
-        if let Err(err) = fx.eval_mir_constant(const_) {
-            all_consts_ok = false;
-            match err {
-                // errored or at least linted
-                ErrorHandled::Reported(_) => {}
-                ErrorHandled::TooGeneric => {
-                    span_bug!(const_.span, "codegen encountered polymorphic constant: {:?}", err)
-                }
-            }
-        }
-    }
-    if !all_consts_ok {
-        // We leave the IR in some half-built state here, and rely on this code not even being
-        // submitted to LLVM once an error was raised.
+    // Rust post-monomorphization checks; we later rely on them.
+    if let Err(err) =
+        mir.post_mono_checks(cx.tcx(), ty::ParamEnv::reveal_all(), |c| Ok(fx.monomorphize(c)))
+    {
+        err.emit_err(cx.tcx());
+        // This IR shouldn't ever be emitted, but let's try to guard against any of this code
+        // ever running.
+        start_bx.abort();
         return;
     }
 

compiler/rustc_codegen_ssa/src/mir/operand.rs

@@ -575,12 +575,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 self.codegen_consume(bx, place.as_ref())
             }
 
-            mir::Operand::Constant(ref constant) => {
-                // This cannot fail because we checked all required_consts in advance.
-                self.eval_mir_constant_to_operand(bx, constant).unwrap_or_else(|_err| {
-                    span_bug!(constant.span, "erroneous constant not captured by required_consts")
-                })
-            }
+            mir::Operand::Constant(ref constant) => self.eval_mir_constant_to_operand(bx, constant),
         }
     }
 }

compiler/rustc_const_eval/messages.ftl

@@ -83,9 +83,6 @@ const_eval_dyn_call_vtable_mismatch =
 const_eval_dyn_star_call_vtable_mismatch =
     `dyn*` call on a pointer whose vtable does not match its type
 
-const_eval_erroneous_constant =
-    erroneous constant used
-
 const_eval_error = {$error_kind ->
     [static] could not evaluate static initializer
     [const] evaluation of constant value failed

compiler/rustc_const_eval/src/const_eval/error.rs

@@ -4,7 +4,7 @@ use rustc_errors::{DiagnosticArgValue, DiagnosticMessage, IntoDiagnostic, IntoDi
 use rustc_middle::mir::AssertKind;
 use rustc_middle::ty::TyCtxt;
 use rustc_middle::ty::{layout::LayoutError, ConstInt};
-use rustc_span::{ErrorGuaranteed, Span, Symbol};
+use rustc_span::{ErrorGuaranteed, Span, Symbol, DUMMY_SP};
 
 use super::InterpCx;
 use crate::errors::{self, FrameNote, ReportErrorExt};
@@ -134,11 +134,11 @@ where
         // Don't emit a new diagnostic for these errors, they are already reported elsewhere or
         // should remain silent.
         err_inval!(Layout(LayoutError::Unknown(_))) | err_inval!(TooGeneric) => {
-            ErrorHandled::TooGeneric
+            ErrorHandled::TooGeneric(span.unwrap_or(DUMMY_SP))
         }
-        err_inval!(AlreadyReported(guar)) => ErrorHandled::Reported(guar),
+        err_inval!(AlreadyReported(guar)) => ErrorHandled::Reported(guar, span.unwrap_or(DUMMY_SP)),
         err_inval!(Layout(LayoutError::ReferencesError(guar))) => {
-            ErrorHandled::Reported(guar.into())
+            ErrorHandled::Reported(guar.into(), span.unwrap_or(DUMMY_SP))
         }
         // Report remaining errors.
         _ => {
@@ -152,7 +152,7 @@ where
 
             // Use *our* span to label the interp error
             err.span_label(our_span, msg);
-            ErrorHandled::Reported(err.emit().into())
+            ErrorHandled::Reported(err.emit().into(), span)
         }
     }
 }

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -212,7 +212,7 @@ pub fn eval_to_const_value_raw_provider<'tcx>(
         key.param_env = key.param_env.with_user_facing();
         match tcx.eval_to_const_value_raw(key) {
             // try again with reveal all as requested
-            Err(ErrorHandled::TooGeneric) => {}
+            Err(ErrorHandled::TooGeneric(_)) => {}
             // deduplicate calls
             other => return other,
         }
@@ -259,7 +259,7 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
         key.param_env = key.param_env.with_user_facing();
         match tcx.eval_to_allocation_raw(key) {
             // try again with reveal all as requested
-            Err(ErrorHandled::TooGeneric) => {}
+            Err(ErrorHandled::TooGeneric(_)) => {}
             // deduplicate calls
             other => return other,
         }

compiler/rustc_const_eval/src/errors.rs

@@ -239,13 +239,6 @@ pub struct LongRunningWarn {
     pub item_span: Span,
 }
 
-#[derive(Diagnostic)]
-#[diag(const_eval_erroneous_constant)]
-pub(crate) struct ErroneousConstUsed {
-    #[primary_span]
-    pub span: Span,
-}
-
 #[derive(Subdiagnostic)]
 #[note(const_eval_non_const_impl)]
 pub(crate) struct NonConstImplNote {