From 4c577466098ccf79788456f4cf92107ff30aa231 Mon Sep 17 00:00:00 2001 From: Ralf Jung Date: Sun, 10 Mar 2024 12:39:53 +0100 Subject: [PATCH] add comments explaining where post-mono const eval errors abort compilation --- compiler/rustc_monomorphize/src/collector.rs | 9 ++++++--- compiler/rustc_monomorphize/src/partitioning.rs | 3 +++ 2 files changed, 9 insertions(+), 3 deletions(-) diff --git a/compiler/rustc_monomorphize/src/collector.rs b/compiler/rustc_monomorphize/src/collector.rs index 32f823a5ac68f..573a8f68347ec 100644 --- a/compiler/rustc_monomorphize/src/collector.rs +++ b/compiler/rustc_monomorphize/src/collector.rs @@ -814,13 +814,16 @@ impl<'a, 'tcx> MirVisitor<'tcx> for MirUsedCollector<'a, 'tcx> { self.super_rvalue(rvalue, location); } - /// This does not walk the constant, as it has been handled entirely here and trying - /// to walk it would attempt to evaluate the `ty::Const` inside, which doesn't necessarily - /// work, as some constants cannot be represented in the type system. + /// This does not walk the MIR of the constant as that is not needed for codegen, all we need is + /// to ensure that the constant evaluates successfully and walk the result. #[instrument(skip(self), level = "debug")] fn visit_constant(&mut self, constant: &mir::ConstOperand<'tcx>, location: Location) { let const_ = self.monomorphize(constant.const_); let param_env = ty::ParamEnv::reveal_all(); + // Evaluate the constant. This makes const eval failure a collection-time error (rather than + // a codegen-time error). rustc stops after collection if there was an error, so this + // ensures codegen never has to worry about failing consts. + // (codegen relies on this and ICEs will happen if this is violated.) let val = match const_.eval(self.tcx, param_env, None) { Ok(v) => v, Err(ErrorHandled::Reported(..)) => return, diff --git a/compiler/rustc_monomorphize/src/partitioning.rs b/compiler/rustc_monomorphize/src/partitioning.rs index 8bebc30e4356a..c9ebc73246048 100644 --- a/compiler/rustc_monomorphize/src/partitioning.rs +++ b/compiler/rustc_monomorphize/src/partitioning.rs @@ -1114,6 +1114,9 @@ fn collect_and_partition_mono_items(tcx: TyCtxt<'_>, (): ()) -> (&DefIdSet, &[Co let (items, usage_map) = collector::collect_crate_mono_items(tcx, collection_mode); + // If there was an error during collection (e.g. from one of the constants we evaluated), + // then we stop here. This way codegen does not have to worry about failing constants. + // (codegen relies on this and ICEs will happen if this is violated.) tcx.dcx().abort_if_errors(); let (codegen_units, _) = tcx.sess.time("partition_and_assert_distinct_symbols", || {