From 01510612ee20d14a3397427891a4042a34d53956 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Tomasz=20Mi=C4=85sko?= Date: Thu, 3 Sep 2020 00:00:00 +0000 Subject: [PATCH] NRVO: Allow occurrences of the return place in var debug info The non-use occurrence of the return place in var debug info does not currently inhibit NRVO optimization, but it will fail assertion in `visit_place` when optimization is performed. Relax assertion check to allow the return place in var debug info. This case might be impossible to hit in optimization pipelines as of now, but can be encountered in customized mir-opt-level=2 pipeline with copy propagation disabled. For example in: ``` pub fn b(s: String) -> String { a(s) } #[inline] pub fn a(s: String) -> String { let x = s; let y = x; y } ``` --- compiler/rustc_mir/src/transform/nrvo.rs | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/compiler/rustc_mir/src/transform/nrvo.rs b/compiler/rustc_mir/src/transform/nrvo.rs index 1f3d7bb7cc6f4..3673b6a4aa223 100644 --- a/compiler/rustc_mir/src/transform/nrvo.rs +++ b/compiler/rustc_mir/src/transform/nrvo.rs @@ -1,6 +1,6 @@ use rustc_hir::Mutability; use rustc_index::bit_set::HybridBitSet; -use rustc_middle::mir::visit::{MutVisitor, PlaceContext, Visitor}; +use rustc_middle::mir::visit::{MutVisitor, NonUseContext, PlaceContext, Visitor}; use rustc_middle::mir::{self, BasicBlock, Local, Location}; use rustc_middle::ty::TyCtxt; @@ -196,9 +196,10 @@ impl MutVisitor<'tcx> for RenameToReturnPlace<'tcx> { self.super_terminator(terminator, loc); } - fn visit_local(&mut self, l: &mut Local, _: PlaceContext, _: Location) { - assert_ne!(*l, mir::RETURN_PLACE); - if *l == self.to_rename { + fn visit_local(&mut self, l: &mut Local, ctxt: PlaceContext, _: Location) { + if *l == mir::RETURN_PLACE { + assert_eq!(ctxt, PlaceContext::NonUse(NonUseContext::VarDebugInfo)); + } else if *l == self.to_rename { *l = mir::RETURN_PLACE; } }