From 35566bfd7dd2e316d190078703de54a4dadda062 Mon Sep 17 00:00:00 2001 From: Simon Vandel Sillesen Date: Sun, 3 Jan 2021 15:45:15 +0100 Subject: Do not emit alloca for ZST local even if it is uninitialized --- compiler/rustc_codegen_ssa/src/mir/analyze.rs | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) (limited to 'compiler/rustc_codegen_ssa') diff --git a/compiler/rustc_codegen_ssa/src/mir/analyze.rs b/compiler/rustc_codegen_ssa/src/mir/analyze.rs index 289629d9215..31d5c87182d 100644 --- a/compiler/rustc_codegen_ssa/src/mir/analyze.rs +++ b/compiler/rustc_codegen_ssa/src/mir/analyze.rs @@ -281,7 +281,18 @@ impl<'mir, 'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> Visitor<'tcx> Some(assignment_location) => { assignment_location.dominates(location, &self.dominators) } - None => false, + None => { + debug!("No first assignment found for {:?}", local); + // We have not seen any assignment to the local yet, + // but before marking not_ssa, check if it is a ZST, + // in which case we don't need to initialize the local. + let ty = self.fx.mir.local_decls[local].ty; + let ty = self.fx.monomorphize(ty); + + let is_zst = self.fx.cx.layout_of(ty).is_zst(); + debug!("is_zst: {}", is_zst); + is_zst + } }; if !ssa_read { self.not_ssa(local); -- cgit 1.4.1-3-g733a5