From 6b95606a136bad2109253e5e32cc13b7ecbbc49e Mon Sep 17 00:00:00 2001 From: Eduard Burtescu Date: Tue, 23 Aug 2016 09:07:23 +0300 Subject: [PATCH] rustc_trans: do not generate allocas for unused locals. --- src/librustc_trans/mir/analyze.rs | 6 ++++++ src/test/run-pass/mir_heavy_promoted.rs | 18 ++++++++++++++++++ 2 files changed, 24 insertions(+) create mode 100644 src/test/run-pass/mir_heavy_promoted.rs diff --git a/src/librustc_trans/mir/analyze.rs b/src/librustc_trans/mir/analyze.rs index e0d959f4774..66eb78aef07 100644 --- a/src/librustc_trans/mir/analyze.rs +++ b/src/librustc_trans/mir/analyze.rs @@ -48,6 +48,12 @@ pub fn lvalue_locals<'bcx, 'tcx>(bcx: Block<'bcx,'tcx>, common::type_is_fat_ptr(bcx.tcx(), ty)); } else if common::type_is_imm_pair(bcx.ccx(), ty) { // We allow pairs and uses of any of their 2 fields. + } else if !analyzer.seen_assigned.contains(index) { + // No assignment has been seen, which means that + // either the local has been marked as lvalue + // already, or there is no possible initialization + // for the local, making any reads invalid. + // This is useful in weeding out dead temps. } else { // These sorts of types require an alloca. Note that // type_is_immediate() may *still* be true, particularly diff --git a/src/test/run-pass/mir_heavy_promoted.rs b/src/test/run-pass/mir_heavy_promoted.rs new file mode 100644 index 00000000000..9e033421574 --- /dev/null +++ b/src/test/run-pass/mir_heavy_promoted.rs @@ -0,0 +1,18 @@ +// Copyright 2016 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +const TEST_DATA: [u8; 32 * 1024 * 1024] = [42; 32 * 1024 * 1024]; + +// Check that the promoted copy of TEST_DATA doesn't +// leave an alloca from an unused temp behind, which, +// without optimizations, can still blow the stack. +fn main() { + println!("{}", TEST_DATA.len()); +}