From a10402671bb83c7c6f33d0f37f4be6ff87ee63c4 Mon Sep 17 00:00:00 2001 From: Simonas Kazlauskas Date: Fri, 28 Sep 2018 17:40:06 +0300 Subject: [PATCH] Do not put noalias annotations by default This will be re-enabled sooner or later depending on results of further investigation. Fixes #54462 --- src/librustc_codegen_llvm/type_of.rs | 19 +++++++---- src/test/codegen/function-arguments.rs | 6 ++-- ...issue-54462-mutable-noalias-correctness.rs | 33 +++++++++++++++++++ 3 files changed, 48 insertions(+), 10 deletions(-) create mode 100644 src/test/run-pass/issue-54462-mutable-noalias-correctness.rs diff --git a/src/librustc_codegen_llvm/type_of.rs b/src/librustc_codegen_llvm/type_of.rs index 4728d7717a1e1..751c4ea5ce63f 100644 --- a/src/librustc_codegen_llvm/type_of.rs +++ b/src/librustc_codegen_llvm/type_of.rs @@ -10,11 +10,9 @@ use abi::{FnType, FnTypeExt}; use common::*; -use llvm; use rustc::hir; use rustc::ty::{self, Ty, TypeFoldable}; use rustc::ty::layout::{self, Align, LayoutOf, Size, TyLayout}; -use rustc_target::spec::PanicStrategy; use rustc_target::abi::FloatTy; use rustc_mir::monomorphize::item::DefPathBasedNames; use type_::Type; @@ -429,12 +427,19 @@ impl<'tcx> LayoutLlvmExt<'tcx> for TyLayout<'tcx> { PointerKind::Shared }, hir::MutMutable => { - // Only emit noalias annotations for LLVM >= 6 or in panic=abort - // mode, as prior versions had many bugs in conjunction with - // unwinding. See also issue #31681. + // Previously we would only emit noalias annotations for LLVM >= 6 or in + // panic=abort mode. That was deemed right, as prior versions had many bugs + // in conjunction with unwinding, but later versions didn’t seem to have + // said issues. See issue #31681. + // + // Alas, later on we encountered a case where noalias would generate wrong + // code altogether even with recent versions of LLVM in *safe* code with no + // unwinding involved. See #54462. + // + // For now, do not enable mutable_noalias by default at all, while the + // issue is being figured out. let mutable_noalias = cx.tcx.sess.opts.debugging_opts.mutable_noalias - .unwrap_or(unsafe { llvm::LLVMRustVersionMajor() >= 6 } - || cx.tcx.sess.panic_strategy() == PanicStrategy::Abort); + .unwrap_or(false); if mutable_noalias { PointerKind::UniqueBorrowed } else { diff --git a/src/test/codegen/function-arguments.rs b/src/test/codegen/function-arguments.rs index 0bd021f8ae2d6..5061d9a915e2e 100644 --- a/src/test/codegen/function-arguments.rs +++ b/src/test/codegen/function-arguments.rs @@ -53,13 +53,13 @@ pub fn named_borrow<'r>(_: &'r i32) { pub fn unsafe_borrow(_: &UnsafeInner) { } -// CHECK: @mutable_unsafe_borrow(i16* noalias dereferenceable(2) %arg0) +// CHECK: @mutable_unsafe_borrow(i16* dereferenceable(2) %arg0) // ... unless this is a mutable borrow, those never alias #[no_mangle] pub fn mutable_unsafe_borrow(_: &mut UnsafeInner) { } -// CHECK: @mutable_borrow(i32* noalias dereferenceable(4) %arg0) +// CHECK: @mutable_borrow(i32* dereferenceable(4) %arg0) // FIXME #25759 This should also have `nocapture` #[no_mangle] pub fn mutable_borrow(_: &mut i32) { @@ -102,7 +102,7 @@ pub fn helper(_: usize) { pub fn slice(_: &[u8]) { } -// CHECK: @mutable_slice([0 x i8]* noalias nonnull %arg0.0, [[USIZE]] %arg0.1) +// CHECK: @mutable_slice([0 x i8]* nonnull %arg0.0, [[USIZE]] %arg0.1) // FIXME #25759 This should also have `nocapture` #[no_mangle] pub fn mutable_slice(_: &mut [u8]) { diff --git a/src/test/run-pass/issue-54462-mutable-noalias-correctness.rs b/src/test/run-pass/issue-54462-mutable-noalias-correctness.rs new file mode 100644 index 0000000000000..f0e52b2928783 --- /dev/null +++ b/src/test/run-pass/issue-54462-mutable-noalias-correctness.rs @@ -0,0 +1,33 @@ +// Copyright 2018 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. +// +// compile-flags: -Ccodegen-units=1 -O + +fn linidx(row: usize, col: usize) -> usize { + row * 1 + col * 3 +} + +fn main() { + let mut mat = [1.0f32, 5.0, 9.0, 2.0, 6.0, 10.0, 3.0, 7.0, 11.0, 4.0, 8.0, 12.0]; + + for i in 0..2 { + for j in i+1..3 { + if mat[linidx(j, 3)] > mat[linidx(i, 3)] { + for k in 0..4 { + let (x, rest) = mat.split_at_mut(linidx(i, k) + 1); + let a = x.last_mut().unwrap(); + let b = rest.get_mut(linidx(j, k) - linidx(i, k) - 1).unwrap(); + ::std::mem::swap(a, b); + } + } + } + } + assert_eq!([9.0, 5.0, 1.0, 10.0, 6.0, 2.0, 11.0, 7.0, 3.0, 12.0, 8.0, 4.0], mat); +}