From d5769e9843dede495551a781cf947b631984868f Mon Sep 17 00:00:00 2001 From: Erik Desjardins Date: Sat, 19 Feb 2022 01:17:31 -0500 Subject: [PATCH] switch to limiting the number of init/uninit chunks --- compiler/rustc_codegen_llvm/src/consts.rs | 30 ++++++------------- compiler/rustc_interface/src/tests.rs | 2 +- .../src/mir/interpret/allocation.rs | 1 + compiler/rustc_session/src/options.rs | 6 ++-- src/test/codegen/uninit-consts.rs | 3 +- 5 files changed, 16 insertions(+), 26 deletions(-) diff --git a/compiler/rustc_codegen_llvm/src/consts.rs b/compiler/rustc_codegen_llvm/src/consts.rs index ddd87c5b24d..14de6c5986a 100644 --- a/compiler/rustc_codegen_llvm/src/consts.rs +++ b/compiler/rustc_codegen_llvm/src/consts.rs @@ -37,7 +37,7 @@ fn append_chunks_of_init_and_uninit_bytes<'ll, 'a, 'b>( alloc: &'a Allocation, range: Range, ) { - let mut chunks = alloc + let chunks = alloc .init_mask() .range_as_init_chunks(Size::from_bytes(range.start), Size::from_bytes(range.end)); @@ -53,32 +53,20 @@ fn append_chunks_of_init_and_uninit_bytes<'ll, 'a, 'b>( } }; - // Generating partially-uninit consts is limited to small allocations, + // Generating partially-uninit consts is limited to small numbers of chunks, // to avoid the cost of generating large complex const expressions. // For example, `[(u32, u8); 1024 * 1024]` contains uninit padding in each element, // and would result in `{ [5 x i8] zeroinitializer, [3 x i8] undef, ...repeat 1M times... }`. - let allow_partially_uninit = - match cx.sess().opts.debugging_opts.partially_uninit_const_threshold { - Some(max) => range.len() <= max, - None => false, - }; + let max = cx.sess().opts.debugging_opts.uninit_const_chunk_threshold; + let allow_uninit_chunks = chunks.clone().take(max.saturating_add(1)).count() <= max; - if allow_partially_uninit { + if allow_uninit_chunks { llvals.extend(chunks.map(chunk_to_llval)); } else { - let llval = match (chunks.next(), chunks.next()) { - (Some(chunk), None) => { - // exactly one chunk, either fully init or fully uninit - chunk_to_llval(chunk) - } - _ => { - // partially uninit, codegen as if it was initialized - // (using some arbitrary value for uninit bytes) - let bytes = alloc.inspect_with_uninit_and_ptr_outside_interpreter(range); - cx.const_bytes(bytes) - } - }; - llvals.push(llval); + // If this allocation contains any uninit bytes, codegen as if it was initialized + // (using some arbitrary value for uninit bytes). + let bytes = alloc.inspect_with_uninit_and_ptr_outside_interpreter(range); + llvals.push(cx.const_bytes(bytes)); } } diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs index 9ab138c1b12..def5c30411b 100644 --- a/compiler/rustc_interface/src/tests.rs +++ b/compiler/rustc_interface/src/tests.rs @@ -758,7 +758,6 @@ macro_rules! tracked { tracked!(osx_rpath_install_name, true); tracked!(panic_abort_tests, true); tracked!(panic_in_drop, PanicStrategy::Abort); - tracked!(partially_uninit_const_threshold, Some(123)); tracked!(pick_stable_methods_before_any_unstable, false); tracked!(plt, Some(true)); tracked!(polonius, true); @@ -789,6 +788,7 @@ macro_rules! tracked { tracked!(trap_unreachable, Some(false)); tracked!(treat_err_as_bug, NonZeroUsize::new(1)); tracked!(tune_cpu, Some(String::from("abc"))); + tracked!(uninit_const_chunk_threshold, 123); tracked!(unleash_the_miri_inside_of_you, true); tracked!(use_ctors_section, Some(true)); tracked!(verify_llvm_ir, true); diff --git a/compiler/rustc_middle/src/mir/interpret/allocation.rs b/compiler/rustc_middle/src/mir/interpret/allocation.rs index a36c9b6ed73..5de119f9562 100644 --- a/compiler/rustc_middle/src/mir/interpret/allocation.rs +++ b/compiler/rustc_middle/src/mir/interpret/allocation.rs @@ -957,6 +957,7 @@ pub fn range_as_init_chunks(&self, start: Size, end: Size) -> InitChunkIter<'_> } /// Yields [`InitChunk`]s. See [`InitMask::range_as_init_chunks`]. +#[derive(Clone)] pub struct InitChunkIter<'a> { init_mask: &'a InitMask, /// Whether the next chunk we will return is initialized. diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs index 59ce7cdb603..26bb268a039 100644 --- a/compiler/rustc_session/src/options.rs +++ b/compiler/rustc_session/src/options.rs @@ -1341,9 +1341,6 @@ mod parse { "panic strategy for panics in drops"), parse_only: bool = (false, parse_bool, [UNTRACKED], "parse only; do not compile, assemble, or link (default: no)"), - partially_uninit_const_threshold: Option = (Some(1024), parse_opt_number, [TRACKED], - "allow generating const initializers with mixed init/uninit bytes, \ - and set the maximum total size of a const allocation for which this is allowed (default: 1024 bytes)"), perf_stats: bool = (false, parse_bool, [UNTRACKED], "print some performance-related statistics (default: no)"), pick_stable_methods_before_any_unstable: bool = (true, parse_bool, [TRACKED], @@ -1488,6 +1485,9 @@ mod parse { "in diagnostics, use heuristics to shorten paths referring to items"), ui_testing: bool = (false, parse_bool, [UNTRACKED], "emit compiler diagnostics in a form suitable for UI testing (default: no)"), + uninit_const_chunk_threshold: usize = (256, parse_number, [TRACKED], + "allow generating const initializers with mixed init/uninit chunks, \ + and set the maximum number of chunks for which this is allowed (default: 256)"), unleash_the_miri_inside_of_you: bool = (false, parse_bool, [TRACKED], "take the brakes off const evaluation. NOTE: this is unsound (default: no)"), unpretty: Option = (None, parse_unpretty, [UNTRACKED], diff --git a/src/test/codegen/uninit-consts.rs b/src/test/codegen/uninit-consts.rs index 0ca2197ecbc..d8c8fce105f 100644 --- a/src/test/codegen/uninit-consts.rs +++ b/src/test/codegen/uninit-consts.rs @@ -15,7 +15,8 @@ pub struct PartiallyUninit { // CHECK: [[PARTIALLY_UNINIT:@[0-9]+]] = private unnamed_addr constant <{ [4 x i8], [12 x i8] }> <{ [4 x i8] c"\EF\BE\AD\DE", [12 x i8] undef }>, align 4 -// This shouldn't contain undef, since it's larger than the 1024 byte limit. +// This shouldn't contain undef, since it contains more than 256 chunks +// (the default value of uninit_const_chunk_threshold). // CHECK: [[UNINIT_PADDING_HUGE:@[0-9]+]] = private unnamed_addr constant <{ [32768 x i8] }> <{ [32768 x i8] c"{{.+}}" }>, align 4 // CHECK: [[FULLY_UNINIT_HUGE:@[0-9]+]] = private unnamed_addr constant <{ [16384 x i8] }> undef