diff --git a/compiler/rustc_codegen_llvm/src/consts.rs b/compiler/rustc_codegen_llvm/src/consts.rs index 6707de933522b..9ab822f01f1ec 100644 --- a/compiler/rustc_codegen_llvm/src/consts.rs +++ b/compiler/rustc_codegen_llvm/src/consts.rs @@ -2,6 +2,7 @@ use crate::base; use crate::common::CodegenCx; use crate::debuginfo; use crate::llvm::{self, True}; +use crate::llvm_util; use crate::type_::Type; use crate::type_of::LayoutLlvmExt; use crate::value::Value; @@ -37,7 +38,7 @@ pub fn const_alloc_to_llvm<'ll>(cx: &CodegenCx<'ll, '_>, alloc: &Allocation) -> 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)); @@ -53,30 +54,26 @@ pub fn const_alloc_to_llvm<'ll>(cx: &CodegenCx<'ll, '_>, alloc: &Allocation) -> } }; - // Generating partially-uninit consts inhibits optimizations, so it is disabled by default. - // See https://github.com/rust-lang/rust/issues/84565. - let allow_partially_uninit = - match cx.sess().opts.debugging_opts.partially_uninit_const_threshold { - Some(max) => range.len() <= max, - None => false, - }; + // 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 max = if llvm_util::get_version() < (14, 0, 0) { + // Generating partially-uninit consts inhibits optimizations in LLVM < 14. + // See https://github.com/rust-lang/rust/issues/84565. + 1 + } else { + 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 9ab138c1b12a5..def5c30411b84 100644 --- a/compiler/rustc_interface/src/tests.rs +++ b/compiler/rustc_interface/src/tests.rs @@ -758,7 +758,6 @@ fn test_debugging_options_tracking_hash() { 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 @@ fn test_debugging_options_tracking_hash() { 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 a36c9b6ed7304..5de119f956282 100644 --- a/compiler/rustc_middle/src/mir/interpret/allocation.rs +++ b/compiler/rustc_middle/src/mir/interpret/allocation.rs @@ -957,6 +957,7 @@ impl InitMask { } /// 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 c069144fa9f1c..11204df7aeaa0 100644 --- a/compiler/rustc_session/src/options.rs +++ b/compiler/rustc_session/src/options.rs @@ -1341,9 +1341,6 @@ options! { "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 = (None, 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: never)"), 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 @@ options! { "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 = (16, 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: 16)"), 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/consts.rs b/src/test/codegen/consts.rs index 7f945299c22a6..1a84f1a44795b 100644 --- a/src/test/codegen/consts.rs +++ b/src/test/codegen/consts.rs @@ -1,5 +1,5 @@ // compile-flags: -C no-prepopulate-passes -// +// min-llvm-version: 14.0 #![crate_type = "lib"] @@ -43,7 +43,7 @@ pub fn inline_enum_const() -> E { #[no_mangle] pub fn low_align_const() -> E { // Check that low_align_const and high_align_const use the same constant - // CHECK: memcpy.p0i8.p0i8.i{{(32|64)}}(i8* align 2 %1, i8* align 2 getelementptr inbounds (<{ [8 x i8] }>, <{ [8 x i8] }>* [[LOW_HIGH]], i32 0, i32 0, i32 0), i{{(32|64)}} 8, i1 false) + // CHECK: memcpy.p0i8.p0i8.i{{(32|64)}}(i8* align 2 %1, i8* align 2 getelementptr inbounds (<{ [4 x i8], [4 x i8] }>, <{ [4 x i8], [4 x i8] }>* [[LOW_HIGH]], i32 0, i32 0, i32 0), i{{(32|64)}} 8, i1 false) *&E::A(0) } @@ -51,6 +51,6 @@ pub fn low_align_const() -> E { #[no_mangle] pub fn high_align_const() -> E { // Check that low_align_const and high_align_const use the same constant - // CHECK: memcpy.p0i8.p0i8.i{{(32|64)}}(i8* align 4 %1, i8* align 4 getelementptr inbounds (<{ [8 x i8] }>, <{ [8 x i8] }>* [[LOW_HIGH]], i32 0, i32 0, i32 0), i{{(32|64)}} 8, i1 false) + // CHECK: memcpy.p0i8.p0i8.i{{(32|64)}}(i8* align 4 %1, i8* align 4 getelementptr inbounds (<{ [4 x i8], [4 x i8] }>, <{ [4 x i8], [4 x i8] }>* [[LOW_HIGH]], i32 0, i32 0, i32 0), i{{(32|64)}} 8, i1 false) *&E::A(0) } diff --git a/src/test/codegen/uninit-consts-allow-partially-uninit.rs b/src/test/codegen/uninit-consts-allow-partially-uninit.rs deleted file mode 100644 index f7420e4126ed0..0000000000000 --- a/src/test/codegen/uninit-consts-allow-partially-uninit.rs +++ /dev/null @@ -1,35 +0,0 @@ -// compile-flags: -C no-prepopulate-passes -Z partially_uninit_const_threshold=1024 - -// Like uninit-consts.rs, but tests that we correctly generate partially-uninit consts -// when the (disabled by default) partially_uninit_const_threshold flag is used. - -#![crate_type = "lib"] - -use std::mem::MaybeUninit; - -pub struct PartiallyUninit { - x: u32, - y: MaybeUninit<[u8; 10]> -} - -// This should be partially undef. -// 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. -// CHECK: [[UNINIT_PADDING_HUGE:@[0-9]+]] = private unnamed_addr constant <{ [32768 x i8] }> <{ [32768 x i8] c"{{.+}}" }>, align 4 - -// CHECK-LABEL: @partially_uninit -#[no_mangle] -pub const fn partially_uninit() -> PartiallyUninit { - const X: PartiallyUninit = PartiallyUninit { x: 0xdeadbeef, y: MaybeUninit::uninit() }; - // CHECK: call void @llvm.memcpy.p0i8.p0i8.i{{(32|64)}}(i8* align 4 %1, i8* align 4 getelementptr inbounds (<{ [4 x i8], [12 x i8] }>, <{ [4 x i8], [12 x i8] }>* [[PARTIALLY_UNINIT]], i32 0, i32 0, i32 0), i{{(32|64)}} 16, i1 false) - X -} - -// CHECK-LABEL: @uninit_padding_huge -#[no_mangle] -pub const fn uninit_padding_huge() -> [(u32, u8); 4096] { - const X: [(u32, u8); 4096] = [(123, 45); 4096]; - // CHECK: call void @llvm.memcpy.p0i8.p0i8.i{{(32|64)}}(i8* align 4 %1, i8* align 4 getelementptr inbounds (<{ [32768 x i8] }>, <{ [32768 x i8] }>* [[UNINIT_PADDING_HUGE]], i32 0, i32 0, i32 0), i{{(32|64)}} 32768, i1 false) - X -} diff --git a/src/test/codegen/uninit-consts.rs b/src/test/codegen/uninit-consts.rs index c4c21e03f1676..3e370c7ba64f8 100644 --- a/src/test/codegen/uninit-consts.rs +++ b/src/test/codegen/uninit-consts.rs @@ -1,4 +1,5 @@ // compile-flags: -C no-prepopulate-passes +// min-llvm-version: 14.0 // Check that we use undef (and not zero) for uninitialized bytes in constants. @@ -12,7 +13,13 @@ pub struct PartiallyUninit { } // CHECK: [[FULLY_UNINIT:@[0-9]+]] = private unnamed_addr constant <{ [10 x i8] }> undef -// CHECK: [[PARTIALLY_UNINIT:@[0-9]+]] = private unnamed_addr constant <{ [16 x i8] }> <{ [16 x i8] c"\EF\BE\AD\DE\00\00\00\00\00\00\00\00\00\00\00\00" }>, align 4 + +// 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 contains more chunks +// than 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 // CHECK-LABEL: @fully_uninit @@ -27,7 +34,15 @@ pub const fn fully_uninit() -> MaybeUninit<[u8; 10]> { #[no_mangle] pub const fn partially_uninit() -> PartiallyUninit { const X: PartiallyUninit = PartiallyUninit { x: 0xdeadbeef, y: MaybeUninit::uninit() }; - // CHECK: call void @llvm.memcpy.p0i8.p0i8.i{{(32|64)}}(i8* align 4 %1, i8* align 4 getelementptr inbounds (<{ [16 x i8] }>, <{ [16 x i8] }>* [[PARTIALLY_UNINIT]], i32 0, i32 0, i32 0), i{{(32|64)}} 16, i1 false) + // CHECK: call void @llvm.memcpy.p0i8.p0i8.i{{(32|64)}}(i8* align 4 %1, i8* align 4 getelementptr inbounds (<{ [4 x i8], [12 x i8] }>, <{ [4 x i8], [12 x i8] }>* [[PARTIALLY_UNINIT]], i32 0, i32 0, i32 0), i{{(32|64)}} 16, i1 false) + X +} + +// CHECK-LABEL: @uninit_padding_huge +#[no_mangle] +pub const fn uninit_padding_huge() -> [(u32, u8); 4096] { + const X: [(u32, u8); 4096] = [(123, 45); 4096]; + // CHECK: call void @llvm.memcpy.p0i8.p0i8.i{{(32|64)}}(i8* align 4 %1, i8* align 4 getelementptr inbounds (<{ [32768 x i8] }>, <{ [32768 x i8] }>* [[UNINIT_PADDING_HUGE]], i32 0, i32 0, i32 0), i{{(32|64)}} 32768, i1 false) X }