From 497794dc53b766598220494737aba5632b293164 Mon Sep 17 00:00:00 2001 From: Folkert de Vries Date: Sun, 8 Dec 2024 11:38:14 +0100 Subject: [PATCH] add `-Zmin-function-alignment` --- compiler/rustc_codegen_llvm/src/attributes.rs | 6 +++- compiler/rustc_interface/src/tests.rs | 2 ++ compiler/rustc_session/src/config.rs | 2 ++ compiler/rustc_session/src/options.rs | 19 ++++++++++++ tests/codegen/min-function-alignment.rs | 30 +++++++++++++++++++ 5 files changed, 58 insertions(+), 1 deletion(-) create mode 100644 tests/codegen/min-function-alignment.rs diff --git a/compiler/rustc_codegen_llvm/src/attributes.rs b/compiler/rustc_codegen_llvm/src/attributes.rs index cb958c1d4d771..3bd5515c33c85 100644 --- a/compiler/rustc_codegen_llvm/src/attributes.rs +++ b/compiler/rustc_codegen_llvm/src/attributes.rs @@ -480,7 +480,11 @@ pub(crate) fn llfn_attrs_from_instance<'ll, 'tcx>( let allocated_pointer = AttributeKind::AllocatedPointer.create_attr(cx.llcx); attributes::apply_to_llfn(llfn, AttributePlace::Argument(0), &[allocated_pointer]); } - if let Some(align) = codegen_fn_attrs.alignment { + // function alignment can be set globally with the `-Zmin-function-alignment=` flag; + // the alignment from a `#[repr(align())]` is used if it specifies a higher alignment. + if let Some(align) = + Ord::max(cx.tcx.sess.opts.unstable_opts.min_function_alignment, codegen_fn_attrs.alignment) + { llvm::set_alignment(llfn, align); } if let Some(backchain) = backchain_attr(cx) { diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs index e76e9ca9f8529..d03a577b0138d 100644 --- a/compiler/rustc_interface/src/tests.rs +++ b/compiler/rustc_interface/src/tests.rs @@ -25,6 +25,7 @@ use rustc_span::edition::{DEFAULT_EDITION, Edition}; use rustc_span::source_map::{RealFileLoader, SourceMapInputs}; use rustc_span::symbol::sym; use rustc_span::{FileName, SourceFileHashAlgorithm}; +use rustc_target::abi::Align; use rustc_target::spec::{ CodeModel, FramePointer, LinkerFlavorCli, MergeFunctions, OnBrokenPipe, PanicStrategy, RelocModel, RelroLevel, SanitizerSet, SplitDebuginfo, StackProtector, TlsModel, WasmCAbi, @@ -803,6 +804,7 @@ fn test_unstable_options_tracking_hash() { tracked!(location_detail, LocationDetail { file: true, line: false, column: false }); tracked!(maximal_hir_to_mir_coverage, true); tracked!(merge_functions, Some(MergeFunctions::Disabled)); + tracked!(min_function_alignment, Some(Align::EIGHT)); tracked!(mir_emit_retag, true); tracked!(mir_enable_passes, vec![("DestProp".to_string(), false)]); tracked!(mir_keep_place_mention, true); diff --git a/compiler/rustc_session/src/config.rs b/compiler/rustc_session/src/config.rs index cb6d539cdf940..fdf26d0c41755 100644 --- a/compiler/rustc_session/src/config.rs +++ b/compiler/rustc_session/src/config.rs @@ -2884,6 +2884,7 @@ pub(crate) mod dep_tracking { use std::num::NonZero; use std::path::PathBuf; + use rustc_abi::Align; use rustc_data_structures::fx::FxIndexMap; use rustc_data_structures::stable_hasher::Hash64; use rustc_errors::LanguageIdentifier; @@ -3003,6 +3004,7 @@ pub(crate) mod dep_tracking { InliningThreshold, FunctionReturn, WasmCAbi, + Align, ); impl DepTrackingHash for (T1, T2) diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs index b01d9e5e8e3ac..da4329e6908fe 100644 --- a/compiler/rustc_session/src/options.rs +++ b/compiler/rustc_session/src/options.rs @@ -4,6 +4,7 @@ use std::num::{IntErrorKind, NonZero}; use std::path::PathBuf; use std::str; +use rustc_abi::Align; use rustc_data_structures::fx::FxIndexMap; use rustc_data_structures::profiling::TimePassesFormat; use rustc_data_structures::stable_hasher::Hash64; @@ -453,6 +454,7 @@ mod desc { pub(crate) const parse_wasm_c_abi: &str = "`legacy` or `spec`"; pub(crate) const parse_mir_include_spans: &str = "either a boolean (`yes`, `no`, `on`, `off`, etc), or `nll` (default: `nll`)"; + pub(crate) const parse_align: &str = "a number that is a power of 2 between 1 and 2^29"; } pub mod parse { @@ -1521,6 +1523,21 @@ pub mod parse { true } + + pub(crate) fn parse_align(slot: &mut Option, v: Option<&str>) -> bool { + let mut bytes = 0u64; + if !parse_number(&mut bytes, v) { + return false; + } + + let Ok(align) = Align::from_bytes(bytes) else { + return false; + }; + + *slot = Some(align); + + true + } } options! { @@ -1876,6 +1893,8 @@ options! { "gather metadata statistics (default: no)"), metrics_dir: Option = (None, parse_opt_pathbuf, [UNTRACKED], "the directory metrics emitted by rustc are dumped into (implicitly enables default set of metrics)"), + min_function_alignment: Option = (None, parse_align, [TRACKED], + "align all functions to at least this many bytes. Must be a power of 2"), mir_emit_retag: bool = (false, parse_bool, [TRACKED], "emit Retagging MIR statements, interpreted e.g., by miri; implies -Zmir-opt-level=0 \ (default: no)"), diff --git a/tests/codegen/min-function-alignment.rs b/tests/codegen/min-function-alignment.rs new file mode 100644 index 0000000000000..48d32228b64ba --- /dev/null +++ b/tests/codegen/min-function-alignment.rs @@ -0,0 +1,30 @@ +//@ compile-flags: -C no-prepopulate-passes -Z mir-opt-level=0 -Zmin-function-alignment=16 + +#![crate_type = "lib"] +#![feature(fn_align)] + +// functions without explicit alignment use the global minimum +// +// CHECK: align 16 +#[no_mangle] +pub fn no_explicit_align() {} + +// CHECK: align 16 +#[no_mangle] +#[repr(align(8))] +pub fn lower_align() {} + +// CHECK: align 32 +#[no_mangle] +#[repr(align(32))] +pub fn higher_align() {} + +// cold functions follow the same rules as other functions +// +// in GCC, the `-falign-functions` does not apply to cold functions, but +// `-Zmin-function-alignment` applies to all functions. +// +// CHECK: align 16 +#[no_mangle] +#[cold] +pub fn no_explicit_align_cold() {}