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Auto merge of #87402 - nagisa:nagisa/request-feature-requests-for-features, r=estebank

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Direct users towards using Rust target feature names in CLI

This PR consists of a couple of changes on how we handle target features.

In particular there is a bug-fix wherein we avoid passing through features that aren't prefixed by `+` or `-` to LLVM. These appear to be causing LLVM to assert, which is pretty poor a behaviour (and also makes it pretty clear we expect feature names to be prefixed).

The other commit, I anticipate to be somewhat more controversial is outputting a warning when users specify a LLVM-specific, or otherwise unknown, feature name on the CLI. In those situations we request users to either replace it with a known Rust feature name (e.g. `bmi` -> `bmi1`) or file a feature request. I've a couple motivations for this: first of all, if users are specifying these features on the command line, I'm pretty confident there is also a need for these features to be usable via `#[cfg(target_feature)]` machinery.  And second, we're growing a fair number of backends recently and having ability to provide some sort of unified-ish interface in this place seems pretty useful to me.

Sponsored by: standard.ai
This commit is contained in:
bors 2022-03-02 03:03:22 +00:00
commit 39a3b52767
22 changed files with 253 additions and 108 deletions
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26
compiler/rustc_codegen_llvm/src/attributes.rs
View file

@ -79,13 +79,11 @@ pub fn sanitize_attrs<'ll>(
}
if enabled.contains(SanitizerSet::MEMTAG) {
// Check to make sure the mte target feature is actually enabled.
let sess = cx.tcx.sess;
let features = llvm_util::llvm_global_features(sess).join(",");
let mte_feature_enabled = features.rfind("+mte");
let mte_feature_disabled = features.rfind("-mte");
if mte_feature_enabled.is_none() || (mte_feature_disabled > mte_feature_enabled) {
sess.err("`-Zsanitizer=memtag` requires `-Ctarget-feature=+mte`");
let features = cx.tcx.global_backend_features(());
let mte_feature =
features.iter().map(|s| &s[..]).rfind(|n| ["+mte", "-mte"].contains(&&n[..]));
if let None | Some("-mte") = mte_feature {
cx.tcx.sess.err("`-Zsanitizer=memtag` requires `-Ctarget-feature=+mte`");
}
attrs.push(llvm::AttributeKind::SanitizeMemTag.create_attr(cx.llcx));
@ -382,10 +380,7 @@ pub fn from_fn_attrs<'ll, 'tcx>(
let mut function_features = function_features
.iter()
.flat_map(|feat| {
llvm_util::to_llvm_feature(cx.tcx.sess, feat)
.into_iter()
.map(|f| format!("+{}", f))
.collect::<Vec<String>>()
llvm_util::to_llvm_features(cx.tcx.sess, feat).into_iter().map(|f| format!("+{}", f))
})
.chain(codegen_fn_attrs.instruction_set.iter().map(|x| match x {
InstructionSetAttr::ArmA32 => "-thumb-mode".to_string(),
@ -418,10 +413,11 @@ pub fn from_fn_attrs<'ll, 'tcx>(
}
if !function_features.is_empty() {
let mut global_features = llvm_util::llvm_global_features(cx.tcx.sess);
global_features.extend(function_features.into_iter());
let features = global_features.join(",");
let val = CString::new(features).unwrap();
let global_features = cx.tcx.global_backend_features(()).iter().map(|s| &s[..]);
let val = global_features
.chain(function_features.iter().map(|s| &s[..]))
.intersperse(",")
.collect::<SmallCStr>();
to_add.push(llvm::CreateAttrStringValue(cx.llcx, cstr!("target-features"), &val));
}

17
compiler/rustc_codegen_llvm/src/back/write.rs
View file

@ -100,7 +100,10 @@ pub fn write_output_file<'ll>(
pub fn create_informational_target_machine(sess: &Session) -> &'static mut llvm::TargetMachine {
let config = TargetMachineFactoryConfig { split_dwarf_file: None };
target_machine_factory(sess, config::OptLevel::No)(config)
// Can't use query system here quite yet because this function is invoked before the query
// system/tcx is set up.
let features = llvm_util::global_llvm_features(sess, false);
target_machine_factory(sess, config::OptLevel::No, &features)(config)
.unwrap_or_else(|err| llvm_err(sess.diagnostic(), &err).raise())
}
@ -115,8 +118,12 @@ pub fn create_target_machine(tcx: TyCtxt<'_>, mod_name: &str) -> &'static mut ll
None
};
let config = TargetMachineFactoryConfig { split_dwarf_file };
target_machine_factory(tcx.sess, tcx.backend_optimization_level(()))(config)
.unwrap_or_else(|err| llvm_err(tcx.sess.diagnostic(), &err).raise())
target_machine_factory(
&tcx.sess,
tcx.backend_optimization_level(()),
tcx.global_backend_features(()),
)(config)
.unwrap_or_else(|err| llvm_err(tcx.sess.diagnostic(), &err).raise())
}
pub fn to_llvm_opt_settings(
@ -171,6 +178,7 @@ pub(crate) fn to_llvm_code_model(code_model: Option<CodeModel>) -> llvm::CodeMod
pub fn target_machine_factory(
sess: &Session,
optlvl: config::OptLevel,
target_features: &[String],
) -> TargetMachineFactoryFn<LlvmCodegenBackend> {
let reloc_model = to_llvm_relocation_model(sess.relocation_model());
@ -195,8 +203,7 @@ pub fn target_machine_factory(
let triple = SmallCStr::new(&sess.target.llvm_target);
let cpu = SmallCStr::new(llvm_util::target_cpu(sess));
let features = llvm_util::llvm_global_features(sess).join(",");
let features = CString::new(features).unwrap();
let features = CString::new(target_features.join(",")).unwrap();
let abi = SmallCStr::new(&sess.target.llvm_abiname);
let trap_unreachable =
sess.opts.debugging_opts.trap_unreachable.unwrap_or(sess.target.trap_unreachable);

10
compiler/rustc_codegen_llvm/src/lib.rs
View file

@ -11,6 +11,7 @@
#![feature(extern_types)]
#![feature(once_cell)]
#![feature(nll)]
#![feature(iter_intersperse)]
#![recursion_limit = "256"]
#![allow(rustc::potential_query_instability)]
@ -32,6 +33,7 @@ use rustc_data_structures::fx::FxHashMap;
use rustc_errors::{ErrorReported, FatalError, Handler};
use rustc_metadata::EncodedMetadata;
use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
use rustc_middle::ty::query::Providers;
use rustc_middle::ty::TyCtxt;
use rustc_session::config::{OptLevel, OutputFilenames, PrintRequest};
use rustc_session::Session;
@ -126,8 +128,9 @@ impl ExtraBackendMethods for LlvmCodegenBackend {
&self,
sess: &Session,
optlvl: OptLevel,
target_features: &[String],
) -> TargetMachineFactoryFn<Self> {
back::write::target_machine_factory(sess, optlvl)
back::write::target_machine_factory(sess, optlvl, target_features)
}
fn target_cpu<'b>(&self, sess: &'b Session) -> &'b str {
llvm_util::target_cpu(sess)
@ -251,6 +254,11 @@ impl CodegenBackend for LlvmCodegenBackend {
llvm_util::init(sess); // Make sure llvm is inited
}
fn provide(&self, providers: &mut Providers) {
providers.global_backend_features =
|tcx, ()| llvm_util::global_llvm_features(tcx.sess, true)
}
fn print(&self, req: PrintRequest, sess: &Session) {
match req {
PrintRequest::RelocationModels => {

198
compiler/rustc_codegen_llvm/src/llvm_util.rs
View file

@ -2,14 +2,18 @@ use crate::back::write::create_informational_target_machine;
use crate::{llvm, llvm_util};
use libc::c_int;
use libloading::Library;
use rustc_codegen_ssa::target_features::{supported_target_features, tied_target_features};
use rustc_codegen_ssa::target_features::{
supported_target_features, tied_target_features, RUSTC_SPECIFIC_FEATURES,
};
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_data_structures::small_c_str::SmallCStr;
use rustc_fs_util::path_to_c_string;
use rustc_middle::bug;
use rustc_session::config::PrintRequest;
use rustc_session::Session;
use rustc_span::symbol::Symbol;
use rustc_target::spec::{MergeFunctions, PanicStrategy};
use smallvec::{smallvec, SmallVec};
use std::ffi::{CStr, CString};
use tracing::debug;
@ -155,9 +159,10 @@ pub fn time_trace_profiler_finish(file_name: &Path) {
}
}
// WARNING: the features after applying `to_llvm_feature` must be known
// WARNING: the features after applying `to_llvm_features` must be known
// to LLVM or the feature detection code will walk past the end of the feature
// array, leading to crashes.
//
// To find a list of LLVM's names, check llvm-project/llvm/include/llvm/Support/*TargetParser.def
// where the * matches the architecture's name
// Beware to not use the llvm github project for this, but check the git submodule
@ -165,35 +170,35 @@ pub fn time_trace_profiler_finish(file_name: &Path) {
// Though note that Rust can also be build with an external precompiled version of LLVM
// which might lead to failures if the oldest tested / supported LLVM version
// doesn't yet support the relevant intrinsics
pub fn to_llvm_feature<'a>(sess: &Session, s: &'a str) -> Vec<&'a str> {
pub fn to_llvm_features<'a>(sess: &Session, s: &'a str) -> SmallVec<[&'a str; 2]> {
let arch = if sess.target.arch == "x86_64" { "x86" } else { &*sess.target.arch };
match (arch, s) {
("x86", "sse4.2") => {
if get_version() >= (14, 0, 0) {
vec!["sse4.2", "crc32"]
smallvec!["sse4.2", "crc32"]
} else {
vec!["sse4.2"]
smallvec!["sse4.2"]
}
}
("x86", "pclmulqdq") => vec!["pclmul"],
("x86", "rdrand") => vec!["rdrnd"],
("x86", "bmi1") => vec!["bmi"],
("x86", "cmpxchg16b") => vec!["cx16"],
("x86", "avx512vaes") => vec!["vaes"],
("x86", "avx512gfni") => vec!["gfni"],
("x86", "avx512vpclmulqdq") => vec!["vpclmulqdq"],
("aarch64", "fp") => vec!["fp-armv8"],
("aarch64", "fp16") => vec!["fullfp16"],
("aarch64", "fhm") => vec!["fp16fml"],
("aarch64", "rcpc2") => vec!["rcpc-immo"],
("aarch64", "dpb") => vec!["ccpp"],
("aarch64", "dpb2") => vec!["ccdp"],
("aarch64", "frintts") => vec!["fptoint"],
("aarch64", "fcma") => vec!["complxnum"],
("aarch64", "pmuv3") => vec!["perfmon"],
("aarch64", "paca") => vec!["pauth"],
("aarch64", "pacg") => vec!["pauth"],
(_, s) => vec![s],
("x86", "pclmulqdq") => smallvec!["pclmul"],
("x86", "rdrand") => smallvec!["rdrnd"],
("x86", "bmi1") => smallvec!["bmi"],
("x86", "cmpxchg16b") => smallvec!["cx16"],
("x86", "avx512vaes") => smallvec!["vaes"],
("x86", "avx512gfni") => smallvec!["gfni"],
("x86", "avx512vpclmulqdq") => smallvec!["vpclmulqdq"],
("aarch64", "fp") => smallvec!["fp-armv8"],
("aarch64", "fp16") => smallvec!["fullfp16"],
("aarch64", "fhm") => smallvec!["fp16fml"],
("aarch64", "rcpc2") => smallvec!["rcpc-immo"],
("aarch64", "dpb") => smallvec!["ccpp"],
("aarch64", "dpb2") => smallvec!["ccdp"],
("aarch64", "frintts") => smallvec!["fptoint"],
("aarch64", "fcma") => smallvec!["complxnum"],
("aarch64", "pmuv3") => smallvec!["perfmon"],
("aarch64", "paca") => smallvec!["pauth"],
("aarch64", "pacg") => smallvec!["pauth"],
(_, s) => smallvec![s],
}
}
@ -207,7 +212,6 @@ pub fn check_tied_features(
// Tied features must be set to the same value, or not set at all
let mut tied_iter = tied.iter();
let enabled = features.get(tied_iter.next().unwrap());
if tied_iter.any(|f| enabled != features.get(f)) {
return Some(tied);
}
@ -224,8 +228,8 @@ pub fn target_features(sess: &Session) -> Vec<Symbol> {
if sess.is_nightly_build() || gate.is_none() { Some(feature) } else { None }
})
.filter(|feature| {
for llvm_feature in to_llvm_feature(sess, feature) {
let cstr = CString::new(llvm_feature).unwrap();
for llvm_feature in to_llvm_features(sess, feature) {
let cstr = SmallCStr::new(llvm_feature);
if unsafe { llvm::LLVMRustHasFeature(target_machine, cstr.as_ptr()) } {
return true;
}
@ -292,9 +296,9 @@ fn print_target_features(sess: &Session, tm: &llvm::TargetMachine) {
let mut rustc_target_features = supported_target_features(sess)
.iter()
.filter_map(|(feature, _gate)| {
for llvm_feature in to_llvm_feature(sess, *feature) {
for llvm_feature in to_llvm_features(sess, *feature) {
// LLVM asserts that these are sorted. LLVM and Rust both use byte comparison for these strings.
match target_features.binary_search_by_key(&llvm_feature, |(f, _d)| (*f)).ok().map(
match target_features.binary_search_by_key(&llvm_feature, |(f, _d)| f).ok().map(
|index| {
let (_f, desc) = target_features.remove(index);
(*feature, desc)
@ -364,14 +368,7 @@ pub fn target_cpu(sess: &Session) -> &str {
/// The list of LLVM features computed from CLI flags (`-Ctarget-cpu`, `-Ctarget-feature`,
/// `--target` and similar).
// FIXME(nagisa): Cache the output of this somehow? Maybe make this a query? We're calling this
// for every function that has `#[target_feature]` on it. The global features won't change between
// the functions; only crates, maybe…
pub fn llvm_global_features(sess: &Session) -> Vec<String> {
// FIXME(nagisa): this should definitely be available more centrally and to other codegen backends.
/// These features control behaviour of rustc rather than llvm.
const RUSTC_SPECIFIC_FEATURES: &[&str] = &["crt-static"];
pub(crate) fn global_llvm_features(sess: &Session, diagnostics: bool) -> Vec<String> {
// Features that come earlier are overriden by conflicting features later in the string.
// Typically we'll want more explicit settings to override the implicit ones, so:
//
@ -417,49 +414,110 @@ pub fn llvm_global_features(sess: &Session) -> Vec<String> {
Some(_) | None => {}
};
fn strip(s: &str) -> &str {
s.strip_prefix(&['+', '-']).unwrap_or(s)
// Features implied by an implicit or explicit `--target`.
features.extend(
sess.target
.features
.split(',')
.filter(|v| !v.is_empty() && backend_feature_name(v).is_some())
.map(String::from),
);
// -Ctarget-features
let supported_features = supported_target_features(sess);
let feats = sess
.opts
.cg
.target_feature
.split(',')
.filter_map(|s| {
let enable_disable = match s.chars().next() {
None => return None,
Some(c @ '+' | c @ '-') => c,
Some(_) => {
if diagnostics {
let mut diag = sess.struct_warn(&format!(
"unknown feature specified for `-Ctarget-feature`: `{}`",
s
));
diag.note("features must begin with a `+` to enable or `-` to disable it");
diag.emit();
}
return None;
}
};
let feature = backend_feature_name(s)?;
// Warn against use of LLVM specific feature names on the CLI.
if diagnostics && !supported_features.iter().any(|&(v, _)| v == feature) {
let rust_feature = supported_features.iter().find_map(|&(rust_feature, _)| {
let llvm_features = to_llvm_features(sess, rust_feature);
if llvm_features.contains(&feature) && !llvm_features.contains(&rust_feature) {
Some(rust_feature)
} else {
None
}
});
let mut diag = sess.struct_warn(&format!(
"unknown feature specified for `-Ctarget-feature`: `{}`",
feature
));
diag.note("it is still passed through to the codegen backend");
if let Some(rust_feature) = rust_feature {
diag.help(&format!("you might have meant: `{}`", rust_feature));
} else {
diag.note("consider filing a feature request");
}
diag.emit();
}
Some((enable_disable, feature))
})
.collect::<SmallVec<[(char, &str); 8]>>();
if diagnostics {
// FIXME(nagisa): figure out how to not allocate a full hashset here.
let featmap = feats.iter().map(|&(flag, feat)| (feat, flag == '+')).collect();
if let Some(f) = check_tied_features(sess, &featmap) {
sess.err(&format!(
"target features {} must all be enabled or disabled together",
f.join(", ")
));
}
}
let filter = |s: &str| {
if s.is_empty() {
return vec![];
}
let feature = strip(s);
if feature == s {
return vec![s.to_string()];
}
// Rustc-specific feature requests like `+crt-static` or `-crt-static`
// are not passed down to LLVM.
features.extend(feats.into_iter().flat_map(|(enable_disable, feature)| {
// rustc-specific features do not get passed down to LLVM…
if RUSTC_SPECIFIC_FEATURES.contains(&feature) {
return vec![];
return SmallVec::<[_; 2]>::new();
}
// ... otherwise though we run through `to_llvm_feature` feature when
// ... otherwise though we run through `to_llvm_feature when
// passing requests down to LLVM. This means that all in-language
// features also work on the command line instead of having two
// different names when the LLVM name and the Rust name differ.
to_llvm_feature(sess, feature).iter().map(|f| format!("{}{}", &s[..1], f)).collect()
};
// Features implied by an implicit or explicit `--target`.
features.extend(sess.target.features.split(',').flat_map(&filter));
// -Ctarget-features
let feats: Vec<&str> = sess.opts.cg.target_feature.split(',').collect();
// LLVM enables based on the last occurence of a feature
if let Some(f) =
check_tied_features(sess, &feats.iter().map(|f| (strip(f), !f.starts_with("-"))).collect())
{
sess.err(&format!(
"Target features {} must all be enabled or disabled together",
f.join(", ")
));
}
features.extend(feats.iter().flat_map(|&f| filter(f)));
to_llvm_features(sess, feature)
.into_iter()
.map(|f| format!("{}{}", enable_disable, f))
.collect()
}));
features
}
/// Returns a feature name for the given `+feature` or `-feature` string.
///
/// Only allows features that are backend specific (i.e. not [`RUSTC_SPECIFIC_FEATURES`].)
fn backend_feature_name(s: &str) -> Option<&str> {
// features must start with a `+` or `-`.
let feature = s.strip_prefix(&['+', '-'][..]).unwrap_or_else(|| {
bug!("target feature `{}` must begin with a `+` or `-`", s);
});
// Rustc-specific feature requests like `+crt-static` or `-crt-static`
// are not passed down to LLVM.
if RUSTC_SPECIFIC_FEATURES.contains(&feature) {
return None;
}
Some(feature)
}
pub fn tune_cpu(sess: &Session) -> Option<&str> {
let name = sess.opts.debugging_opts.tune_cpu.as_ref()?;
Some(handle_native(name))