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Merged
rust-bors merged 9 commits into from
Aug 17, 2026
Merged

Stabilize -Zprofile-sample-use #155942

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f6ee72b
doc: update PGO guide with Sample-based PGO information
Apr 28, 2026
84f2d63
doc: move option description from Unstable book to the proper place
Apr 28, 2026
9c33952
fix: make stabilization preparation for the flags
Apr 28, 2026
6978fab
doc: a attempt to add PGO-related UI tests
May 10, 2026
f19a92f
doc: add more information about the flags
zamazan4ik May 31, 2026
4cc83fd
doc: apply 80 width limit to the PGO guide
May 31, 2026
167a496
doc: add more information about debuginfo-for-profiling
May 31, 2026
0570f86
fix: remove debuginfo-for-profiling from stabilization
Jun 1, 2026
01a5987
doc: add a small note about unstable flag
zamazan4ik Jun 2, 2026
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2 changes: 1 addition & 1 deletion compiler/rustc_codegen_llvm/src/attributes.rs
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Expand Up @@ -435,7 +435,7 @@ pub(crate) fn llfn_attrs_from_instance<'ll, 'tcx>(
to_add.push(uwtable_attr(cx.llcx, sess.opts.unstable_opts.use_sync_unwind));
}

if sess.opts.unstable_opts.profile_sample_use.is_some() {
if sess.opts.cg.profile_sample_use.is_some() {
to_add.push(llvm::CreateAttrString(cx.llcx, "use-sample-profile"));
}

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2 changes: 1 addition & 1 deletion compiler/rustc_codegen_ssa/src/back/linker.rs
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Expand Up @@ -422,7 +422,7 @@ impl<'a> GccLinker<'a> {
config::OptLevel::Aggressive => "O3",
};

if let Some(path) = &self.sess.opts.unstable_opts.profile_sample_use {
if let Some(path) = &self.sess.opts.cg.profile_sample_use {
self.link_arg(&format!("-plugin-opt=sample-profile={}", path.display()));
};
let prefix = if self.codegen_backend == "gcc" {
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2 changes: 1 addition & 1 deletion compiler/rustc_codegen_ssa/src/back/write.rs
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Expand Up @@ -179,7 +179,7 @@ impl ModuleConfig {
SwitchWithOptPath::Disabled
),
pgo_use: if_regular!(sess.opts.cg.profile_use.clone(), None),
pgo_sample_use: if_regular!(sess.opts.unstable_opts.profile_sample_use.clone(), None),
pgo_sample_use: if_regular!(sess.opts.cg.profile_sample_use.clone(), None),
debug_info_for_profiling: sess.opts.unstable_opts.debuginfo_for_profiling,
instrument_coverage: if_regular!(sess.instrument_coverage(), false),

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2 changes: 1 addition & 1 deletion compiler/rustc_interface/src/passes.rs
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Expand Up @@ -651,7 +651,7 @@ fn write_out_deps(tcx: TyCtxt<'_>, outputs: &OutputFilenames, out_filenames: &[P
checksum_hash_algo,
));
}
if let Some(ref profile_sample) = sess.opts.unstable_opts.profile_sample_use {
if let Some(ref profile_sample) = sess.opts.cg.profile_sample_use {
files.extend(hash_iter_files(
iter::once(normalize_path(profile_sample.as_path().to_path_buf())),
checksum_hash_algo,
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2 changes: 1 addition & 1 deletion compiler/rustc_interface/src/tests.rs
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Expand Up @@ -631,6 +631,7 @@ fn test_codegen_options_tracking_hash() {
tracked!(passes, vec![String::from("1"), String::from("2")]);
tracked!(prefer_dynamic, true);
tracked!(profile_generate, SwitchWithOptPath::Enabled(None));
tracked!(profile_sample_use, Some(PathBuf::from("abc")));
tracked!(profile_use, Some(PathBuf::from("abc")));
tracked!(relocation_model, Some(RelocModel::Pic));
tracked!(relro_level, Some(RelroLevel::Full));
Expand Down Expand Up @@ -845,7 +846,6 @@ fn test_unstable_options_tracking_hash() {
tracked!(plt, Some(true));
tracked!(polonius, Polonius::Legacy);
tracked!(precise_enum_drop_elaboration, false);
tracked!(profile_sample_use, Some(PathBuf::from("abc")));
tracked!(profiler_runtime, "abc".to_string());
tracked!(reg_struct_return, true);
tracked!(regparm, Some(3));
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4 changes: 2 additions & 2 deletions compiler/rustc_session/src/config.rs
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Expand Up @@ -2489,11 +2489,11 @@ pub fn build_session_options(early_dcx: &mut EarlyDiagCtxt, matches: &getopts::M
early_dcx.early_fatal("options `-C profile-generate` and `-C profile-use` are exclusive");
}

if unstable_opts.profile_sample_use.is_some()
if cg.profile_sample_use.is_some()
&& (cg.profile_generate.enabled() || cg.profile_use.is_some())
{
early_dcx.early_fatal(
"option `-Z profile-sample-use` cannot be used with `-C profile-generate` or `-C profile-use`",
"option `-C profile-sample-use` cannot be used with `-C profile-generate` or `-C profile-use`",
);
}

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6 changes: 3 additions & 3 deletions compiler/rustc_session/src/options.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2139,6 +2139,8 @@ options! {
profile_generate: SwitchWithOptPath = (SwitchWithOptPath::Disabled,
parse_switch_with_opt_path, [TRACKED],
"compile the program with profiling instrumentation"),
profile_sample_use: Option<PathBuf> = (None, parse_opt_pathbuf, [TRACKED],
"use the given `.prof` file for sample-based profile-guided optimization"),
profile_use: Option<PathBuf> = (None, parse_opt_pathbuf, [TRACKED],
"use the given `.profdata` file for profile-guided optimization"),
#[rustc_lint_opt_deny_field_access("use `Session::relocation_model` instead of this field")]
Expand Down Expand Up @@ -2257,7 +2259,7 @@ options! {
debuginfo_compression: DebugInfoCompression = (DebugInfoCompression::None, parse_debuginfo_compression, [TRACKED],
"compress debug info sections (none, zlib, zstd, default: none)"),
debuginfo_for_profiling: bool = (false, parse_bool, [TRACKED],
"emit discriminators and other data necessary for AutoFDO"),
"emit extra debug info to make sample profile more accurate"),

@folkertdev folkertdev Aug 16, 2026

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This isn't really part of the stabilization. Both the old and new descriptions are kind of vague to me. Do you still want to keep the updated text? (fine by me if so)

@zamazan4ik zamazan4ik Aug 16, 2026

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Yeah, I would like to keep this small update in this PR even if it's not directly related for the stabilization. By this change, I wanted to keep the flag description in sync with the same flag for Clang - https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-fdebug-info-for-profiling . Since PGO (and especially Sampling PGO) coverage across the ecosystem is really small, I wanted to reduce any kind of difference between two compilers in a place where they describe the same thing - so less potential questions would be raised by people in the future.

Please don't get me wrong - I am also not that happy with this explanation. But I think it's better than we had before. I hope in the future we will try to get rid of this flag completely (and integrate into some debuginfo level by default, as was previously lightly discussed somewhere in Zulip) but it's not yet done.

deduplicate_diagnostics: bool = (true, parse_bool, [UNTRACKED],
"deduplicate identical diagnostics (default: yes)"),
default_visibility: Option<SymbolVisibility> = (None, parse_opt_symbol_visibility, [TRACKED],
Expand Down Expand Up @@ -2562,8 +2564,6 @@ options! {
"how to run proc-macro code (default: same-thread)"),
profile_closures: bool = (false, parse_no_value, [UNTRACKED],
"profile size of closures"),
profile_sample_use: Option<PathBuf> = (None, parse_opt_pathbuf, [TRACKED],
"use the given `.prof` file for sampled profile-guided optimization (also known as AutoFDO)"),
profiler_runtime: String = (String::from("profiler_builtins"), parse_string, [TRACKED],
"name of the profiler runtime crate to automatically inject (default: `profiler_builtins`)"),
query_dep_graph: bool = (false, parse_bool, [UNTRACKED],
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_session/src/session.rs
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Expand Up @@ -1168,7 +1168,7 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
}

// Do the same for sample profile data.
if let Some(ref path) = sess.opts.unstable_opts.profile_sample_use {
if let Some(ref path) = sess.opts.cg.profile_sample_use {
if !path.exists() {
sess.dcx().emit_err(errors::ProfileSampleUseFileDoesNotExist { path });
}
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9 changes: 9 additions & 0 deletions src/doc/rustc/src/codegen-options/index.md
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Expand Up @@ -525,6 +525,15 @@ an optional argument which is the path to a directory into which the
instrumented binary will emit the collected data. See the chapter on
[profile-guided optimization] for more information.

## profile-sample-use

This flag specifies the profiling data file to be used for sample-based
profile-guided optimization (SPGO). The flag takes a mandatory argument which
is the path to a valid `.prof` file. See the chapter on
[profile-guided optimization] for more information.
The `-Zdebuginfo-for-profiling` can be used to improve the quality of the
profiling data.

## profile-use

This flag specifies the profiling data file to be used for profile-guided
Expand Down
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