Auto merge of #61268 - michaelwoerister:stabilize-pgo, r=alexcrichton

Stabilize support for Profile-guided Optimization

This PR makes profile-guided optimization available via the `-C profile-generate` / `-C profile-use` pair of commandline flags and adds end-user documentation for the feature to the [rustc book](https://doc.rust-lang.org/rustc/). The PR thus ticks the last two remaining checkboxes of the [stabilization tracking issue](https://github.com/rust-lang/rust/issues/59913).

From the tracking issue:
> Profile-guided optimization (PGO) is a common optimization technique for ahead-of-time compilers. It works by collecting data about a program's typical execution (e.g. probability of branches taken, typical runtime values of variables, etc) and then uses this information during program optimization for things like inlining decisions, machine code layout, or indirect call promotion.

If you are curious about how this can be used, there is a rendered version of the documentation this PR adds available [here](
https://github.com/michaelwoerister/rust/blob/stabilize-pgo/src/doc/rustc/src/profile-guided-optimization.md).

r? @alexcrichton
cc @rust-lang/compiler

3 files changed, 4 insertions, 4 deletions

diff --git a/src/librustc_codegen_ssa/back/link.rs b/src/librustc_codegen_ssa/back/link.rs
index 618e8b8699f..e3d297e7862 100644
--- a/src/librustc_codegen_ssa/back/link.rs
+++ b/src/librustc_codegen_ssa/back/link.rs
@@ -1179,7 +1179,7 @@ fn link_args<'a, B: ArchiveBuilder<'a>>(cmd: &mut dyn Linker,
         cmd.build_static_executable();
     }
 
-    if sess.opts.debugging_opts.pgo_gen.enabled() {
+    if sess.opts.cg.profile_generate.enabled() {
         cmd.pgo_gen();
     }
 
diff --git a/src/librustc_codegen_ssa/back/symbol_export.rs b/src/librustc_codegen_ssa/back/symbol_export.rs
index b9ee82f108a..3e0f030527f 100644
--- a/src/librustc_codegen_ssa/back/symbol_export.rs
+++ b/src/librustc_codegen_ssa/back/symbol_export.rs
@@ -203,7 +203,7 @@ fn exported_symbols_provider_local<'tcx>(
         }
     }
 
-    if tcx.sess.opts.debugging_opts.pgo_gen.enabled() {
+    if tcx.sess.opts.cg.profile_generate.enabled() {
         // These are weak symbols that point to the profile version and the
         // profile name, which need to be treated as exported so LTO doesn't nix
         // them.
diff --git a/src/librustc_codegen_ssa/back/write.rs b/src/librustc_codegen_ssa/back/write.rs
index 309187ca2ea..6364843d772 100644
--- a/src/librustc_codegen_ssa/back/write.rs
+++ b/src/librustc_codegen_ssa/back/write.rs
@@ -423,8 +423,8 @@ pub fn start_async_codegen<B: ExtraBackendMethods>(
         modules_config.passes.push("insert-gcov-profiling".to_owned())
     }
 
-    modules_config.pgo_gen = sess.opts.debugging_opts.pgo_gen.clone();
-    modules_config.pgo_use = sess.opts.debugging_opts.pgo_use.clone();
+    modules_config.pgo_gen = sess.opts.cg.profile_generate.clone();
+    modules_config.pgo_use = sess.opts.cg.profile_use.clone();
 
     modules_config.opt_level = Some(sess.opts.optimize);
     modules_config.opt_size = Some(sess.opts.optimize);