Auto merge of #83666 - Amanieu:instrprof-order, r=tmandry

Run LLVM coverage instrumentation passes before optimization passes

This matches the behavior of Clang and allows us to remove several
hacks which were needed to ensure functions weren't optimized away
before reaching the instrumentation pass.

Fixes #83429

cc `@richkadel`

r? `@tmandry`

compiler/rustc_mir/src/monomorphize/partitioning/mod.rs

@@ -196,13 +196,7 @@ pub fn partition<'tcx>(
 
     // Next we try to make as many symbols "internal" as possible, so LLVM has
     // more freedom to optimize.
-    if !tcx.sess.link_dead_code() && !tcx.sess.instrument_coverage() {
-        // Disabled for `-Z instrument-coverage` because some LLVM optimizations can sometimes
-        // break coverage results. Tests that failed at certain optimization levels are now
-        // validated at those optimization levels (via `compile-flags` directive); for example:
-        //   * `src/test/run-make-fulldeps/coverage/async.rs` broke with `-C opt-level=1`
-        //   * `src/test/run-make-fulldeps/coverage/closure.rs` broke with `-C opt-level=2`, and
-        //     also required disabling `generate_gcu_internal_copies` in `rustc_middle/mir/mono.rs`
+    if !tcx.sess.link_dead_code() {
         let _prof_timer = tcx.prof.generic_activity("cgu_partitioning_internalize_symbols");
         partitioner.internalize_symbols(cx, &mut post_inlining);
     }