Rollup merge of rust-lang#78873 - tmiasko:inline-opts, r=oli-obk

Add flags customizing behaviour of MIR inlining

* `-Zinline-mir-threshold` to change the default threshold.
* `-Zinline-mir-hint-threshold` to change the threshold used by
  functions with inline hint.

Having those as configurable flags makes it possible to experiment with with
different inlining thresholds and substantially increase test coverage of MIR
inlining when used with increased thresholds (for example, necessary to test
rust-lang#78844).

Author: jonas-schievink

compiler/rustc_interface/src/tests.rs

@@ -554,6 +554,8 @@ fn test_debugging_options_tracking_hash() {
     tracked!(function_sections, Some(false));
     tracked!(human_readable_cgu_names, true);
     tracked!(inline_in_all_cgus, Some(true));
+    tracked!(inline_mir_threshold, 123);
+    tracked!(inline_mir_hint_threshold, 123);
     tracked!(insert_sideeffect, true);
     tracked!(instrument_coverage, true);
     tracked!(instrument_mcount, true);

compiler/rustc_mir/src/transform/inline.rs

@@ -16,9 +16,6 @@ use crate::transform::MirPass;
 use std::iter;
 use std::ops::{Range, RangeFrom};
 
-const DEFAULT_THRESHOLD: usize = 50;
-const HINT_THRESHOLD: usize = 100;
-
 const INSTR_COST: usize = 5;
 const CALL_PENALTY: usize = 25;
 const LANDINGPAD_PENALTY: usize = 50;
@@ -248,7 +245,11 @@ impl Inliner<'tcx> {
             }
         }
 
-        let mut threshold = if hinted { HINT_THRESHOLD } else { DEFAULT_THRESHOLD };
+        let mut threshold = if hinted {
+            self.tcx.sess.opts.debugging_opts.inline_mir_hint_threshold
+        } else {
+            self.tcx.sess.opts.debugging_opts.inline_mir_threshold
+        };
 
         // Significantly lower the threshold for inlining cold functions
         if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::COLD) {

compiler/rustc_session/src/options.rs

@@ -929,6 +929,10 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         (default: no)"),
     incremental_verify_ich: bool = (false, parse_bool, [UNTRACKED],
         "verify incr. comp. hashes of green query instances (default: no)"),
+    inline_mir_threshold: usize = (50, parse_uint, [TRACKED],
+        "a default MIR inlining threshold (default: 50)"),
+    inline_mir_hint_threshold: usize = (100, parse_uint, [TRACKED],
+        "inlining threshold for functions with inline hint (default: 100)"),
     inline_in_all_cgus: Option<bool> = (None, parse_opt_bool, [TRACKED],
         "control whether `#[inline]` functions are in all CGUs"),
     input_stats: bool = (false, parse_bool, [UNTRACKED],

src/test/mir-opt/inline/inline-options.rs

@@ -0,0 +1,19 @@
+// Checks that inlining threshold can be controlled with
+// inline-mir-threshold and inline-hint-threshold options.
+//
+// compile-flags: -Zinline-mir-threshold=90
+// compile-flags: -Zinline-mir-hint-threshold=50
+
+// EMIT_MIR inline_options.main.Inline.after.mir
+fn main() {
+    not_inlined();
+    inlined::<u32>();
+}
+
+// Cost is approximately 3 * 25 + 5 = 80.
+#[inline]
+pub fn not_inlined() { g(); g(); g(); }
+pub fn inlined<T>() { g(); g(); g(); }
+
+#[inline(never)]
+fn g() {}

src/test/mir-opt/inline/inline_options.main.Inline.after.mir

@@ -0,0 +1,56 @@
+// MIR for `main` after Inline
+
+fn main() -> () {
+    let mut _0: ();                      // return place in scope 0 at $DIR/inline-options.rs:8:11: 8:11
+    let _1: ();                          // in scope 0 at $DIR/inline-options.rs:9:5: 9:18
+    let _2: ();                          // in scope 0 at $DIR/inline-options.rs:10:5: 10:21
+    scope 1 (inlined inlined::<u32>) {   // at $DIR/inline-options.rs:10:5: 10:21
+        let _3: ();                      // in scope 1 at $DIR/inline-options.rs:10:5: 10:21
+        let _4: ();                      // in scope 1 at $DIR/inline-options.rs:10:5: 10:21
+        let _5: ();                      // in scope 1 at $DIR/inline-options.rs:10:5: 10:21
+    }
+
+    bb0: {
+        StorageLive(_1);                 // scope 0 at $DIR/inline-options.rs:9:5: 9:18
+        _1 = not_inlined() -> bb1;       // scope 0 at $DIR/inline-options.rs:9:5: 9:18
+                                         // mir::Constant
+                                         // + span: $DIR/inline-options.rs:9:5: 9:16
+                                         // + literal: Const { ty: fn() {not_inlined}, val: Value(Scalar(<ZST>)) }
+    }
+
+    bb1: {
+        StorageDead(_1);                 // scope 0 at $DIR/inline-options.rs:9:18: 9:19
+        StorageLive(_2);                 // scope 0 at $DIR/inline-options.rs:10:5: 10:21
+        StorageLive(_3);                 // scope 1 at $DIR/inline-options.rs:10:5: 10:21
+        _3 = g() -> bb2;                 // scope 1 at $DIR/inline-options.rs:10:5: 10:21
+                                         // mir::Constant
+                                         // + span: $DIR/inline-options.rs:10:5: 10:21
+                                         // + literal: Const { ty: fn() {g}, val: Value(Scalar(<ZST>)) }
+    }
+
+    bb2: {
+        StorageDead(_3);                 // scope 1 at $DIR/inline-options.rs:10:5: 10:21
+        StorageLive(_4);                 // scope 1 at $DIR/inline-options.rs:10:5: 10:21
+        _4 = g() -> bb3;                 // scope 1 at $DIR/inline-options.rs:10:5: 10:21
+                                         // mir::Constant
+                                         // + span: $DIR/inline-options.rs:10:5: 10:21
+                                         // + literal: Const { ty: fn() {g}, val: Value(Scalar(<ZST>)) }
+    }
+
+    bb3: {
+        StorageDead(_4);                 // scope 1 at $DIR/inline-options.rs:10:5: 10:21
+        StorageLive(_5);                 // scope 1 at $DIR/inline-options.rs:10:5: 10:21
+        _5 = g() -> bb4;                 // scope 1 at $DIR/inline-options.rs:10:5: 10:21
+                                         // mir::Constant
+                                         // + span: $DIR/inline-options.rs:10:5: 10:21
+                                         // + literal: Const { ty: fn() {g}, val: Value(Scalar(<ZST>)) }
+    }
+
+    bb4: {
+        StorageDead(_5);                 // scope 1 at $DIR/inline-options.rs:10:5: 10:21
+        _2 = const ();                   // scope 1 at $DIR/inline-options.rs:10:5: 10:21
+        StorageDead(_2);                 // scope 0 at $DIR/inline-options.rs:10:21: 10:22
+        _0 = const ();                   // scope 0 at $DIR/inline-options.rs:8:11: 11:2
+        return;                          // scope 0 at $DIR/inline-options.rs:11:2: 11:2
+    }
+}