Rollup merge of rust-lang#76899 - wesleywiser:experimental_unsound_mi…

…r_opts_flag, r=oli-obk

[mir-opt] Introduce a new flag to enable experimental/unsound mir opts

This implements part of rust-lang/compiler-team#319. The exact name of this flag was not decided as part of that MCP and some people expressed that it should include "unsound" in some way.

I've chosen to use `enable-experimental-unsound-mir-opts` as the name. While long, I don't think that matters too much as really it will only be used by some mir-opt tests. If you object or have a better name, please leave a comment!

r? @oli-obk
cc @rust-lang/wg-mir-opt @RalfJung

compiler/rustc_mir/src/transform/copy_prop.rs

@@ -31,9 +31,11 @@ pub struct CopyPropagation;
 
 impl<'tcx> MirPass<'tcx> for CopyPropagation {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, _source: MirSource<'tcx>, body: &mut Body<'tcx>) {
+        let opts = &tcx.sess.opts.debugging_opts;
         // We only run when the MIR optimization level is > 1.
         // This avoids a slow pass, and messing up debug info.
-        if tcx.sess.opts.debugging_opts.mir_opt_level <= 1 {
+        // FIXME(76740): This optimization is buggy and can cause unsoundness.
+        if opts.mir_opt_level <= 1 || !opts.unsound_mir_opts {
             return;
         }
 

compiler/rustc_mir/src/transform/simplify_try.rs

@@ -612,7 +612,7 @@ impl<'a, 'tcx> SimplifyBranchSameOptimizationFinder<'a, 'tcx> {
                     && bb_l.terminator().kind == bb_r.terminator().kind;
                     let statement_check = || {
                         bb_l.statements.iter().zip(&bb_r.statements).try_fold(StatementEquality::TrivialEqual, |acc,(l,r)| {
-                            let stmt_equality = self.statement_equality(*adt_matched_on, &l, bb_l_idx, &r, bb_r_idx, self.tcx.sess.opts.debugging_opts.mir_opt_level);
+                            let stmt_equality = self.statement_equality(*adt_matched_on, &l, bb_l_idx, &r, bb_r_idx, self.tcx);
                             if matches!(stmt_equality, StatementEquality::NotEqual) {
                                 // short circuit
                                 None
@@ -672,7 +672,7 @@ impl<'a, 'tcx> SimplifyBranchSameOptimizationFinder<'a, 'tcx> {
         x_bb_idx: BasicBlock,
         y: &Statement<'tcx>,
         y_bb_idx: BasicBlock,
-        mir_opt_level: usize,
+        tcx: TyCtxt<'tcx>,
     ) -> StatementEquality {
         let helper = |rhs: &Rvalue<'tcx>,
                       place: &Place<'tcx>,
@@ -693,7 +693,7 @@ impl<'a, 'tcx> SimplifyBranchSameOptimizationFinder<'a, 'tcx> {
                 Rvalue::Use(operand) if operand.place() == Some(adt_matched_on) => {
                     // FIXME(76803): This logic is currently broken because it does not take into
                     // account the current discriminant value.
-                    if mir_opt_level > 2 {
+                    if tcx.sess.opts.debugging_opts.unsound_mir_opts {
                         StatementEquality::ConsideredEqual(side_to_choose)
                     } else {
                         StatementEquality::NotEqual

compiler/rustc_session/src/options.rs

@@ -1115,6 +1115,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         `hir,typed` (HIR with types for each node),
         `hir-tree` (dump the raw HIR),
         `mir` (the MIR), or `mir-cfg` (graphviz formatted MIR)"),
+    unsound_mir_opts: bool = (false, parse_bool, [TRACKED],
+        "enable unsound and buggy MIR optimizations (default: no)"),
     unstable_options: bool = (false, parse_bool, [UNTRACKED],
         "adds unstable command line options to rustc interface (default: no)"),
     use_ctors_section: Option<bool> = (None, parse_opt_bool, [TRACKED],

src/test/mir-opt/copy_propagation.rs

@@ -1,3 +1,4 @@
+// compile-flags: -Zunsound-mir-opts
 // EMIT_MIR copy_propagation.test.CopyPropagation.diff
 
 fn test(x: u32) -> u32 {

src/test/mir-opt/copy_propagation.test.CopyPropagation.diff

@@ -2,19 +2,19 @@
 + // MIR for `test` after CopyPropagation
 
   fn test(_1: u32) -> u32 {
-      debug x => _1;                       // in scope 0 at $DIR/copy_propagation.rs:3:9: 3:10
-      let mut _0: u32;                     // return place in scope 0 at $DIR/copy_propagation.rs:3:20: 3:23
-      let _2: u32;                         // in scope 0 at $DIR/copy_propagation.rs:4:9: 4:10
+      debug x => _1;                       // in scope 0 at $DIR/copy_propagation.rs:4:9: 4:10
+      let mut _0: u32;                     // return place in scope 0 at $DIR/copy_propagation.rs:4:20: 4:23
+      let _2: u32;                         // in scope 0 at $DIR/copy_propagation.rs:5:9: 5:10
       scope 1 {
-          debug y => _0;                   // in scope 1 at $DIR/copy_propagation.rs:4:9: 4:10
+          debug y => _0;                   // in scope 1 at $DIR/copy_propagation.rs:5:9: 5:10
       }
 
       bb0: {
-          nop;                             // scope 0 at $DIR/copy_propagation.rs:4:9: 4:10
-          _0 = _1;                         // scope 0 at $DIR/copy_propagation.rs:4:13: 4:14
-          nop;                             // scope 1 at $DIR/copy_propagation.rs:5:5: 5:6
-          nop;                             // scope 0 at $DIR/copy_propagation.rs:6:1: 6:2
-          return;                          // scope 0 at $DIR/copy_propagation.rs:6:2: 6:2
+          nop;                             // scope 0 at $DIR/copy_propagation.rs:5:9: 5:10
+          _0 = _1;                         // scope 0 at $DIR/copy_propagation.rs:5:13: 5:14
+          nop;                             // scope 1 at $DIR/copy_propagation.rs:6:5: 6:6
+          nop;                             // scope 0 at $DIR/copy_propagation.rs:7:1: 7:2
+          return;                          // scope 0 at $DIR/copy_propagation.rs:7:2: 7:2
       }
   }
 

src/test/mir-opt/early_otherwise_branch_68867.rs

@@ -1,5 +1,5 @@
 // ignore-tidy-linelength
-// compile-flags: -Z mir-opt-level=3
+// compile-flags: -Z mir-opt-level=3 -Zunsound-mir-opts
 
 // example from #68867
 type CSSFloat = f32;

src/test/mir-opt/inline/inline-closure-borrows-arg.rs

@@ -1,4 +1,4 @@
-// compile-flags: -Z span_free_formats
+// compile-flags: -Z span_free_formats -Zunsound-mir-opts
 
 // Tests that MIR inliner can handle closure arguments,
 // even when (#45894)

src/test/mir-opt/inline/inline_any_operand.bar.Inline.after.mir

@@ -4,13 +4,15 @@ fn bar() -> bool {
     let mut _0: bool;                    // return place in scope 0 at $DIR/inline-any-operand.rs:10:13: 10:17
     let _1: fn(i32, i32) -> bool {foo};  // in scope 0 at $DIR/inline-any-operand.rs:11:9: 11:10
     let mut _2: fn(i32, i32) -> bool {foo}; // in scope 0 at $DIR/inline-any-operand.rs:12:5: 12:6
-    let mut _3: i32;                     // in scope 0 at $DIR/inline-any-operand.rs:12:5: 12:13
-    let mut _4: i32;                     // in scope 0 at $DIR/inline-any-operand.rs:12:5: 12:13
+    let mut _5: i32;                     // in scope 0 at $DIR/inline-any-operand.rs:12:5: 12:13
+    let mut _6: i32;                     // in scope 0 at $DIR/inline-any-operand.rs:12:5: 12:13
     scope 1 {
         debug f => _1;                   // in scope 1 at $DIR/inline-any-operand.rs:11:9: 11:10
         scope 2 {
-            debug x => _3;               // in scope 2 at $DIR/inline-any-operand.rs:16:8: 16:9
-            debug y => _4;               // in scope 2 at $DIR/inline-any-operand.rs:16:16: 16:17
+            debug x => _5;               // in scope 2 at $DIR/inline-any-operand.rs:16:8: 16:9
+            debug y => _6;               // in scope 2 at $DIR/inline-any-operand.rs:16:16: 16:17
+            let mut _3: i32;             // in scope 2 at $DIR/inline-any-operand.rs:12:5: 12:13
+            let mut _4: i32;             // in scope 2 at $DIR/inline-any-operand.rs:12:5: 12:13
         }
     }
 
@@ -22,13 +24,19 @@ fn bar() -> bool {
                                          // + literal: Const { ty: fn(i32, i32) -> bool {foo}, val: Value(Scalar(<ZST>)) }
         StorageLive(_2);                 // scope 1 at $DIR/inline-any-operand.rs:12:5: 12:6
         _2 = _1;                         // scope 1 at $DIR/inline-any-operand.rs:12:5: 12:6
-        StorageLive(_3);                 // scope 1 at $DIR/inline-any-operand.rs:12:5: 12:13
-        _3 = const 1_i32;                // scope 1 at $DIR/inline-any-operand.rs:12:5: 12:13
-        StorageLive(_4);                 // scope 1 at $DIR/inline-any-operand.rs:12:5: 12:13
-        _4 = const -1_i32;               // scope 1 at $DIR/inline-any-operand.rs:12:5: 12:13
+        StorageLive(_5);                 // scope 1 at $DIR/inline-any-operand.rs:12:5: 12:13
+        _5 = const 1_i32;                // scope 1 at $DIR/inline-any-operand.rs:12:5: 12:13
+        StorageLive(_6);                 // scope 1 at $DIR/inline-any-operand.rs:12:5: 12:13
+        _6 = const -1_i32;               // scope 1 at $DIR/inline-any-operand.rs:12:5: 12:13
+        StorageLive(_3);                 // scope 2 at $DIR/inline-any-operand.rs:17:5: 17:6
+        _3 = _5;                         // scope 2 at $DIR/inline-any-operand.rs:17:5: 17:6
+        StorageLive(_4);                 // scope 2 at $DIR/inline-any-operand.rs:17:10: 17:11
+        _4 = _6;                         // scope 2 at $DIR/inline-any-operand.rs:17:10: 17:11
         _0 = Eq(move _3, move _4);       // scope 2 at $DIR/inline-any-operand.rs:17:5: 17:11
-        StorageDead(_4);                 // scope 1 at $DIR/inline-any-operand.rs:12:5: 12:13
-        StorageDead(_3);                 // scope 1 at $DIR/inline-any-operand.rs:12:5: 12:13
+        StorageDead(_4);                 // scope 2 at $DIR/inline-any-operand.rs:17:10: 17:11
+        StorageDead(_3);                 // scope 2 at $DIR/inline-any-operand.rs:17:10: 17:11
+        StorageDead(_6);                 // scope 1 at $DIR/inline-any-operand.rs:12:5: 12:13
+        StorageDead(_5);                 // scope 1 at $DIR/inline-any-operand.rs:12:5: 12:13
         StorageDead(_2);                 // scope 1 at $DIR/inline-any-operand.rs:12:12: 12:13
         StorageDead(_1);                 // scope 0 at $DIR/inline-any-operand.rs:13:1: 13:2
         return;                          // scope 0 at $DIR/inline-any-operand.rs:13:2: 13:2

src/test/mir-opt/inline/inline_trait_method_2.test2.Inline.after.mir

@@ -7,6 +7,7 @@ fn test2(_1: &dyn X) -> bool {
     let mut _3: &dyn X;                  // in scope 0 at $DIR/inline-trait-method_2.rs:5:10: 5:11
     scope 1 {
         debug x => _2;                   // in scope 1 at $DIR/inline-trait-method_2.rs:9:9: 9:10
+        let mut _4: &dyn X;              // in scope 1 at $DIR/inline-trait-method_2.rs:5:5: 5:12
     }
 
     bb0: {
@@ -15,13 +16,16 @@ fn test2(_1: &dyn X) -> bool {
         _3 = &(*_1);                     // scope 0 at $DIR/inline-trait-method_2.rs:5:10: 5:11
         _2 = move _3 as &dyn X (Pointer(Unsize)); // scope 0 at $DIR/inline-trait-method_2.rs:5:10: 5:11
         StorageDead(_3);                 // scope 0 at $DIR/inline-trait-method_2.rs:5:10: 5:11
-        _0 = <dyn X as X>::y(move _2) -> bb1; // scope 1 at $DIR/inline-trait-method_2.rs:10:5: 10:10
+        StorageLive(_4);                 // scope 1 at $DIR/inline-trait-method_2.rs:10:5: 10:6
+        _4 = _2;                         // scope 1 at $DIR/inline-trait-method_2.rs:10:5: 10:6
+        _0 = <dyn X as X>::y(move _4) -> bb1; // scope 1 at $DIR/inline-trait-method_2.rs:10:5: 10:10
                                          // mir::Constant
                                          // + span: $DIR/inline-trait-method_2.rs:10:7: 10:8
                                          // + literal: Const { ty: for<'r> fn(&'r dyn X) -> bool {<dyn X as X>::y}, val: Value(Scalar(<ZST>)) }
     }
 
     bb1: {
+        StorageDead(_4);                 // scope 1 at $DIR/inline-trait-method_2.rs:10:9: 10:10
         StorageDead(_2);                 // scope 0 at $DIR/inline-trait-method_2.rs:5:11: 5:12
         return;                          // scope 0 at $DIR/inline-trait-method_2.rs:6:2: 6:2
     }