Auto merge of #83417 - erikdesjardins:enableremovezsts, r=oli-obk

Run RemoveZsts pass at mir-opt-level=1

per https://github.com/rust-lang/rust/pull/83177#issuecomment-803942217

This pass removes assignments to ZST places.

Perf (from https://github.com/rust-lang/rust/pull/83177#issuecomment-803442557): https://perf.rust-lang.org/compare.html?start=41b315a470d583f6446599984ff9ad3bd61012b2&end=bd5d1b96f0c64c9938feea831789e1b5bb2cd4a2

r? `@oli-obk`

compiler/rustc_mir/src/transform/remove_zsts.rs

@@ -9,9 +9,6 @@
 
 impl<'tcx> MirPass<'tcx> for RemoveZsts {
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        if tcx.sess.mir_opt_level() < 3 {
-            return;
-        }
         let param_env = tcx.param_env(body.source.def_id());
         let (basic_blocks, local_decls) = body.basic_blocks_and_local_decls_mut();
         for block in basic_blocks.iter_mut() {

src/test/incremental/hashes/trait_impls.rs

@@ -62,7 +62,7 @@ fn method_name() { }
 #[rustc_clean(cfg="cfail2")]
 #[rustc_clean(cfg="cfail3")]
 impl ChangeMethodBodyTrait for Foo {
-    #[rustc_clean(except="hir_owner_nodes,typeck,optimized_mir", cfg="cfail2")]
+    #[rustc_clean(except="hir_owner_nodes,typeck", cfg="cfail2")]
     #[rustc_clean(cfg="cfail3")]
     fn method_name() {
         ()

src/test/mir-opt/const_prop/control_flow_simplification.hello.ConstProp.diff

@@ -29,7 +29,7 @@
       }
   
       bb2: {
-          _0 = const ();                   // scope 0 at $DIR/control-flow-simplification.rs:14:6: 14:6
+          nop;                             // scope 0 at $DIR/control-flow-simplification.rs:14:6: 14:6
           StorageDead(_1);                 // scope 0 at $DIR/control-flow-simplification.rs:14:5: 14:6
           return;                          // scope 0 at $DIR/control-flow-simplification.rs:15:2: 15:2
       }

src/test/mir-opt/const_prop/control_flow_simplification.hello.PreCodegen.before.mir

@@ -4,7 +4,6 @@ fn hello() -> () {
     let mut _0: ();                      // return place in scope 0 at $DIR/control-flow-simplification.rs:11:14: 11:14
 
     bb0: {
-        _0 = const ();                   // scope 0 at $DIR/control-flow-simplification.rs:14:6: 14:6
         return;                          // scope 0 at $DIR/control-flow-simplification.rs:15:2: 15:2
     }
 }

src/test/mir-opt/remove_unneeded_drops.cannot_opt_generic.RemoveUnneededDrops.diff

@@ -14,7 +14,6 @@
           StorageLive(_2);                 // scope 0 at $DIR/remove_unneeded_drops.rs:21:5: 21:12
           StorageLive(_3);                 // scope 0 at $DIR/remove_unneeded_drops.rs:21:10: 21:11
           _3 = move _1;                    // scope 0 at $DIR/remove_unneeded_drops.rs:21:10: 21:11
-          nop;                             // scope 1 at $DIR/remove_unneeded_drops.rs:21:5: 21:12
           drop(_3) -> [return: bb2, unwind: bb1]; // scope 1 at $DIR/remove_unneeded_drops.rs:21:5: 21:12
       }
   

src/test/mir-opt/remove_unneeded_drops.dont_opt.RemoveUnneededDrops.diff

@@ -14,7 +14,6 @@
           StorageLive(_2);                 // scope 0 at $DIR/remove_unneeded_drops.rs:9:5: 9:12
           StorageLive(_3);                 // scope 0 at $DIR/remove_unneeded_drops.rs:9:10: 9:11
           _3 = move _1;                    // scope 0 at $DIR/remove_unneeded_drops.rs:9:10: 9:11
-          nop;                             // scope 1 at $DIR/remove_unneeded_drops.rs:9:5: 9:12
           drop(_3) -> [return: bb2, unwind: bb1]; // scope 1 at $DIR/remove_unneeded_drops.rs:9:5: 9:12
       }
   

src/test/mir-opt/remove_unneeded_drops.opt.RemoveUnneededDrops.diff

@@ -14,7 +14,6 @@
           StorageLive(_2);                 // scope 0 at $DIR/remove_unneeded_drops.rs:4:5: 4:12
           StorageLive(_3);                 // scope 0 at $DIR/remove_unneeded_drops.rs:4:10: 4:11
           _3 = _1;                         // scope 0 at $DIR/remove_unneeded_drops.rs:4:10: 4:11
--         nop;                             // scope 1 at $DIR/remove_unneeded_drops.rs:4:5: 4:12
 -         drop(_3) -> bb1;                 // scope 1 at $DIR/remove_unneeded_drops.rs:4:5: 4:12
 -     }
 - 

src/test/mir-opt/remove_unneeded_drops.opt_generic_copy.RemoveUnneededDrops.diff

@@ -14,7 +14,6 @@
           StorageLive(_2);                 // scope 0 at $DIR/remove_unneeded_drops.rs:14:5: 14:12
           StorageLive(_3);                 // scope 0 at $DIR/remove_unneeded_drops.rs:14:10: 14:11
           _3 = _1;                         // scope 0 at $DIR/remove_unneeded_drops.rs:14:10: 14:11
--         nop;                             // scope 1 at $DIR/remove_unneeded_drops.rs:14:5: 14:12
 -         drop(_3) -> bb1;                 // scope 1 at $DIR/remove_unneeded_drops.rs:14:5: 14:12
 -     }
 - 

src/test/mir-opt/simplify_locals_fixedpoint.foo.SimplifyLocals.diff

@@ -9,8 +9,8 @@
       let mut _4: isize;                   // in scope 0 at $DIR/simplify-locals-fixedpoint.rs:4:22: 4:26
       let mut _5: isize;                   // in scope 0 at $DIR/simplify-locals-fixedpoint.rs:4:13: 4:20
       let _6: u8;                          // in scope 0 at $DIR/simplify-locals-fixedpoint.rs:4:18: 4:19
-      let mut _7: bool;                    // in scope 0 at $DIR/simplify-locals-fixedpoint.rs:5:12: 5:20
-      let mut _8: u8;                      // in scope 0 at $DIR/simplify-locals-fixedpoint.rs:5:12: 5:13
+-     let mut _7: bool;                    // in scope 0 at $DIR/simplify-locals-fixedpoint.rs:5:12: 5:20
+-     let mut _8: u8;                      // in scope 0 at $DIR/simplify-locals-fixedpoint.rs:5:12: 5:13
       scope 1 {
           debug a => _6;                   // in scope 1 at $DIR/simplify-locals-fixedpoint.rs:4:18: 4:19
       }
@@ -26,51 +26,32 @@
           StorageDead(_3);                 // scope 0 at $DIR/simplify-locals-fixedpoint.rs:4:68: 4:69
           StorageDead(_2);                 // scope 0 at $DIR/simplify-locals-fixedpoint.rs:4:68: 4:69
           _5 = discriminant((_1.0: std::option::Option<u8>)); // scope 0 at $DIR/simplify-locals-fixedpoint.rs:4:13: 4:20
-          switchInt(move _5) -> [1_isize: bb2, otherwise: bb1]; // scope 0 at $DIR/simplify-locals-fixedpoint.rs:4:13: 4:20
+          switchInt(move _5) -> [1_isize: bb1, otherwise: bb3]; // scope 0 at $DIR/simplify-locals-fixedpoint.rs:4:13: 4:20
       }
   
       bb1: {
-          _0 = const ();                   // scope 0 at $DIR/simplify-locals-fixedpoint.rs:8:6: 8:6
-          goto -> bb7;                     // scope 0 at $DIR/simplify-locals-fixedpoint.rs:4:5: 8:6
-      }
-  
-      bb2: {
           _4 = discriminant((_1.1: std::option::Option<T>)); // scope 0 at $DIR/simplify-locals-fixedpoint.rs:4:22: 4:26
-          switchInt(move _4) -> [0_isize: bb3, otherwise: bb1]; // scope 0 at $DIR/simplify-locals-fixedpoint.rs:4:22: 4:26
+          switchInt(move _4) -> [0_isize: bb2, otherwise: bb3]; // scope 0 at $DIR/simplify-locals-fixedpoint.rs:4:22: 4:26
       }
   
-      bb3: {
+      bb2: {
           StorageLive(_6);                 // scope 0 at $DIR/simplify-locals-fixedpoint.rs:4:18: 4:19
           _6 = (((_1.0: std::option::Option<u8>) as Some).0: u8); // scope 0 at $DIR/simplify-locals-fixedpoint.rs:4:18: 4:19
-          StorageLive(_7);                 // scope 1 at $DIR/simplify-locals-fixedpoint.rs:5:12: 5:20
-          StorageLive(_8);                 // scope 1 at $DIR/simplify-locals-fixedpoint.rs:5:12: 5:13
-          _8 = _6;                         // scope 1 at $DIR/simplify-locals-fixedpoint.rs:5:12: 5:13
-          _7 = Gt(move _8, const 42_u8);   // scope 1 at $DIR/simplify-locals-fixedpoint.rs:5:12: 5:20
-          StorageDead(_8);                 // scope 1 at $DIR/simplify-locals-fixedpoint.rs:5:19: 5:20
-          switchInt(move _7) -> [false: bb5, otherwise: bb4]; // scope 1 at $DIR/simplify-locals-fixedpoint.rs:5:9: 7:10
-      }
-  
-      bb4: {
-          _0 = const ();                   // scope 1 at $DIR/simplify-locals-fixedpoint.rs:5:21: 7:10
-          goto -> bb6;                     // scope 1 at $DIR/simplify-locals-fixedpoint.rs:5:9: 7:10
-      }
-  
-      bb5: {
-          _0 = const ();                   // scope 1 at $DIR/simplify-locals-fixedpoint.rs:7:10: 7:10
-          goto -> bb6;                     // scope 1 at $DIR/simplify-locals-fixedpoint.rs:5:9: 7:10
-      }
-  
-      bb6: {
-          StorageDead(_7);                 // scope 1 at $DIR/simplify-locals-fixedpoint.rs:7:9: 7:10
+-         StorageLive(_7);                 // scope 1 at $DIR/simplify-locals-fixedpoint.rs:5:12: 5:20
+-         StorageLive(_8);                 // scope 1 at $DIR/simplify-locals-fixedpoint.rs:5:12: 5:13
+-         _8 = _6;                         // scope 1 at $DIR/simplify-locals-fixedpoint.rs:5:12: 5:13
+-         _7 = Gt(move _8, const 42_u8);   // scope 1 at $DIR/simplify-locals-fixedpoint.rs:5:12: 5:20
+-         StorageDead(_8);                 // scope 1 at $DIR/simplify-locals-fixedpoint.rs:5:19: 5:20
+-         StorageDead(_7);                 // scope 1 at $DIR/simplify-locals-fixedpoint.rs:7:9: 7:10
           StorageDead(_6);                 // scope 0 at $DIR/simplify-locals-fixedpoint.rs:8:5: 8:6
-          goto -> bb7;                     // scope 0 at $DIR/simplify-locals-fixedpoint.rs:4:5: 8:6
+          goto -> bb3;                     // scope 0 at $DIR/simplify-locals-fixedpoint.rs:4:5: 8:6
       }
   
-      bb7: {
-          drop(_1) -> bb8;                 // scope 0 at $DIR/simplify-locals-fixedpoint.rs:9:1: 9:2
+      bb3: {
+          drop(_1) -> bb4;                 // scope 0 at $DIR/simplify-locals-fixedpoint.rs:9:1: 9:2
       }
   
-      bb8: {
+      bb4: {
           StorageDead(_1);                 // scope 0 at $DIR/simplify-locals-fixedpoint.rs:9:1: 9:2
           return;                          // scope 0 at $DIR/simplify-locals-fixedpoint.rs:9:2: 9:2
       }

src/test/run-make/const_fn_mir/dump.mir

@@ -12,7 +12,6 @@ fn main() -> () {
     }
 
     bb1: {
-        _0 = const ();                   // scope 0 at main.rs:8:11: 10:2
         return;                          // scope 0 at main.rs:10:2: 10:2
     }
 }

src/test/ui/consts/const-eval/panic-assoc-never-type.rs

@@ -14,5 +14,4 @@ impl PrintName {
 
 fn main() {
     let _ = PrintName::VOID;
-    //~^ ERROR erroneous constant used
 }

src/test/ui/consts/const-eval/panic-assoc-never-type.stderr

@@ -6,12 +6,6 @@ LL |     const VOID: ! = panic!();
    |
    = note: this error originates in the macro `$crate::panic::panic_2015` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0080]: erroneous constant used
-  --> $DIR/panic-assoc-never-type.rs:16:13
-   |
-LL |     let _ = PrintName::VOID;
-   |             ^^^^^^^^^^^^^^^ referenced constant has errors
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
 For more information about this error, try `rustc --explain E0080`.

src/test/ui/recursion/issue-26548-recursion-via-normalize.stderr

-error[E0391]: cycle detected when computing layout of `S`
+error[E0391]: cycle detected when computing layout of `std::option::Option<S>`
    |
-   = note: ...which requires computing layout of `std::option::Option<S>`...
-   = note: ...which again requires computing layout of `S`, completing the cycle
+   = note: ...which requires computing layout of `S`...
+   = note: ...which again requires computing layout of `std::option::Option<S>`, completing the cycle
 note: cycle used when optimizing MIR for `main`
   --> $DIR/issue-26548-recursion-via-normalize.rs:15:1
    |