dse: Remove a pair of unused StorageLive and StorageDead statements

dianqk · dianqk · commit faddcfc8af9f · 2024-08-26T22:05:25.000+08:00
diff --git a/compiler/rustc_mir_transform/src/dead_store_elimination.rs b/compiler/rustc_mir_transform/src/dead_store_elimination.rs
@@ -13,7 +13,7 @@
 //!
 
 use rustc_middle::bug;
-use rustc_middle::mir::visit::Visitor;
+use rustc_middle::mir::visit::*;
 use rustc_middle::mir::*;
 use rustc_middle::ty::TyCtxt;
 use rustc_mir_dataflow::debuginfo::debuginfo_locals;
@@ -95,7 +95,7 @@ pub fn eliminate<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
                     if !place.is_indirect() && !always_live.contains(place.local) {
                         live.seek_before_primary_effect(loc);
                         if !live.get().contains(place.local) {
-                            patch.push(loc);
+                            patch.push((place.local, loc));
                         }
                     }
                 }
@@ -120,8 +120,29 @@ pub fn eliminate<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     }
 
     let bbs = body.basic_blocks.as_mut_preserves_cfg();
-    for Location { block, statement_index } in patch {
+    for (local, Location { block, statement_index }) in patch {
         bbs[block].statements[statement_index].make_nop();
+        // Remove a pair of unused `StorageLive` and `StorageDead` statements if we found it.
+        if bbs[block].statements.iter().all(|stmt| match stmt.kind {
+            StatementKind::Assign(box (place, _))
+            | StatementKind::SetDiscriminant { place: box place, .. }
+            | StatementKind::Deinit(box place) => place.local != local,
+            _ => true,
+        }) && let Some(storage_live_index) = bbs[block]
+            .statements
+            .iter()
+            .take(statement_index)
+            .position(|stmt| stmt.kind == StatementKind::StorageLive(local))
+            && let Some(storage_dead_index) = bbs[block]
+                .statements
+                .iter()
+                .skip(statement_index)
+                .position(|stmt| stmt.kind == StatementKind::StorageDead(local))
+                .map(|p| p + statement_index)
+        {
+            bbs[block].statements[storage_live_index].make_nop();
+            bbs[block].statements[storage_dead_index].make_nop();
+        }
     }
     for (block, argument_index) in call_operands_to_move {
         let TerminatorKind::Call { ref mut args, .. } = bbs[block].terminator_mut().kind else {
diff --git a/tests/mir-opt/issue_76432.test.SimplifyComparisonIntegral.panic-abort.diff b/tests/mir-opt/issue_76432.test.SimplifyComparisonIntegral.panic-abort.diff
@@ -37,12 +37,6 @@
       }
   
       bb2: {
-          StorageLive(_7);
-          StorageLive(_8);
-          StorageLive(_9);
-          StorageDead(_9);
-          StorageDead(_8);
-          StorageDead(_7);
           StorageDead(_4);
           return;
       }
diff --git a/tests/mir-opt/issue_76432.test.SimplifyComparisonIntegral.panic-unwind.diff b/tests/mir-opt/issue_76432.test.SimplifyComparisonIntegral.panic-unwind.diff
@@ -37,12 +37,6 @@
       }
   
       bb2: {
-          StorageLive(_7);
-          StorageLive(_8);
-          StorageLive(_9);
-          StorageDead(_9);
-          StorageDead(_8);
-          StorageDead(_7);
           StorageDead(_4);
           return;
       }
diff --git a/tests/mir-opt/pre-codegen/issue_117368_print_invalid_constant.main.GVN.32bit.panic-abort.diff b/tests/mir-opt/pre-codegen/issue_117368_print_invalid_constant.main.GVN.32bit.panic-abort.diff
@@ -102,10 +102,10 @@
           StorageDead(_16);
           StorageDead(_12);
           StorageDead(_6);
-          StorageLive(_17);
           nop;
           nop;
-          StorageDead(_17);
+          nop;
+          nop;
           StorageDead(_5);
           nop;
           StorageDead(_4);
diff --git a/tests/mir-opt/pre-codegen/issue_117368_print_invalid_constant.main.GVN.32bit.panic-unwind.diff b/tests/mir-opt/pre-codegen/issue_117368_print_invalid_constant.main.GVN.32bit.panic-unwind.diff
@@ -45,10 +45,10 @@
   
       bb1: {
           StorageDead(_6);
-          StorageLive(_12);
           nop;
           nop;
-          StorageDead(_12);
+          nop;
+          nop;
           StorageDead(_5);
           nop;
           StorageDead(_4);
diff --git a/tests/mir-opt/pre-codegen/issue_117368_print_invalid_constant.main.GVN.64bit.panic-abort.diff b/tests/mir-opt/pre-codegen/issue_117368_print_invalid_constant.main.GVN.64bit.panic-abort.diff
@@ -102,10 +102,10 @@
           StorageDead(_16);
           StorageDead(_12);
           StorageDead(_6);
-          StorageLive(_17);
           nop;
           nop;
-          StorageDead(_17);
+          nop;
+          nop;
           StorageDead(_5);
           nop;
           StorageDead(_4);
diff --git a/tests/mir-opt/pre-codegen/issue_117368_print_invalid_constant.main.GVN.64bit.panic-unwind.diff b/tests/mir-opt/pre-codegen/issue_117368_print_invalid_constant.main.GVN.64bit.panic-unwind.diff
@@ -45,10 +45,10 @@
   
       bb1: {
           StorageDead(_6);
-          StorageLive(_12);
           nop;
           nop;
-          StorageDead(_12);
+          nop;
+          nop;
           StorageDead(_5);
           nop;
           StorageDead(_4);
diff --git a/tests/mir-opt/pre-codegen/loops.vec_move.PreCodegen.after.mir b/tests/mir-opt/pre-codegen/loops.vec_move.PreCodegen.after.mir
@@ -208,31 +208,32 @@ fn vec_move(_1: Vec<impl Sized>) -> () {
         _5 = move (((_1.0: alloc::raw_vec::RawVec<impl Sized>).0: alloc::raw_vec::RawVecInner).2: std::alloc::Global);
         _6 = move ((_1.0: alloc::raw_vec::RawVec<impl Sized>).1: std::marker::PhantomData<impl Sized>);
         _7 = move (_1.1: usize);
+        StorageLive(_29);
+        StorageLive(_30);
+        StorageLive(_31);
         StorageLive(_10);
+        StorageLive(_32);
+        StorageLive(_33);
         StorageLive(_11);
+        StorageLive(_34);
+        StorageLive(_35);
+        StorageLive(_36);
+        StorageLive(_37);
+        StorageLive(_39);
         StorageLive(_9);
         StorageLive(_8);
         StorageLive(_16);
+        StorageLive(_46);
         StorageLive(_28);
-        StorageLive(_29);
-        StorageLive(_30);
-        StorageLive(_31);
-        StorageDead(_31);
         StorageLive(_40);
         StorageLive(_41);
         StorageDead(_41);
         StorageDead(_40);
-        StorageDead(_30);
-        StorageDead(_29);
-        StorageLive(_32);
-        StorageLive(_33);
-        StorageDead(_33);
         StorageLive(_42);
         _8 = copy (_2.0: *const u8);
         _9 = copy _8 as *const impl Sized (PtrToPtr);
         _10 = NonNull::<impl Sized> { pointer: copy _9 };
         StorageDead(_42);
-        StorageDead(_32);
         _11 = copy _8 as *mut impl Sized (PtrToPtr);
         StorageLive(_14);
         switchInt(const <impl Sized as std::mem::SizedTypeProperties>::IS_ZST) -> [0: bb1, otherwise: bb2];
@@ -241,10 +242,6 @@ fn vec_move(_1: Vec<impl Sized>) -> () {
     bb1: {
         StorageLive(_13);
         StorageLive(_12);
-        StorageLive(_36);
-        StorageLive(_37);
-        StorageDead(_37);
-        StorageDead(_36);
         _12 = Offset(copy _11, copy _7);
         _13 = move _12 as *const impl Sized (PtrToPtr);
         StorageDead(_12);
@@ -254,10 +251,7 @@ fn vec_move(_1: Vec<impl Sized>) -> () {
     }
 
     bb2: {
-        StorageLive(_34);
-        StorageLive(_35);
-        StorageDead(_35);
-        StorageDead(_34);
+        StorageLive(_45);
         StorageLive(_43);
         StorageLive(_44);
         StorageLive(_15);
@@ -268,20 +262,15 @@ fn vec_move(_1: Vec<impl Sized>) -> () {
     bb3: {
         StorageDead(_15);
         StorageDead(_44);
-        StorageLive(_45);
-        StorageLive(_46);
-        StorageDead(_46);
-        StorageDead(_45);
         StorageDead(_43);
+        StorageDead(_45);
         _14 = copy _16 as *const impl Sized (PtrToPtr);
         goto -> bb4;
     }
 
     bb4: {
         StorageLive(_18);
         StorageLive(_38);
-        StorageLive(_39);
-        StorageDead(_39);
         StorageLive(_47);
         StorageLive(_17);
         _17 = SizeOf(impl Sized);
@@ -312,11 +301,22 @@ fn vec_move(_1: Vec<impl Sized>) -> () {
         StorageDead(_18);
         StorageDead(_14);
         StorageDead(_28);
+        StorageDead(_46);
         StorageDead(_16);
         StorageDead(_8);
         StorageDead(_9);
+        StorageDead(_39);
+        StorageDead(_37);
+        StorageDead(_36);
+        StorageDead(_35);
+        StorageDead(_34);
         StorageDead(_11);
+        StorageDead(_33);
+        StorageDead(_32);
         StorageDead(_10);
+        StorageDead(_31);
+        StorageDead(_30);
+        StorageDead(_29);
         StorageDead(_3);
         StorageDead(_4);
         StorageDead(_5);
diff --git a/tests/mir-opt/separate_const_switch.too_complex.JumpThreading.diff b/tests/mir-opt/separate_const_switch.too_complex.JumpThreading.diff
@@ -54,9 +54,7 @@
       }
   
       bb5: {
-          StorageLive(_8);
           _0 = const Option::<i32>::None;
-          StorageDead(_8);
           goto -> bb7;
       }
   

Original file line number	Diff line number	Diff line change
`@@ -37,12 +37,6 @@`
`37`	`37`	`}`
`38`	`38`
`39`	`39`	`bb2: {`
`40`		`- StorageLive(_7);`
`41`		`- StorageLive(_8);`
`42`		`- StorageLive(_9);`
`43`		`- StorageDead(_9);`
`44`		`- StorageDead(_8);`
`45`		`- StorageDead(_7);`
`46`	`40`	`StorageDead(_4);`
`47`	`41`	`return;`
`48`	`42`	`}`
Original file line number	Diff line number	Diff line change
`@@ -54,9 +54,7 @@`
`54`	`54`	`}`
`55`	`55`
`56`	`56`	`bb5: {`
`57`		`- StorageLive(_8);`
`58`	`57`	`_0 = const Option::<i32>::None;`
`59`		`- StorageDead(_8);`
`60`	`58`	`goto -> bb7;`
`61`	`59`	`}`
`62`	`60`