Enable DestinationPropagation by default.

Author: cjgillot

Diff for: compiler/rustc_mir_transform/src/dest_prop.rs

@@ -159,7 +159,7 @@ impl<'tcx> MirPass<'tcx> for DestinationPropagation {
         //  2. Despite being an overall perf improvement, this still causes a 30% regression in
         //     keccak. We can temporarily fix this by bounding function size, but in the long term
         //     we should fix this by being smarter about invalidating analysis results.
-        sess.mir_opt_level() >= 3
+        sess.mir_opt_level() >= 2
     }
 
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {

Diff for: compiler/rustc_mir_transform/src/lib.rs

@@ -90,7 +90,6 @@ mod match_branches;
 mod mentioned_items;
 mod multiple_return_terminators;
 mod normalize_array_len;
-mod nrvo;
 mod prettify;
 mod promote_consts;
 mod ref_prop;
@@ -598,13 +597,12 @@ fn run_optimization_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
             &jump_threading::JumpThreading,
             &early_otherwise_branch::EarlyOtherwiseBranch,
             &simplify_comparison_integral::SimplifyComparisonIntegral,
-            &dest_prop::DestinationPropagation,
             &o1(simplify_branches::SimplifyConstCondition::Final),
             &o1(remove_noop_landing_pads::RemoveNoopLandingPads),
             &o1(simplify::SimplifyCfg::Final),
             &copy_prop::CopyProp,
             &dead_store_elimination::DeadStoreElimination::Final,
-            &nrvo::RenameReturnPlace,
+            &dest_prop::DestinationPropagation,
             &simplify::SimplifyLocals::Final,
             &multiple_return_terminators::MultipleReturnTerminators,
             &deduplicate_blocks::DeduplicateBlocks,

Diff for: compiler/rustc_mir_transform/src/nrvo.rs

@@ -1,5 +1,5 @@
-- // MIR for `nrvo` before RenameReturnPlace
-+ // MIR for `nrvo` after RenameReturnPlace
+- // MIR for `nrvo` before DestinationPropagation
++ // MIR for `nrvo` after DestinationPropagation
 
   fn nrvo(_1: for<'a> fn(&'a mut [u8; 1024])) -> [u8; 1024] {
       debug init => _1;
@@ -10,32 +10,33 @@
       let mut _5: &mut [u8; 1024];
       let mut _6: &mut [u8; 1024];
       scope 1 {
--         debug buf => _2;
-+         debug buf => _0;
+          debug buf => _2;
       }
 
       bb0: {
--         StorageLive(_2);
--         _2 = [const 0_u8; 1024];
-+         _0 = [const 0_u8; 1024];
+          StorageLive(_2);
+          _2 = [const 0_u8; 1024];
           StorageLive(_3);
-          StorageLive(_4);
-          _4 = _1;
+-         StorageLive(_4);
+-         _4 = _1;
++         nop;
++         nop;
           StorageLive(_5);
           StorageLive(_6);
--         _6 = &mut _2;
-+         _6 = &mut _0;
+          _6 = &mut _2;
           _5 = &mut (*_6);
-          _3 = move _4(move _5) -> [return: bb1, unwind unreachable];
+-         _3 = move _4(move _5) -> [return: bb1, unwind unreachable];
++         _3 = move _1(move _5) -> [return: bb1, unwind unreachable];
       }
 
       bb1: {
           StorageDead(_5);
-          StorageDead(_4);
+-         StorageDead(_4);
++         nop;
           StorageDead(_6);
           StorageDead(_3);
--         _0 = _2;
--         StorageDead(_2);
+          _0 = _2;
+          StorageDead(_2);
           return;
       }
   }

Diff for: tests/mir-opt/nrvo_simple.nrvo.RenameReturnPlace.panic-abort.diff renamed to tests/mir-opt/dest-prop/nrvo_borrowed.nrvo.DestinationPropagation.panic-abort.diff

@@ -1,5 +1,5 @@
-- // MIR for `nrvo` before RenameReturnPlace
-+ // MIR for `nrvo` after RenameReturnPlace
+- // MIR for `nrvo` before DestinationPropagation
++ // MIR for `nrvo` after DestinationPropagation
 
   fn nrvo(_1: for<'a> fn(&'a mut [u8; 1024])) -> [u8; 1024] {
       debug init => _1;
@@ -10,32 +10,33 @@
       let mut _5: &mut [u8; 1024];
       let mut _6: &mut [u8; 1024];
       scope 1 {
--         debug buf => _2;
-+         debug buf => _0;
+          debug buf => _2;
       }
 
       bb0: {
--         StorageLive(_2);
--         _2 = [const 0_u8; 1024];
-+         _0 = [const 0_u8; 1024];
+          StorageLive(_2);
+          _2 = [const 0_u8; 1024];
           StorageLive(_3);
-          StorageLive(_4);
-          _4 = _1;
+-         StorageLive(_4);
+-         _4 = _1;
++         nop;
++         nop;
           StorageLive(_5);
           StorageLive(_6);
--         _6 = &mut _2;
-+         _6 = &mut _0;
+          _6 = &mut _2;
           _5 = &mut (*_6);
-          _3 = move _4(move _5) -> [return: bb1, unwind continue];
+-         _3 = move _4(move _5) -> [return: bb1, unwind continue];
++         _3 = move _1(move _5) -> [return: bb1, unwind continue];
       }
 
       bb1: {
           StorageDead(_5);
-          StorageDead(_4);
+-         StorageDead(_4);
++         nop;
           StorageDead(_6);
           StorageDead(_3);
--         _0 = _2;
--         StorageDead(_2);
+          _0 = _2;
+          StorageDead(_2);
           return;
       }
   }

Diff for: tests/mir-opt/nrvo_simple.nrvo.RenameReturnPlace.panic-unwind.diff renamed to tests/mir-opt/dest-prop/nrvo_borrowed.nrvo.DestinationPropagation.panic-unwind.diff

@@ -1,8 +1,8 @@
 // skip-filecheck
 // EMIT_MIR_FOR_EACH_PANIC_STRATEGY
-//@ unit-test: RenameReturnPlace
+//@ unit-test: DestinationPropagation
 
-// EMIT_MIR nrvo_simple.nrvo.RenameReturnPlace.diff
+// EMIT_MIR nrvo_borrowed.nrvo.DestinationPropagation.diff
 fn nrvo(init: fn(&mut [u8; 1024])) -> [u8; 1024] {
     let mut buf = [0; 1024];
     init(&mut buf);

Diff for: tests/mir-opt/nrvo_simple.rs renamed to tests/mir-opt/dest-prop/nrvo_borrowed.rs

@@ -18,7 +18,7 @@
       bb0: {
           StorageLive(_1);
           StorageLive(_2);
-          _2 = const 1_u32;
+          nop;
           _1 = Un { us: const 1_u32 };
           StorageDead(_2);
           StorageLive(_3);