[CanOSSALife] Lexical lifetimes go to unreachables

When canonicalizing the lifetime of a lexical value, deinit barriers are
respected. This is done by walking backwards from lifetime ends and
adding encountered deinit barriers to liveness.

Only destroy lifetime ends were walked back from under the assumption
that lifetimes would be complete. Without complete OSSA lifetimes,
however, it's necessary to also necessary to consider lifetimes that end
with unreachables. Unfortunately, we can't simply walk back from those
unreachables because there may be instructions which are secretly users
of the value being canonicalized (e.g. destroys of `partial_apply`s to
which a `begin_borrow` of the value was passed). Such uses don't appear
in the use list because lifetime canonicalization expects complete
lifetimes and only visits lifetime ends of `begin_borrow`s.

Here, instead, the instructions before the relevant unreachables are
added to liveness. In order to determine which unreachables are
relevant, it's necessary to have a liveness that includes the original
destroys. So a copy of liveness is created and those destroys are added
to it.

rdar://115468707

Author: nate-chandler

include/swift/SILOptimizer/Utils/CanonicalizeOSSALifetime.h

@@ -319,7 +319,7 @@ class CanonicalizeOSSALifetime final {
 
     currentDef = def;
 
-    if (maximizeLifetime) {
+    if (maximizeLifetime || respectsDeinitBarriers()) {
       liveness->initializeDiscoveredBlocks(&discoveredBlocks);
     }
     liveness->initializeDef(getCurrentDef());
@@ -405,8 +405,9 @@ class CanonicalizeOSSALifetime final {
 
   void recordDebugValue(DebugValueInst *dvi) { debugValues.insert(dvi); }
 
-  void recordConsumingUse(Operand *use) {
-    consumingBlocks.insert(use->getUser()->getParent());
+  void recordConsumingUse(Operand *use) { recordConsumingUser(use->getUser()); }
+  void recordConsumingUser(SILInstruction *user) {
+    consumingBlocks.insert(user->getParent());
   }
   bool computeCanonicalLiveness();
 

lib/SILOptimizer/Utils/CanonicalizeOSSALifetime.cpp

@@ -68,6 +68,7 @@
 #include "swift/SILOptimizer/Utils/CanonicalizeOSSALifetime.h"
 #include "swift/SIL/InstructionUtils.h"
 #include "swift/SIL/NodeDatastructures.h"
+#include "swift/SIL/OSSALifetimeCompletion.h"
 #include "swift/SIL/OwnershipUtils.h"
 #include "swift/SIL/PrunedLiveness.h"
 #include "swift/SIL/Test.h"
@@ -249,6 +250,33 @@ void CanonicalizeOSSALifetime::extendLivenessToDeinitBarriers() {
   SmallVector<SILInstruction *, 4> outsideDestroys;
   findDestroysOutsideBoundary(outsideDestroys);
 
+  SmallVector<SILBasicBlock *, 32> discoveredBlocks(this->discoveredBlocks);
+  SSAPrunedLiveness completeLiveness(*liveness, &discoveredBlocks);
+
+  for (auto *end : outsideDestroys) {
+    completeLiveness.updateForUse(end, /*lifetimeEnding*/ true);
+  }
+
+  OSSALifetimeCompletion::visitUnreachableLifetimeEnds(
+      getCurrentDef(), completeLiveness, [&](auto *unreachable) {
+        recordConsumingUser(unreachable);
+        if (auto *previous = unreachable->getPreviousInstruction()) {
+          if (liveness->isInterestingUser(previous) ==
+              PrunedLiveness::IsInterestingUser::NonUser) {
+            liveness->updateForUse(previous, /*lifetimeEnding=*/false);
+          }
+          return;
+        }
+        for (auto *predecessor :
+             unreachable->getParent()->getPredecessorBlocks()) {
+          auto *previous = &predecessor->back();
+          if (liveness->isInterestingUser(previous) ==
+              PrunedLiveness::IsInterestingUser::NonUser) {
+            liveness->updateForUse(previous, /*lifetimeEnding=*/false);
+          }
+        }
+      });
+
   auto *def = getCurrentDef()->getDefiningInstruction();
   using InitialBlocks = ArrayRef<SILBasicBlock *>;
   auto *defBlock = getCurrentDef()->getParentBlock();

test/SILOptimizer/canonicalize_ossa_lifetime_unit.sil

@@ -181,18 +181,19 @@ entry(%instance : @owned $MoE):
   return %retval : $()
 }
 
-// CHECK-LABEL: begin running test 1 of 1 on respect_boundary_edges_when_extending_to_deinit_barriers: canonicalize-ossa-lifetime with: true, false, true, @argument
-// respect_boundary_edges_when_extending_to_deinit_barriers
+// CHECK-LABEL: begin running test 1 of 1 on respect_boundary_edges_when_extending_to_deinit_barriers
 // CHECK-LABEL: sil [ossa] @respect_boundary_edges_when_extending_to_deinit_barriers : {{.*}} {
 // CHECK:       bb0([[INSTANCE:%[^,]+]] :
 // CHECK:         apply {{%[^,]+}}()
 // CHECK:         cond_br undef, [[DIE:bb[0-9]+]], [[DESTROY:bb[0-9]+]]
 // CHECK:       [[DIE]]:
+// CHECK:         destroy_value [[INSTANCE]] : $C
 // CHECK:         unreachable
 // CHECK:       [[DESTROY]]:
 // CHECK:         destroy_value [[INSTANCE]] : $C
+// CHECK:         return
 // CHECK-LABEL: } // end sil function 'respect_boundary_edges_when_extending_to_deinit_barriers'
-// CHECK-LABEL: end running test 1 of 1 on respect_boundary_edges_when_extending_to_deinit_barriers: canonicalize-ossa-lifetime with: true, false, true, @argument
+// CHECK-LABEL: end running test 1 of 1 on respect_boundary_edges_when_extending_to_deinit_barriers
 sil [ossa] @respect_boundary_edges_when_extending_to_deinit_barriers : $@convention(thin) (@owned C) -> () {
 entry(%instance : @owned $C):
   test_specification "canonicalize-ossa-lifetime true false true @argument"
@@ -208,3 +209,36 @@ destroy:
   %retval = tuple ()
   return %retval : $()
 }
+
+// CHECK-LABEL: begin running test {{.*}} on respect_boundary_edges_when_extending_to_deinit_barriers_2
+// CHECK-LABEL: sil [ossa] @respect_boundary_edges_when_extending_to_deinit_barriers_2 : {{.*}} {
+// CHECK:       bb0([[INSTANCE:%[^,]+]] :
+// CHECK:         apply
+// CHECK:         cond_br undef, [[DIE:bb[0-9]+]], [[DESTROY:bb[0-9]+]]
+// CHECK:       [[DIE]]:
+// CHECK:         apply
+// CHECK:         destroy_value [[INSTANCE]]
+// CHECK:         unreachable
+// CHECK:       [[DESTROY]]:
+// CHECK:         destroy_value [[INSTANCE]]
+// CHECK-LABEL: } // end sil function 'respect_boundary_edges_when_extending_to_deinit_barriers_2'
+// CHECK-LABEL: end running test {{.*}} on respect_boundary_edges_when_extending_to_deinit_barriers_2
+sil [ossa] @respect_boundary_edges_when_extending_to_deinit_barriers_2 : $@convention(thin) (@owned C) -> () {
+entry(%instance : @owned $C):
+  test_specification "canonicalize-ossa-lifetime true false true @argument"
+  %barrier = function_ref @barrier : $@convention(thin) () -> ()
+  apply %barrier() : $@convention(thin) () -> ()
+  cond_br undef, die, destroy
+
+die:
+  apply %barrier() : $@convention(thin) () -> ()
+  br rlydie
+
+rlydie:
+  unreachable
+
+destroy:
+  destroy_value %instance : $C
+  %retval = tuple ()
+  return %retval : $()
+}

test/SILOptimizer/mem2reg_lifetime.sil

@@ -1858,7 +1858,8 @@ right:
 // CHECK:       {{bb[^,]+}}([[INSTANCE:%[^,]+]] : @owned $C):
 // CHECK:         cond_br undef, [[BB1:bb[0-9]+]], [[BB4:bb[0-9]+]]
 // CHECK:       [[BB1]]:
-// CHECK:         [[LIFETIME_OWNED:%[^,]+]] = move_value [lexical] [[INSTANCE]]
+// CHECK:         [[COPY:%[^,]+]] = copy_value [[INSTANCE]]
+// CHECK:         [[LIFETIME_OWNED:%[^,]+]] = move_value [lexical] [[COPY]]
 // CHECK:         cond_br undef, [[BB2:bb[0-9]+]], [[BB3:bb[0-9]+]]
 // CHECK:       [[BB2]]:
 // CHECK:         destroy_value [[LIFETIME_OWNED]]