[CanOSSALife] Respect barrier boundary edges.

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

Previously, barrier edges did not result in any additions to liveness on
the theory that they would be rediscovered.  This is not always true (as
in the case of dead defs).

Here, each barrier edge different from the def block results in
additions to liveness.  Specifically, it results in the back of the
single predecessor being added to liveness.

rdar://115410893

Author: nate-chandler

lib/SILOptimizer/Utils/CanonicalizeOSSALifetime.cpp

@@ -286,9 +286,17 @@ void CanonicalizeOSSALifetime::extendLivenessToDeinitBarriers() {
                              /*lifetimeEnding*/ false);
     }
   }
-  // Ignore barriers.edges.  The beginning of the targets of such edges should
-  // not be added to liveness.  These edges will be rediscovered when computing
-  // the liveness boundary.
+  for (auto *edge : barriers.edges) {
+    if (edge == getCurrentDef()->getParentBlock()) {
+      // A destroy should be inserted at the begin of this block, but that does
+      // not require adding any instructions to liveness.
+      continue;
+    }
+    auto *predecessor = edge->getSinglePredecessorBlock();
+    assert(predecessor);
+    liveness->updateForUse(&predecessor->back(),
+                           /*lifetimeEnding*/ false);
+  }
 }
 
 // Return true if \p inst is an end_access whose access scope overlaps the end

test/SILOptimizer/canonicalize_ossa_lifetime_unit.sil

@@ -180,3 +180,31 @@ entry(%instance : @owned $MoE):
   %retval = tuple ()
   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: 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:         unreachable
+// CHECK:       [[DESTROY]]:
+// CHECK:         destroy_value [[INSTANCE]] : $C
+// 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
+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"
+  %barrier = function_ref @barrier : $@convention(thin) () -> ()
+  apply %barrier() : $@convention(thin) () -> ()
+  cond_br undef, die, destroy
+
+die:
+  unreachable
+
+destroy:
+  destroy_value %instance : $C
+  %retval = tuple ()
+  return %retval : $()
+}