[OSSACanOwned] Dead-end extend base lifetime.

Regardless of consumes of copies, if the original value is not consumed
on a dead-end path, it must remain life to that dead-end.

rdar://145154549

Author: nate-chandler

include/swift/SILOptimizer/Utils/CanonicalizeOSSALifetime.h

@@ -237,6 +237,8 @@ class CanonicalizeOSSALifetime final {
   /// copies.
   const MaximizeLifetime_t maximizeLifetime;
 
+  SILFunction *function;
+
   // If present, will be used to ensure that the lifetime is not shortened to
   // end inside an access scope which it previously enclosed.  (Note that ending
   // before such an access scope is fine regardless.)
@@ -354,7 +356,7 @@ class CanonicalizeOSSALifetime final {
       DeadEndBlocksAnalysis *deadEndBlocksAnalysis, DominanceInfo *domTree,
       BasicCalleeAnalysis *calleeAnalysis, InstructionDeleter &deleter)
       : pruneDebugMode(pruneDebugMode), maximizeLifetime(maximizeLifetime),
-        accessBlockAnalysis(accessBlockAnalysis),
+        function(function), accessBlockAnalysis(accessBlockAnalysis),
         deadEndBlocksAnalysis(deadEndBlocksAnalysis), domTree(domTree),
         calleeAnalysis(calleeAnalysis), deleter(deleter) {}
 

lib/SILOptimizer/Utils/CanonicalizeOSSALifetime.cpp

@@ -277,6 +277,25 @@ bool CanonicalizeOSSALifetime::computeCanonicalLiveness() {
 void CanonicalizeOSSALifetime::extendLivenessToDeadEnds() {
   // TODO: OSSALifetimeCompletion: Once lifetimes are always complete, delete
   //                               this method.
+
+  // (1) Extend liveness to the availability boundary of currentDef.
+  SmallVector<SILBasicBlock *, 32> directDiscoverdBlocks;
+  SSAPrunedLiveness directLiveness(function, &directDiscoverdBlocks);
+  directLiveness.initializeDef(getCurrentDef());
+  directLiveness.computeSimple();
+  OSSALifetimeCompletion::visitAvailabilityBoundary(
+      getCurrentDef(), directLiveness, [&](auto *unreachable, auto end) {
+        if (end == OSSALifetimeCompletion::LifetimeEnd::Boundary) {
+          recordUnreachableLifetimeEnd(unreachable);
+        }
+        unreachable->visitPriorInstructions([&](auto *inst) {
+          liveness->extendToNonUse(inst);
+          return true;
+        });
+      });
+
+  // (2) Extend liveness to the availability boundary of the copy-extended
+  //     availability boundary of currentDef.
   SmallVector<SILBasicBlock *, 32> discoveredBlocks(this->discoveredBlocks);
   SSAPrunedLiveness completeLiveness(*liveness, &discoveredBlocks);
 

test/SILOptimizer/canonicalize_ossa_lifetime_unit.sil

@@ -3,6 +3,9 @@
 import Swift
 
 class C {}
+
+enum Never {}
+sil @run : $@convention(thin) () -> Never
 sil @getOwned : $@convention(thin) () -> @owned C
 sil @barrier : $@convention(thin) () -> ()
 sil [ossa] @getC : $@convention(thin) () -> @owned C
@@ -918,3 +921,18 @@ entry(%a: @owned $C):
   %retval = tuple ()
   return %retval
 }
+
+// CHECK-LABEL: begin running test {{.*}} on extend_lifetime_to_deadend_despite_copy_consume
+// CHECK-LABEL: sil [ossa] @extend_lifetime_to_deadend_despite_copy_consume : {{.*}} {
+// CHECK      :   copy_value
+// CHECK-LABEL: } // end sil function 'extend_lifetime_to_deadend_despite_copy_consume'
+// CHECK-LABEL: end running test {{.*}} on extend_lifetime_to_deadend_despite_copy_consume
+sil [ossa] @extend_lifetime_to_deadend_despite_copy_consume : $@convention(thin) (@owned C) -> () {
+entry(%c : @owned $C):
+  specify_test "canonicalize_ossa_lifetime true false true @argument"
+  %cc = copy_value %c
+  %takeC = function_ref @takeC : $@convention(thin) (@owned C) -> ()
+  apply %takeC(%cc) : $@convention(thin) (@owned C) -> ()
+  %run = function_ref @run : $@convention(thin) () -> Never
+  unreachable
+}