[OSSACanOwned] Don't dead-end extend if consumed.

When the utility is used by the ConsumeOperatorCopyableValuesChecker,
the checker guarantees that the lifetime can end at the consumes, that
there are no uses after those consumes.  In that circumstance, the
utility maintains liveness to those consumes and as far as possible
without introducing a copy everywhere else.

The lack of complete lifetimes has forced the utility to extend liveness
of values to dead-ends.  That extension, however, is in tension with the
use that the checker is putting the utility to.  If there is a dead-end
after a consume, liveness must not be maintained to that dead-end.

rdar://147586673

Author: nate-chandler

include/swift/SILOptimizer/Utils/CanonicalizeOSSALifetime.h

@@ -469,6 +469,12 @@ class CanonicalizeOSSALifetime final {
     return explicitLifetimeEnds.size() > 0;
   }
 
+  bool respectsDeadEnds() const {
+    // TODO: OSSALifetimeCompletion: Once lifetimes are always complete, delete
+    //                               this method.
+    return !endingLifetimeAtExplicitEnds();
+  }
+
   bool respectsDeinitBarriers() const {
     if (!currentDef->isLexical())
       return false;

lib/SILOptimizer/Utils/CanonicalizeOSSALifetime.cpp

@@ -1406,10 +1406,12 @@ bool CanonicalizeOSSALifetime::computeLiveness() {
     clear();
     return false;
   }
-  if (respectsDeinitBarriers()) {
-    extendLexicalLivenessToDeadEnds();
+  if (respectsDeadEnds()) {
+    if (respectsDeinitBarriers()) {
+      extendLexicalLivenessToDeadEnds();
+    }
+    extendLivenessToDeadEnds();
   }
-  extendLivenessToDeadEnds();
   if (respectsDeinitBarriers()) {
     extendLivenessToDeinitBarriers();
   }

test/Interpreter/consume_operator_kills_copyable_values.swift.gyb

@@ -176,6 +176,20 @@ func testNested2_${introducer}(_ c1: Bool, _ c2: Bool) {
   end([c1, c2])
 }
 
+// CHECK-LABEL: begin testDeadEnd_{{let|var}}(_:)(true)
+// CHECK:       hi
+// CHECK:       adios
+// CHECK:       barrier
+// CHECK-LABEL: end testDeadEnd_{{let|var}}(_:)(true)
+func testDeadEnd_${introducer}(_ condition: Bool) {
+  begin([condition])
+  ${introducer} x = X(0)
+  _ = consume x
+  guard condition else { fatalError() }
+  barrier()
+  end([condition])
+}
+
 func main_${introducer}() {
   simple_${introducer}()
   testLeft_${introducer}(true)
@@ -188,6 +202,7 @@ func main_${introducer}() {
   testNested2_${introducer}(false, true)
   testNested2_${introducer}(true, false)
   testNested2_${introducer}(true, true)
+  testDeadEnd_${introducer}(true)
 }
 
 % end