Look through borrowed from instructions before calling lifetime completion

Lifetime completion will insert end_borrows only on borrow introducers.

Look through "borrowed from" instructions before calling it.

rdar://141490551

Author: meg-gupta

lib/SILOptimizer/Transforms/DeadCodeElimination.cpp

@@ -637,7 +637,7 @@ void DCE::endLifetimeOfLiveValue(Operand *op, SILInstruction *insertPt) {
   // If DCE is going to delete the block in which we have to insert a
   // compensating lifetime end, let complete lifetimes utility handle it.
   if (!LiveBlocks.contains(insertPt->getParent())) {
-    valuesToComplete.push_back(value);
+    valuesToComplete.push_back(lookThroughBorrowedFromDef(value));
     return;
   }
 

test/SILOptimizer/dead_code_elimination_nontrivial_ossa.sil

@@ -1376,3 +1376,38 @@ bb3:
   %res = tuple ()
   return %res : $()
 }
+
+// Ensure no verification error
+sil [ossa] @dce_borrowedfromuser : $@convention(thin) (@guaranteed FakeOptional<Klass>) -> () {
+bb0(%0 : @guaranteed $FakeOptional<Klass>):
+  %1 = copy_value %0
+  %2 = begin_borrow %1
+  %3 = begin_borrow %1
+  br bb1(%2, %3)
+
+bb1(%5 : @reborrow $FakeOptional<Klass>, %6 : @reborrow $FakeOptional<Klass>):
+  %7 = borrowed %6 from (%1)
+  %8 = borrowed %5 from (%1)
+  switch_enum %7, case #FakeOptional.some!enumelt: bb2, case #FakeOptional.none!enumelt: bb3
+
+bb2(%10 : @guaranteed $Klass):
+  %11 = function_ref @$use_klass2 : $@convention(thin) (@guaranteed Klass) -> ()
+  %12 = apply %11(%10) : $@convention(thin) (@guaranteed Klass) -> ()
+  br bb4
+
+bb3:
+  br bb4
+
+bb4:
+  br bb5(%8, %7)
+
+bb5(%16 : @reborrow $FakeOptional<Klass>, %17 : @reborrow $FakeOptional<Klass>):
+  %18 = borrowed %17 from (%1)
+  %19 = borrowed %16 from (%1)
+  end_borrow %19
+  end_borrow %18
+  destroy_value %1
+  %23 = tuple ()
+  return %23
+}
+