[semantic-arc-opts] Eliminate all dead live ranges.

Previously, we only did single copy/destroys. Now we handle a copy + any number
of destroy_values.

Author: gottesmm

lib/SILOptimizer/Mandatory/SemanticARCOpts.cpp

@@ -181,9 +181,10 @@ static bool performGuaranteedCopyValueOptimization(CopyValueInst *cvi) {
   return true;
 }
 
-bool SemanticARCOptVisitor::visitCopyValueInst(CopyValueInst *cvi) {
-  // If our copy value inst has a single destroy value user, eliminate
-  // it.
+/// If cvi only has destroy value users, then cvi is a dead live range. Lets
+/// eliminate all such dead live ranges.
+static bool eliminateDeadLiveRangeCopyValue(CopyValueInst *cvi) {
+  // See if we are lucky and have a simple case.
   if (auto *op = cvi->getSingleUse()) {
     if (auto *dvi = dyn_cast<DestroyValueInst>(op->getUser())) {
       dvi->eraseFromParent();
@@ -193,6 +194,38 @@ bool SemanticARCOptVisitor::visitCopyValueInst(CopyValueInst *cvi) {
     }
   }
 
+  // If all of our copy_value users are destroy_value, zap all of the
+  // instructions. We begin by performing that check and gathering up our
+  // destroy_value.
+  SmallVector<DestroyValueInst *, 16> destroys;
+  if (!all_of(cvi->getUses(), [&](Operand *op) {
+        auto *dvi = dyn_cast<DestroyValueInst>(op->getUser());
+        if (!dvi)
+          return false;
+
+        // Stash dvi in destroys so we can easily eliminate it later.
+        destroys.push_back(dvi);
+        return true;
+      })) {
+    return false;
+  }
+
+  // Now that we have a truly dead live range copy value, eliminate it!
+  while (!destroys.empty()) {
+    destroys.pop_back_val()->eraseFromParent();
+    ++NumEliminatedInsts;
+  }
+  cvi->eraseFromParent();
+  ++NumEliminatedInsts;
+  return true;
+}
+
+bool SemanticARCOptVisitor::visitCopyValueInst(CopyValueInst *cvi) {
+  // If our copy value inst has only destroy_value users, it is a dead live
+  // range. Try to eliminate them.
+  if (eliminateDeadLiveRangeCopyValue(cvi))
+    return true;
+
   // Then try to perform the guaranteed copy value optimization.
   if (performGuaranteedCopyValueOptimization(cvi))
     return true;

test/SILOptimizer/semantic-arc-opts.sil

@@ -9,6 +9,7 @@ import Builtin
 //////////////////
 
 sil @guaranteed_user : $@convention(thin) (@guaranteed Builtin.NativeObject) -> ()
+sil @owned_user : $@convention(thin) (@owned Builtin.NativeObject) -> ()
 
 struct NativeObjectPair {
   var obj1 : Builtin.NativeObject
@@ -188,3 +189,53 @@ bb0(%0 : @unowned $Builtin.NativeObject):
   %9999 = tuple()
   return %9999 : $()
 }
+
+// CHECK-LABEL: sil @dead_live_range_multiple_destroy_value : $@convention(thin) (@owned Builtin.NativeObject) -> () {
+// CHECK-NOT: copy_value
+// CHECK-NOT: destroy_value
+// CHECK: bb3:
+// CHECK:     destroy_value
+// CHECK: } // end sil function 'dead_live_range_multiple_destroy_value'
+sil @dead_live_range_multiple_destroy_value : $@convention(thin) (@owned Builtin.NativeObject) -> () {
+bb0(%0 : @owned $Builtin.NativeObject) :
+  %1 = copy_value %0 : $Builtin.NativeObject
+  cond_br undef, bb1, bb2
+
+bb1:
+  destroy_value %1 : $Builtin.NativeObject
+  br bb3
+
+bb2:
+  destroy_value %1 : $Builtin.NativeObject
+  br bb3
+
+bb3:
+  destroy_value %0 : $Builtin.NativeObject
+  %9999 = tuple()
+  return %9999 : $()
+}
+
+// CHECK-LABEL: sil @dead_live_range_multiple_destroy_value_consuming_user : $@convention(thin) (@owned Builtin.NativeObject) -> () {
+// CHECK: copy_value
+// CHECK: destroy_value
+// CHECK: destroy_value
+// CHECK: } // end sil function 'dead_live_range_multiple_destroy_value_consuming_user'
+sil @dead_live_range_multiple_destroy_value_consuming_user : $@convention(thin) (@owned Builtin.NativeObject) -> () {
+bb0(%0 : @owned $Builtin.NativeObject) :
+  %1 = copy_value %0 : $Builtin.NativeObject
+  cond_br undef, bb1, bb2
+
+bb1:
+  destroy_value %1 : $Builtin.NativeObject
+  br bb3
+
+bb2:
+  %2 = function_ref @owned_user : $@convention(thin) (@owned Builtin.NativeObject) -> ()
+  apply %2(%1) : $@convention(thin) (@owned Builtin.NativeObject) -> ()
+  br bb3
+
+bb3:
+  destroy_value %0 : $Builtin.NativeObject
+  %9999 = tuple()
+  return %9999 : $()
+}