Merge pull request #85005 from eeckstein/remove-copy-forwarding

Optimizer: remove the CopyForwarding pass

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/FunctionPasses/TempRValueElimination.swift

@@ -160,7 +160,11 @@ private func getRemovableAllocStackDestination(
   //   %x = load %allocStack   // looks like a load, but is a `load [take]`
   //   strong_release %x
   // ```
-  guard copy.parentFunction.hasOwnership || allocStack.isDestroyedOnAllPaths(context) else {
+  guard copy.parentFunction.hasOwnership ||
+        allocStack.isDestroyedOnAllPaths(context) ||
+        // We can easily remove a dead alloc_stack
+        allocStack.uses.ignore(user: copy).ignore(usersOfType: DeallocStackInst.self).isEmpty
+  else {
     return nil
   }
 
@@ -177,6 +181,10 @@ private func hoistDestroy(of allocStack: AllocStackInst, after lastUse: Instruct
   case let li as LoadInst where li.loadOwnership == .take:
     assert(li.address == allocStack, "load must be not take a projected address")
     return
+  case let apply as ApplyInst where apply.consumes(address: allocStack):
+    if allocStack.uses.contains(where: { $0.instruction == apply && apply.convention(of: $0)!.isGuaranteed }) {
+      return
+    }
   default:
     break
   }
@@ -266,6 +274,14 @@ private extension AllocStackInst {
   }
 }
 
+private extension ApplySite {
+  func consumes(address: Value) -> Bool {
+    argumentOperands.contains { argOp in
+      argOp.value == address && convention(of: argOp)!.isConsumed
+    }
+  }
+}
+
 /// Tries to move an `end_access` down to extend the access scope over all uses of the `alloc_stack`.
 /// For example:
 /// ```
@@ -531,13 +547,21 @@ private struct UseCollector : AddressDefUseWalker {
       uses.insert(copyFromStack)
       return .continueWalk
 
+    case is DebugValueInst:
+      return .continueWalk
+
     default:
       return .abortWalk
     }
   }
 
   private mutating func visitApply(address: Operand, apply: ApplySite) -> WalkResult {
-    if !apply.convention(of: address)!.isGuaranteed {
+    let argConvention = apply.convention(of: address)!
+    guard argConvention.isGuaranteed ||
+          // Only accept consuming-in arguments if it consumes the whole `alloc_stack`. A consume from
+          // a projection would destroy only a part of the `alloc_stack` and we don't handle this.
+          (argConvention == .indirectIn && (copy.isTakeOfSource && address.value == copy.destinationAddress))
+    else {
       return .abortWalk
     }
     uses.insert(apply)

include/swift/SILOptimizer/PassManager/Passes.def

@@ -254,8 +254,6 @@ LEGACY_PASS(ConstantEvaluatorTester, "test-constant-evaluator",
       "Test constant evaluator")
 LEGACY_PASS(ConstantEvaluableSubsetChecker, "test-constant-evaluable-subset",
      "Test Swift code snippets expected to be constant evaluable")
-LEGACY_PASS(CopyForwarding, "copy-forwarding",
-     "Copy Forwarding to Remove Redundant Copies")
 LEGACY_PASS(CopyPropagation, "copy-propagation",
      "Copy propagation to Remove Redundant SSA Copies, pruning debug info")
 LEGACY_PASS(MandatoryCopyPropagation, "mandatory-copy-propagation",

lib/SIL/Utils/InstructionUtils.cpp

@@ -841,7 +841,9 @@ RuntimeEffect swift::getRuntimeEffect(SILInstruction *inst, SILType &impactType)
       return RuntimeEffect::MetaData | RuntimeEffect::Releasing;
     if (!ca->isTakeOfSrc())
       return RuntimeEffect::MetaData | RuntimeEffect::RefCounting;
-    return RuntimeEffect::MetaData;
+    if (ca->getSrc()->getType().hasArchetype())
+      return RuntimeEffect::MetaData;
+    return RuntimeEffect::NoEffect;
   }
   case SILInstructionKind::TupleAddrConstructorInst: {
     auto *ca = cast<TupleAddrConstructorInst>(inst);

lib/SILOptimizer/PassManager/PassPipeline.cpp

@@ -459,12 +459,6 @@ void addFunctionPasses(SILPassPipelinePlan &P,
     P.addDestroyAddrHoisting();
   }
 
-  // Propagate copies through stack locations.  Should run after
-  // box-to-stack promotion since it is limited to propagating through
-  // stack locations. Should run before aggregate lowering since that
-  // splits up copy_addr.
-  P.addCopyForwarding();
-
   // This DCE pass is the only DCE on ownership SIL. It can cleanup OSSA related
   // dead code, e.g. left behind by the ObjCBridgingOptimization.
   P.addDCE();

lib/SILOptimizer/Transforms/CMakeLists.txt

@@ -9,7 +9,6 @@ target_sources(swiftSILOptimizer PRIVATE
   COWOpts.cpp
   CSE.cpp
   ConditionForwarding.cpp
-  CopyForwarding.cpp
   CopyPropagation.cpp
   DeadCodeElimination.cpp
   DeadObjectElimination.cpp