Merge pull request swiftlang#77806 from eeckstein/rle-of-array-elements

Optimizer: remove the ArrayElementPropagation optimization

Author: eeckstein

SwiftCompilerSources/Sources/Optimizer/Analysis/AliasAnalysis.swift

@@ -134,7 +134,7 @@ struct AliasAnalysis {
         if let apply = inst as? FullApplySite {
           // Workaround for quadratic complexity in ARCSequenceOpts.
           // We need to use an ever lower budget to not get into noticeable compile time troubles.
-          let effect = aa.getOwnershipEffect(of: apply, for: obj, path: path)
+          let effect = aa.getOwnershipEffect(of: apply, for: obj, path: path, complexityBudget: budget / 10)
           return effect.destroy
         }
         return obj.at(path).isEscaping(using: EscapesToInstructionVisitor(target: inst, isAddress: false),
@@ -421,10 +421,10 @@ struct AliasAnalysis {
   }
 
   private func getOwnershipEffect(of apply: FullApplySite, for value: Value,
-                                  path: SmallProjectionPath) -> SideEffects.Ownership {
+                                  path: SmallProjectionPath,
+                                  complexityBudget: Int) -> SideEffects.Ownership {
     let visitor = FullApplyEffectsVisitor(apply: apply, calleeAnalysis: context.calleeAnalysis, isAddress: false)
-    let budget = getComplexityBudget(for: apply.parentFunction)
-    if let result = value.at(path).visit(using: visitor, complexityBudget: budget, context) {
+    if let result = value.at(path).visit(using: visitor, complexityBudget: complexityBudget, context) {
       // The resulting effects are the argument effects to which `value` escapes to.
       return result.ownership
     } else {

SwiftCompilerSources/Sources/Optimizer/FunctionPasses/AllocVectorLowering.swift

@@ -227,7 +227,7 @@ private func createOutlinedGlobal(
   let elementType = allocVectorBuiltin.substitutionMap.replacementTypes[0]!
   let outlinedGlobal = context.createGlobalVariable(
         name: context.mangleOutlinedVariable(from: allocVectorBuiltin.parentFunction),
-        type: elementType, isPrivate: true)
+        type: elementType, linkage: .private, isLet: false)
 
   let globalBuilder = Builder(staticInitializerOf: outlinedGlobal, context)
 

SwiftCompilerSources/Sources/Optimizer/FunctionPasses/ObjectOutliner.swift

@@ -106,7 +106,10 @@ private func optimizeObjectAllocation(allocRef: AllocRefInstBase, _ context: Fun
 
   let outlinedGlobal = context.createGlobalVariable(
         name: context.mangleOutlinedVariable(from: allocRef.parentFunction),
-        type: allocRef.type, isPrivate: true)
+        type: allocRef.type, linkage: .private,
+        // Only if it's a COW object we can be sure that the object allocated in the global is not mutated.
+        // If someone wants to mutate it, it has to be copied first.
+        isLet: endOfInitInst is EndCOWMutationInst)
 
   constructObject(of: allocRef, inInitializerOf: outlinedGlobal, storesToClassFields, storesToTailElements, context)
   context.erase(instructions: storesToClassFields)
@@ -562,7 +565,7 @@ private func replace(findStringCall: ApplyInst,
 
   // Create an "opaque" global variable which is passed as inout to
   // _findStringSwitchCaseWithCache and into which the function stores the "cache".
-  let cacheVar = context.createGlobalVariable(name: name, type: cacheType, isPrivate: true)
+  let cacheVar = context.createGlobalVariable(name: name, type: cacheType, linkage: .private, isLet: false)
 
   let varBuilder = Builder(staticInitializerOf: cacheVar, context)
   let zero = varBuilder.createIntegerLiteral(0, type: wordTy)

SwiftCompilerSources/Sources/Optimizer/InstructionSimplification/SimplifyLoad.swift

@@ -234,12 +234,34 @@ private func getGlobalInitValue(address: Value, _ context: SimplifyContext) -> V
     }
   case let bai as BeginAccessInst:
     return getGlobalInitValue(address: bai.address, context)
+  case let rta as RefTailAddrInst:
+    return getGlobalTailElement(of: rta, index: 0)
+  case let ia as IndexAddrInst:
+    if let rta = ia.base as? RefTailAddrInst,
+       let literal = ia.index as? IntegerLiteralInst,
+       let index = literal.value
+    {
+      return getGlobalTailElement(of: rta, index: index)
+    }
+  case let rea as RefElementAddrInst:
+    if let object = rea.instance.immutableGlobalObjectRoot {
+      return object.baseOperands[rea.fieldIndex].value
+    }
   default:
     break
   }
   return nil
 }
 
+private func getGlobalTailElement(of refTailAddr: RefTailAddrInst, index: Int) -> Value? {
+  if let object = refTailAddr.instance.immutableGlobalObjectRoot,
+     index >= 0 && index < object.tailOperands.count
+  {
+    return object.tailOperands[index].value
+  }
+  return nil
+}
+
 private func getInitializerFromInitFunction(of globalAddr: GlobalAddrInst, _ context: SimplifyContext) -> Value? {
   guard let dependentOn = globalAddr.dependencyToken,
         let builtinOnce = dependentOn as? BuiltinInst,
@@ -321,6 +343,19 @@ private extension Value {
     }
     return (baseAddress: self, offset: 0)
   }
+
+  // If the reference-root of self references a global object, returns the `object` instruction of the
+  // global's initializer. But only if the global is a let-global.
+  var immutableGlobalObjectRoot: ObjectInst? {
+    if let gv = self.referenceRoot as? GlobalValueInst,
+       gv.global.isLet,
+       let initval = gv.global.staticInitValue,
+       let object = initval as? ObjectInst
+    {
+      return object
+    }
+    return nil
+  }
 }
 
 private extension Instruction {

SwiftCompilerSources/Sources/Optimizer/PassManager/Context.swift

@@ -391,9 +391,9 @@ struct FunctionPassContext : MutatingContext {
     }
   }
 
-  func createGlobalVariable(name: String, type: Type, isPrivate: Bool) -> GlobalVariable {
+  func createGlobalVariable(name: String, type: Type, linkage: Linkage, isLet: Bool) -> GlobalVariable {
     let gv = name._withBridgedStringRef {
-      _bridged.createGlobalVariable($0, type.bridged, isPrivate)
+      _bridged.createGlobalVariable($0, type.bridged, linkage.bridged, isLet)
     }
     return gv.globalVar
   }

SwiftCompilerSources/Sources/SIL/Utilities/WalkUtils.swift

@@ -689,7 +689,7 @@ extension ValueUseDefWalker {
       return walkUp(value: oer.existential, path: path.push(.existential, index: 0))
     case is BeginBorrowInst, is CopyValueInst, is MoveValueInst,
          is UpcastInst, is EndCOWMutationInst, is EndInitLetRefInst,
-         is BeginDeallocRefInst,
+         is BeginDeallocRefInst, is MarkDependenceInst,
          is RefToBridgeObjectInst, is BridgeObjectToRefInst, is MarkUnresolvedNonCopyableValueInst:
       return walkUp(value: (def as! Instruction).operands[0].value, path: path)
     case let urc as UncheckedRefCastInst:

include/swift/SILOptimizer/OptimizerBridging.h

@@ -255,7 +255,7 @@ struct BridgedPassContext {
                                                                BridgedFunction applySiteCallee) const;
 
   SWIFT_IMPORT_UNSAFE BridgedGlobalVar createGlobalVariable(BridgedStringRef name, BridgedType type,
-                                                            bool isPrivate) const;
+                                                            BridgedLinkage linkage, bool isLet) const;
   void inlineFunction(BridgedInstruction apply, bool mandatoryInline) const;
   SWIFT_IMPORT_UNSAFE BRIDGED_INLINE BridgedValue getSILUndef(BridgedType type) const;
   BRIDGED_INLINE bool optimizeMemoryAccesses(BridgedFunction f) const;

include/swift/SILOptimizer/PassManager/Passes.def

@@ -120,8 +120,6 @@ IRGEN_PASS(AllocStackHoisting, "alloc-stack-hoisting",
            "SIL alloc_stack Hoisting")
 PASS(ArrayCountPropagation, "array-count-propagation",
      "Array Count Propagation")
-PASS(ArrayElementPropagation, "array-element-propagation",
-     "Array Element Propagation")
 SWIFT_FUNCTION_PASS(AssumeSingleThreaded, "sil-assume-single-threaded",
      "Assume Single-Threaded Environment")
 SWIFT_MODULE_PASS(AsyncDemotion, "async-demotion",

lib/IRGen/GenDecl.cpp

@@ -2755,8 +2755,11 @@ Address IRGenModule::getAddrOfSILGlobalVariable(SILGlobalVariable *var,
   if (forDefinition && !gvar->hasInitializer()) {
     if (initVal) {
       gvar->setInitializer(initVal);
-      if (var->isLet() ||
-          (var->isInitializedObject() && canMakeStaticObjectReadOnly(var->getLoweredType()))) {
+      if (var->isLet() &&
+          // Even if it's a `let`, we cannot allocate an object as constant, because it's header
+          // (metadata, ref-count) is initialized at runtime.
+          // Exception: if it's an array for which we can initialize the header statically.
+          (!var->isInitializedObject() || canMakeStaticObjectReadOnly(var->getLoweredType()))) {
         gvar->setConstant(true);
       }
     } else {

lib/SILOptimizer/PassManager/PassManager.cpp

@@ -1879,11 +1879,14 @@ BridgedOwnedString BridgedPassContext::mangleWithClosureArgs(
   return BridgedOwnedString(mangler.mangle());
 }
 
-BridgedGlobalVar BridgedPassContext::createGlobalVariable(BridgedStringRef name, BridgedType type, bool isPrivate) const {
-  return {SILGlobalVariable::create(
+BridgedGlobalVar BridgedPassContext::createGlobalVariable(BridgedStringRef name, BridgedType type, BridgedLinkage linkage, bool isLet) const {
+  auto *global = SILGlobalVariable::create(
       *invocation->getPassManager()->getModule(),
-      isPrivate ? SILLinkage::Private : SILLinkage::Public, IsNotSerialized,
-      name.unbridged(), type.unbridged())};
+      (swift::SILLinkage)linkage, IsNotSerialized,
+      name.unbridged(), type.unbridged());
+  if (isLet)
+    global->setLet(true);
+  return {global};
 }
 
 void BridgedPassContext::fixStackNesting(BridgedFunction function) const {