Diagnose Infinite Recursion

include/swift/AST/DiagnosticsSIL.def

@@ -243,6 +243,8 @@ WARNING(unreachable_case,none,
 WARNING(switch_on_a_constant,none,
         "switch condition evaluates to a constant", ())
 NOTE(unreachable_code_note,none, "will never be executed", ())
+WARNING(warn_infinite_recursive_function,none,
+        "all paths through this function will call itself", ())
 
 // 'transparent' diagnostics
 ERROR(circular_transparent,none,

include/swift/SILOptimizer/PassManager/Passes.def

@@ -118,6 +118,8 @@ PASS(DefiniteInitialization, "definite-init",
      "Definite Initialization for Diagnostics")
 PASS(Devirtualizer, "devirtualizer",
      "Indirect Call Devirtualization")
+PASS(DiagnoseInfiniteRecursion, "diagnose-infinite-recursion",
+     "Diagnose Infinitely-Recursive Code")
 PASS(DiagnoseStaticExclusivity, "diagnose-static-exclusivity",
      "Static Enforcement of Law of Exclusivity")
 PASS(DiagnoseUnreachable, "diagnose-unreachable",

lib/SILOptimizer/Mandatory/CMakeLists.txt

@@ -6,6 +6,7 @@ set(MANDATORY_SOURCES
   Mandatory/DIMemoryUseCollector.cpp
   Mandatory/DIMemoryUseCollectorOwnership.cpp
   Mandatory/DataflowDiagnostics.cpp
+  Mandatory/DiagnoseInfiniteRecursion.cpp
   Mandatory/DiagnoseStaticExclusivity.cpp
   Mandatory/DiagnoseUnreachable.cpp
   Mandatory/GuaranteedARCOpts.cpp

lib/SILOptimizer/Mandatory/DiagnoseInfiniteRecursion.cpp

@@ -0,0 +1,163 @@
+//==-- DiagnoseInfiniteRecursion.cpp - Find infinitely-recursive applies --==//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements a diagnostic pass that detects deleterious forms of
+// recursive functions.
+//
+//===----------------------------------------------------------------------===//
+
+#define DEBUG_TYPE "infinite-recursion"
+#include "swift/AST/DiagnosticsSIL.h"
+#include "swift/AST/Expr.h"
+#include "swift/Parse/Lexer.h"
+#include "swift/SIL/CFG.h"
+#include "swift/SIL/SILArgument.h"
+#include "swift/SIL/SILInstruction.h"
+#include "swift/SILOptimizer/Analysis/PostOrderAnalysis.h"
+#include "swift/SILOptimizer/PassManager/Passes.h"
+#include "swift/SILOptimizer/PassManager/Transforms.h"
+#include "swift/SILOptimizer/Utils/Devirtualize.h"
+#include "llvm/ADT/PostOrderIterator.h"
+#include "llvm/ADT/iterator_range.h"
+#include "llvm/Support/Debug.h"
+
+using namespace swift;
+
+template<typename...T, typename...U>
+static void diagnose(ASTContext &Context, SourceLoc loc, Diag<T...> diag,
+                     U &&...args) {
+  Context.Diags.diagnose(loc,
+                         diag, std::forward<U>(args)...);
+}
+
+static bool hasRecursiveCallInPath(SILBasicBlock &Block,
+                                   SILFunction *Target,
+                                   ModuleDecl *TargetModule) {
+  // Process all instructions in the block to find applies that reference
+  // the parent function.  Also looks through vtables for statically
+  // dispatched (witness) methods.
+  for (auto &I : Block) {
+    auto *AI = dyn_cast<ApplyInst>(&I);
+    if (AI && AI->getCalleeFunction() && AI->getCalleeFunction() == Target)
+      return true;
+
+    if (FullApplySite FAI = FullApplySite::isa(&I)) {
+      // Don't touch dynamic dispatch.
+      if (isa<ObjCMethodInst>(FAI.getCallee()))
+        continue;
+
+      auto &M = FAI.getModule();
+      if (auto *CMI = dyn_cast<ClassMethodInst>(FAI.getCallee())) {
+        auto ClassType = CMI->getOperand()->getType();
+
+        // FIXME: If we're not inside the module context of the method,
+        // we may have to deserialize vtables.  If the serialized tables
+        // are damaged, the pass will crash.
+        //
+        // Though, this has the added bonus of not looking into vtables
+        // outside the current module.  Because we're not doing IPA, let
+        // alone cross-module IPA, this is all well and good.
+        auto *BGC = ClassType.getNominalOrBoundGenericNominal();
+        if (BGC && BGC->getModuleContext() != TargetModule) {
+          continue;
+        }
+
+        auto *F = getTargetClassMethod(M, ClassType, CMI);
+        if (F == Target)
+          return true;
+
+        continue;
+      }
+
+      if (auto *WMI = dyn_cast<WitnessMethodInst>(FAI.getCallee())) {
+        SILFunction *F;
+        SILWitnessTable *WT;
+
+        std::tie(F, WT) = M.lookUpFunctionInWitnessTable(
+            WMI->getConformance(), WMI->getMember());
+        if (F == Target)
+          return true;
+
+        continue;
+      }
+    }
+  }
+  return false;
+}
+
+static bool hasInfinitelyRecursiveApply(SILFunction &Fn,
+                                        SILFunction *TargetFn) {
+  SmallPtrSet<SILBasicBlock *, 16> Visited;
+  SmallVector<SILBasicBlock *, 16> WorkList;
+  // Keep track of whether we found at least one recursive path.
+  bool foundRecursion = false;
+
+  auto *TargetModule = TargetFn->getModule().getSwiftModule();
+  auto analyzeSuccessor = [&](SILBasicBlock *Succ) -> bool {
+    if (!Visited.insert(Succ).second)
+      return false;
+
+    // If the successor block contains a recursive call, end analysis there.
+    if (!hasRecursiveCallInPath(*Succ, TargetFn, TargetModule)) {
+      WorkList.push_back(Succ);
+      return false;
+    }
+    return true;
+  };
+
+  // Seed the work list with the entry block.
+  foundRecursion |= analyzeSuccessor(Fn.getEntryBlock());
+
+  while (!WorkList.empty()) {
+    SILBasicBlock *CurBlock = WorkList.pop_back_val();
+    // Found a path to the exit node without a recursive call.
+    if (CurBlock->getTerminator()->isFunctionExiting())
+      return false;
+
+    for (SILBasicBlock *Succ : CurBlock->getSuccessorBlocks())
+      foundRecursion |= analyzeSuccessor(Succ);
+  }
+  return foundRecursion;
+}
+
+namespace {
+  class DiagnoseInfiniteRecursion : public SILFunctionTransform {
+  public:
+    DiagnoseInfiniteRecursion() {}
+
+  private:
+    void run() override {
+      SILFunction *Fn = getFunction();
+      // Don't rerun diagnostics on deserialized functions.
+      if (Fn->wasDeserializedCanonical())
+        return;
+
+      // Ignore empty functions and straight-line thunks.
+      if (Fn->empty() || Fn->isThunk() != IsNotThunk)
+        return;
+
+      // If we can't diagnose it, there's no sense analyzing it.
+      if (!Fn->hasLocation() || Fn->getLocation().getSourceLoc().isInvalid())
+        return;
+
+      if (hasInfinitelyRecursiveApply(*Fn, Fn)) {
+        diagnose(Fn->getModule().getASTContext(),
+                 Fn->getLocation().getSourceLoc(),
+                 diag::warn_infinite_recursive_function);
+      }
+    }
+  };
+} // end anonymous namespace
+
+SILTransform *swift::createDiagnoseInfiniteRecursion() {
+  return new DiagnoseInfiniteRecursion();
+}

lib/SILOptimizer/PassManager/PassPipeline.cpp

@@ -98,6 +98,7 @@ static void addMandatoryOptPipeline(SILPassPipelinePlan &P,
   P.addDiagnosticConstantPropagation();
   P.addGuaranteedARCOpts();
   P.addDiagnoseUnreachable();
+  P.addDiagnoseInfiniteRecursion();
   P.addEmitDFDiagnostics();
   // Canonical swift requires all non cond_br critical edges to be split.
   P.addSplitNonCondBrCriticalEdges();

test/SILOptimizer/infinite_recursion.swift

@@ -0,0 +1,110 @@
+// RUN: %target-swift-frontend -emit-sil -primary-file %s -o /dev/null -verify
+
+func a() {  // expected-warning {{all paths through this function will call itself}}
+  a()
+}
+
+func b(_ x : Int) {  // expected-warning {{all paths through this function will call itself}}
+  if x != 0 {
+    b(x)
+  } else {
+    b(x+1)
+  }
+}
+
+func c(_ x : Int) {
+  if x != 0 {
+    c(5)
+  }
+}
+
+func d(_ x : Int) {  // expected-warning {{all paths through this function will call itself}}
+  var x = x
+  if x != 0 {
+    x += 1
+  }
+  return d(x)
+}
+
+// Doesn't warn on mutually recursive functions
+
+func e() { f() }
+func f() { e() }
+
+func g() { // expected-warning {{all paths through this function will call itself}}
+  while true { // expected-note {{condition always evaluates to true}}
+    g() 
+  }
+
+  g() // expected-warning {{will never be executed}}
+}
+
+func h(_ x : Int) {
+  while (x < 5) {
+    h(x+1)
+  }
+}
+
+func i(_ x : Int) {  // expected-warning {{all paths through this function will call itself}}
+  var x = x
+  while (x < 5) {
+    x -= 1
+  }
+  i(0)
+}
+
+func j() -> Int {  // expected-warning {{all paths through this function will call itself}}
+  return 5 + j()
+}
+
+func k() -> Any {  // expected-warning {{all paths through this function will call itself}}
+  return type(of: k())
+}
+
+class S {
+  convenience init(a: Int) { // expected-warning {{all paths through this function will call itself}}
+    self.init(a: a)
+  }
+  init(a: Int?) {}
+
+  static func a() { // expected-warning {{all paths through this function will call itself}}
+    return a()
+  }
+
+  func b() { // expected-warning {{all paths through this function will call itself}}
+    var i = 0
+    repeat {
+      i += 1
+      b()
+    } while (i > 5)
+  }
+}
+
+class T: S {
+  // No warning, calls super
+  override func b() {
+    var i = 0
+    repeat {
+      i += 1
+      super.b()
+    } while (i > 5)
+  }
+}
+
+func == (l: S?, r: S?) -> Bool { // expected-warning {{all paths through this function will call itself}}
+  if l == nil && r == nil { return true }
+  guard let l = l, let r = r else { return false }
+  return l === r
+}
+
+public func == <Element>(lhs: Array<Element>, rhs: Array<Element>) -> Bool { // expected-warning {{all paths through this function will call itself}}
+  return lhs == rhs
+}
+
+func factorial(_ n : UInt) -> UInt { // expected-warning {{all paths through this function will call itself}}
+  return (n != 0) ? factorial(n - 1) * n : factorial(1)
+}
+
+func tr(_ key: String) -> String { // expected-warning {{all paths through this function will call itself}}
+  return tr(key) ?? key // expected-warning {{left side of nil coalescing operator '??' has non-optional type}}
+}

test/SILOptimizer/infinite_recursion_objc.swift

@@ -0,0 +1,20 @@
+// RUN: %target-swift-frontend -emit-sil -primary-file %s -o /dev/null -verify
+
+// REQUIRES: objc_interop
+
+// A negative test that the infinite recursion pass doesn't diagnose dynamic
+// dispatch.
+
+import Foundation
+
+class MyRecursiveClass {
+  required init() {}
+  @objc dynamic func foo() {
+    return type(of: self).foo(self)()
+  }
+
+  @objc dynamic func foo2() {
+    return self.foo()
+  }
+}
+

test/SILOptimizer/unreachable_code.swift

@@ -215,7 +215,7 @@ class r20097963MyClass {
   }
 }
 
-func die() -> Never { die() }
+func die() -> Never { die() } // expected-warning {{all paths through this function will call itself}}
 
 func testGuard(_ a : Int) {
   guard case 4 = a else {  }  // expected-error {{'guard' body must not fall through, consider using a 'return' or 'throw'}}