MoveOnlyAddressChecker: More robust checking for consume-during-borrow.

- While an opaque borrow access occurs to part of a value, the entire scope of
  the access needs to be treated as a liveness range, so add the `EndAccess`es
  to the liveness range.
- The SIL verifier may crash the compiler on SILGen-generated code when the
  developer's source contains consume-during-borrow code patterns. Allow
  `load_borrow` instructions to be marked `[unchecked]`, which suppresses
  verifier checks until the move checker runs and gets a chance to properly
  diagnose these errors.

Fixes rdar://124360175.

Author: jckarter

include/swift/SIL/SILInstruction.h

@@ -4591,14 +4591,29 @@ class StoreInst
 /// instruction in its use-def list.
 class LoadBorrowInst :
     public UnaryInstructionBase<SILInstructionKind::LoadBorrowInst,
-                                SingleValueInstruction> {
+                                SingleValueInstruction>
+{
   friend class SILBuilder;
 
+  bool Unchecked = false;
+
 public:
   LoadBorrowInst(SILDebugLocation DebugLoc, SILValue LValue)
       : UnaryInstructionBase(DebugLoc, LValue,
                              LValue->getType().getObjectType()) {}
 
+  // True if the invariants on `load_borrow` have not been checked and
+  // should not be strictly enforced.
+  //
+  // This can only occur during raw SIL before move-only checking occurs.
+  // Developers can write incorrect code using noncopyable types that
+  // consumes or mutates a memory location while that location is borrowed,
+  // but the move-only checker must diagnose those problems before canonical
+  // SIL is formed.
+  bool isUnchecked() const { return Unchecked; }
+  
+  void setUnchecked(bool value) { Unchecked = value; }
+
   using EndBorrowRange =
       decltype(std::declval<ValueBase>().getUsersOfType<EndBorrowInst>());
 

lib/SIL/IR/SILPrinter.cpp

@@ -1733,6 +1733,9 @@ class SILPrinter : public SILInstructionVisitor<SILPrinter> {
   }
 
   void visitLoadBorrowInst(LoadBorrowInst *LBI) {
+    if (LBI->isUnchecked()) {
+      *this << "[unchecked] ";
+    }
     *this << getIDAndType(LBI->getOperand());
   }
 

lib/SIL/Parser/ParseSIL.cpp

@@ -3733,12 +3733,28 @@ bool SILParser::parseSpecificSILInstruction(SILBuilder &B,
 
   case SILInstructionKind::LoadBorrowInst: {
     SourceLoc AddrLoc;
+    
+    bool IsUnchecked = false;
+    StringRef AttrName;
+    SourceLoc AttrLoc;
+    if (parseSILOptional(AttrName, AttrLoc, *this)) {
+      if (AttrName == "unchecked") {
+        IsUnchecked = true;
+      } else {
+        P.diagnose(InstLoc.getSourceLoc(),
+                   diag::sil_invalid_attribute_for_instruction, AttrName,
+                   "load_borrow");
+        return true;
+      }
+    }
 
     if (parseTypedValueRef(Val, AddrLoc, B) ||
         parseSILDebugLocation(InstLoc, B))
       return true;
 
-    ResultVal = B.createLoadBorrow(InstLoc, Val);
+    auto LB = B.createLoadBorrow(InstLoc, Val);
+    LB->setUnchecked(IsUnchecked);
+    ResultVal = LB;
     break;
   }
 

lib/SIL/Verifier/MemoryLifetimeVerifier.cpp

@@ -788,7 +788,9 @@ void MemoryLifetimeVerifier::checkBlock(SILBasicBlock *block, Bits &bits) {
           requireBitsSet(bits, sbi->getDest(), &I);
           locations.clearBits(bits, sbi->getDest());
         } else if (auto *lbi = dyn_cast<LoadBorrowInst>(ebi->getOperand())) {
-          requireBitsSet(bits, lbi->getOperand(), &I);
+          if (!lbi->isUnchecked()) {
+            requireBitsSet(bits, lbi->getOperand(), &I);
+          }
         }
         break;
       }

lib/SIL/Verifier/SILVerifier.cpp

@@ -2623,8 +2623,13 @@ class SILVerifier : public SILVerifierBase<SILVerifier> {
     requireSameType(LBI->getOperand()->getType().getObjectType(),
                     LBI->getType(),
                     "Load operand type and result type mismatch");
-    require(loadBorrowImmutabilityAnalysis.isImmutable(LBI),
-            "Found load borrow that is invalidated by a local write?!");
+    if (LBI->isUnchecked()) {
+      require(LBI->getModule().getStage() == SILStage::Raw,
+              "load_borrow can only be [unchecked] in raw SIL");
+    } else {
+      require(loadBorrowImmutabilityAnalysis.isImmutable(LBI),
+              "Found load borrow that is invalidated by a local write?!");
+    }
   }
 
   void checkBeginBorrowInst(BeginBorrowInst *bbi) {

lib/SILGen/SILGenLValue.cpp

@@ -1231,6 +1231,11 @@ namespace {
         return base;
       }
       auto result = SGF.B.createLoadBorrow(loc, base.getValue());
+      // Mark the load_borrow as unchecked. We can't stop the source code from
+      // trying to mutate or consume the same lvalue during this borrow, so
+      // we don't want verifiers to trip before the move checker gets a chance
+      // to diagnose these situations.
+      result->setUnchecked(true);
       return SGF.emitFormalEvaluationManagedBorrowedRValueWithCleanup(loc,
          base.getValue(), result);
     }

lib/SILOptimizer/Mandatory/MoveOnlyAddressCheckerUtils.cpp

@@ -1258,23 +1258,29 @@ void UseState::initializeLiveness(
                             << *livenessInstAndValue.first;
                liveness.print(llvm::dbgs()));
   }
+  
+  auto updateForLivenessAccess = [&](BeginAccessInst *beginAccess,
+                                     const SmallBitVector &livenessMask) {
+    for (auto *endAccess : beginAccess->getEndAccesses()) {
+      liveness.updateForUse(endAccess, livenessMask, false /*lifetime ending*/);
+    }
+  };
 
   for (auto livenessInstAndValue : nonconsumingUses) {
     if (auto *lbi = dyn_cast<LoadBorrowInst>(livenessInstAndValue.first)) {
       auto accessPathWithBase =
           AccessPathWithBase::computeInScope(lbi->getOperand());
       if (auto *beginAccess =
               dyn_cast_or_null<BeginAccessInst>(accessPathWithBase.base)) {
-        for (auto *endAccess : beginAccess->getEndAccesses()) {
-          liveness.updateForUse(endAccess, livenessInstAndValue.second,
-                                false /*lifetime ending*/);
-        }
+        updateForLivenessAccess(beginAccess, livenessInstAndValue.second);
       } else {
         for (auto *ebi : lbi->getEndBorrows()) {
           liveness.updateForUse(ebi, livenessInstAndValue.second,
                                 false /*lifetime ending*/);
         }
       }
+    } else if (auto *bai = dyn_cast<BeginAccessInst>(livenessInstAndValue.first)) {
+      updateForLivenessAccess(bai, livenessInstAndValue.second);
     } else {
       liveness.updateForUse(livenessInstAndValue.first,
                             livenessInstAndValue.second,

lib/SILOptimizer/Mandatory/MoveOnlyChecker.cpp

@@ -214,6 +214,22 @@ void MoveOnlyChecker::checkAddresses() {
 
 namespace {
 
+static bool canonicalizeLoadBorrows(SILFunction *F) {
+  bool changed = false;
+  for (auto &block : *F) {
+    for (auto &inst : block) {
+      if (auto *lbi = dyn_cast<LoadBorrowInst>(&inst)) {
+        if (lbi->isUnchecked()) {
+          changed = true;
+          lbi->setUnchecked(false);
+        }
+      }
+    }
+  }
+  
+  return changed;
+}
+
 class MoveOnlyCheckerPass : public SILFunctionTransform {
   void run() override {
     auto *fn = getFunction();
@@ -228,8 +244,11 @@ class MoveOnlyCheckerPass : public SILFunctionTransform {
     // If an earlier pass told use to not emit diagnostics for this function,
     // clean up any copies, invalidate the analysis, and return early.
     if (fn->hasSemanticsAttr(semantics::NO_MOVEONLY_DIAGNOSTICS)) {
-      if (cleanupNonCopyableCopiesAfterEmittingDiagnostic(getFunction()))
+      bool didChange = canonicalizeLoadBorrows(fn);
+      didChange |= cleanupNonCopyableCopiesAfterEmittingDiagnostic(getFunction());
+      if (didChange) {
         invalidateAnalysis(SILAnalysis::InvalidationKind::Instructions);
+      }
       return;
     }
 
@@ -252,6 +271,11 @@ class MoveOnlyCheckerPass : public SILFunctionTransform {
                                                    checker.diagnosticEmitter);
     }
 
+    // Remaining borrows
+    // should be correctly immutable. We can canonicalize any remaining
+    // `load_borrow [unchecked]` instructions.
+    checker.madeChange |= canonicalizeLoadBorrows(fn);
+
     checker.madeChange |=
         cleanupNonCopyableCopiesAfterEmittingDiagnostic(fn);
 

lib/Serialization/DeserializeSIL.cpp

@@ -2260,7 +2260,6 @@ bool SILDeserializer::readSILInstruction(SILFunction *Fn,
   UNARY_INSTRUCTION(EndLifetime)
   UNARY_INSTRUCTION(ExtendLifetime)
   UNARY_INSTRUCTION(CopyBlock)
-  UNARY_INSTRUCTION(LoadBorrow)
   UNARY_INSTRUCTION(EndInitLetRef)
   REFCOUNTING_INSTRUCTION(StrongRetain)
   REFCOUNTING_INSTRUCTION(StrongRelease)
@@ -2271,6 +2270,17 @@ bool SILDeserializer::readSILInstruction(SILFunction *Fn,
 #undef UNARY_INSTRUCTION
 #undef REFCOUNTING_INSTRUCTION
 
+  case SILInstructionKind::LoadBorrowInst: {
+    assert(RecordKind == SIL_ONE_OPERAND && "Layout should be OneOperand.");
+    auto LB = Builder.createLoadBorrow(
+        Loc, getLocalValue(Builder.maybeGetFunction(), ValID,
+                           getSILType(MF->getType(TyID),
+                                      (SILValueCategory)TyCategory, Fn)));
+    LB->setUnchecked(Attr != 0);
+    ResultInst = LB;
+    break;
+  }
+
   case SILInstructionKind::BeginBorrowInst: {
     assert(RecordKind == SIL_ONE_OPERAND && "Layout should be OneOperand.");
     auto isLexical = IsLexical_t(Attr & 0x1);

lib/Serialization/SerializeSIL.cpp

@@ -1601,6 +1601,8 @@ void SILSerializer::writeSILInstruction(const SILInstruction &SI) {
     } else if (auto *I = dyn_cast<CopyableToMoveOnlyWrapperValueInst>(&SI)) {
       Attr = I->getForwardingOwnershipKind() == OwnershipKind::Owned ? true
                                                                      : false;
+    } else if (auto *LB = dyn_cast<LoadBorrowInst>(&SI)) {
+      Attr = LB->isUnchecked();
     }
     writeOneOperandLayout(SI.getKind(), Attr, SI.getOperand(0));
     break;