[IR] Disallow recursive types (llvm#114799)

StructType::setBody is the only mechanism that can potentially create
recursion in the type system. Add a runtime check that it is not
actually used to create recursion.

If the check fails, report an error from LLParser, BitcodeReader and
IRLinker. In all other cases assert that the check succeeds.

In future StructType::setBody will be removed in favor of specifying the
body when the type is created, so any performance hit from this runtime
check will be temporary.

Author: jayfoad

llvm/docs/LangRef.rst

@@ -4386,7 +4386,7 @@ is defined inline with other types (e.g. ``[2 x {i32, i32}]``) whereas
 identified types are always defined at the top level with a name.
 Literal types are uniqued by their contents and can never be recursive
 or opaque since there is no way to write one. Identified types can be
-recursive, can be opaqued, and are never uniqued.
+opaqued and are never uniqued. Identified types must not be recursive.
 
 :Syntax:
 

llvm/docs/ReleaseNotes.md

@@ -56,6 +56,8 @@ Makes programs 10x faster by doing Special New Thing.
 Changes to the LLVM IR
 ----------------------
 
+* Types are no longer allowed to be recursive.
+
 * The `x86_mmx` IR type has been removed. It will be translated to
   the standard vector type `<1 x i64>` in bitcode upgrade.
 * Renamed `llvm.experimental.stepvector` intrinsic to `llvm.stepvector`.

llvm/include/llvm/IR/DerivedTypes.h

@@ -33,6 +33,7 @@ class Value;
 class APInt;
 class LLVMContext;
 template <typename T> class Expected;
+class Error;
 
 /// Class to represent integer types. Note that this class is also used to
 /// represent the built-in integer types: Int1Ty, Int8Ty, Int16Ty, Int32Ty and
@@ -317,9 +318,18 @@ class StructType : public Type {
   /// suffix if there is a collision. Do not call this on an literal type.
   void setName(StringRef Name);
 
-  /// Specify a body for an opaque identified type.
+  /// Specify a body for an opaque identified type, which must not make the type
+  /// recursive.
   void setBody(ArrayRef<Type*> Elements, bool isPacked = false);
 
+  /// Specify a body for an opaque identified type or return an error if it
+  /// would make the type recursive.
+  Error setBodyOrError(ArrayRef<Type *> Elements, bool isPacked = false);
+
+  /// Return an error if the body for an opaque identified type would make it
+  /// recursive.
+  Error checkBody(ArrayRef<Type *> Elements);
+
   template <typename... Tys>
   std::enable_if_t<are_base_of<Type, Tys...>::value, void>
   setBody(Type *elt1, Tys *... elts) {

llvm/lib/AsmParser/LLParser.cpp

@@ -3391,7 +3391,9 @@ bool LLParser::parseStructDefinition(SMLoc TypeLoc, StringRef Name,
       (isPacked && parseToken(lltok::greater, "expected '>' in packed struct")))
     return true;
 
-  STy->setBody(Body, isPacked);
+  if (auto E = STy->setBodyOrError(Body, isPacked))
+    return tokError(toString(std::move(E)));
+
   ResultTy = STy;
   return false;
 }

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -2659,7 +2659,8 @@ Error BitcodeReader::parseTypeTableBody() {
       }
       if (EltTys.size() != Record.size()-1)
         return error("Invalid named struct record");
-      Res->setBody(EltTys, Record[0]);
+      if (auto E = Res->setBodyOrError(EltTys, Record[0]))
+        return E;
       ContainedIDs.append(Record.begin() + 1, Record.end());
       ResultTy = Res;
       break;

llvm/lib/IR/Type.cpp

@@ -13,6 +13,7 @@
 #include "llvm/IR/Type.h"
 #include "LLVMContextImpl.h"
 #include "llvm/ADT/APInt.h"
+#include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
@@ -436,20 +437,37 @@ bool StructType::containsHomogeneousTypes() const {
 }
 
 void StructType::setBody(ArrayRef<Type*> Elements, bool isPacked) {
+  cantFail(setBodyOrError(Elements, isPacked));
+}
+
+Error StructType::setBodyOrError(ArrayRef<Type *> Elements, bool isPacked) {
   assert(isOpaque() && "Struct body already set!");
 
+  if (auto E = checkBody(Elements))
+    return E;
+
   setSubclassData(getSubclassData() | SCDB_HasBody);
   if (isPacked)
     setSubclassData(getSubclassData() | SCDB_Packed);
 
   NumContainedTys = Elements.size();
+  ContainedTys = Elements.empty()
+                     ? nullptr
+                     : Elements.copy(getContext().pImpl->Alloc).data();
 
-  if (Elements.empty()) {
-    ContainedTys = nullptr;
-    return;
-  }
+  return Error::success();
+}
 
-  ContainedTys = Elements.copy(getContext().pImpl->Alloc).data();
+Error StructType::checkBody(ArrayRef<Type *> Elements) {
+  SmallSetVector<Type *, 4> Worklist(Elements.begin(), Elements.end());
+  for (unsigned I = 0; I < Worklist.size(); ++I) {
+    Type *Ty = Worklist[I];
+    if (Ty == this)
+      return createStringError(Twine("identified structure type '") +
+                               getName() + "' is recursive");
+    Worklist.insert(Ty->subtype_begin(), Ty->subtype_end());
+  }
+  return Error::success();
 }
 
 void StructType::setName(StringRef Name) {

llvm/lib/Linker/IRMover.cpp

@@ -34,6 +34,12 @@
 #include <utility>
 using namespace llvm;
 
+/// Most of the errors produced by this module are inconvertible StringErrors.
+/// This convenience function lets us return one of those more easily.
+static Error stringErr(const Twine &T) {
+  return make_error<StringError>(T, inconvertibleErrorCode());
+}
+
 //===----------------------------------------------------------------------===//
 // TypeMap implementation.
 //===----------------------------------------------------------------------===//
@@ -69,7 +75,7 @@ class TypeMapTy : public ValueMapTypeRemapper {
 
   /// Produce a body for an opaque type in the dest module from a type
   /// definition in the source module.
-  void linkDefinedTypeBodies();
+  Error linkDefinedTypeBodies();
 
   /// Return the mapped type to use for the specified input type from the
   /// source module.
@@ -207,7 +213,7 @@ bool TypeMapTy::areTypesIsomorphic(Type *DstTy, Type *SrcTy) {
   return true;
 }
 
-void TypeMapTy::linkDefinedTypeBodies() {
+Error TypeMapTy::linkDefinedTypeBodies() {
   SmallVector<Type *, 16> Elements;
   for (StructType *SrcSTy : SrcDefinitionsToResolve) {
     StructType *DstSTy = cast<StructType>(MappedTypes[SrcSTy]);
@@ -218,11 +224,13 @@ void TypeMapTy::linkDefinedTypeBodies() {
     for (unsigned I = 0, E = Elements.size(); I != E; ++I)
       Elements[I] = get(SrcSTy->getElementType(I));
 
-    DstSTy->setBody(Elements, SrcSTy->isPacked());
+    if (auto E = DstSTy->setBodyOrError(Elements, SrcSTy->isPacked()))
+      return E;
     DstStructTypesSet.switchToNonOpaque(DstSTy);
   }
   SrcDefinitionsToResolve.clear();
   DstResolvedOpaqueTypes.clear();
+  return Error::success();
 }
 
 void TypeMapTy::finishType(StructType *DTy, StructType *STy,
@@ -439,12 +447,6 @@ class IRLinker {
       FoundError = std::move(E);
   }
 
-  /// Most of the errors produced by this module are inconvertible StringErrors.
-  /// This convenience function lets us return one of those more easily.
-  Error stringErr(const Twine &T) {
-    return make_error<StringError>(T, inconvertibleErrorCode());
-  }
-
   /// Entry point for mapping values and alternate context for mapping aliases.
   ValueMapper Mapper;
   unsigned IndirectSymbolMCID;
@@ -875,7 +877,7 @@ void IRLinker::computeTypeMapping() {
 
   // Now that we have discovered all of the type equivalences, get a body for
   // any 'opaque' types in the dest module that are now resolved.
-  TypeMap.linkDefinedTypeBodies();
+  setError(TypeMap.linkDefinedTypeBodies());
 }
 
 static void getArrayElements(const Constant *C,

llvm/test/Assembler/mutually-recursive-types.ll

@@ -0,0 +1,7 @@
+; RUN: not llvm-as < %s 2>&1 | FileCheck %s
+
+; CHECK: error: identified structure type 'rt3' is recursive
+
+%rt1 = type { i32, { i8, %rt2, i8 }, i32 }
+%rt2 = type { i64, { i6, %rt3 } }
+%rt3 = type { %rt1 }

llvm/test/Assembler/unsized-recursive-type.ll

@@ -1,9 +1,5 @@
 ; RUN: not llvm-as < %s 2>&1 | FileCheck %s
 
-; CHECK: base element of getelementptr must be sized
+; CHECK: error: identified structure type 'myTy' is recursive
 
 %myTy = type { %myTy }
-define void @foo(ptr %p){
-  getelementptr %myTy, ptr %p, i64 1
-  ret void
-}

llvm/test/Linker/pr22807.ll

@@ -1,9 +1,6 @@
-; RUN: llvm-link -S -o - %p/pr22807.ll %p/Inputs/pr22807-1.ll %p/Inputs/pr22807-2.ll | FileCheck %s
+; RUN: not llvm-link -S -o - %p/pr22807.ll %p/Inputs/pr22807-1.ll %p/Inputs/pr22807-2.ll 2>&1 | FileCheck %s
 
-; CHECK-NOT: type
-; CHECK: %struct.B = type { %struct.A }
-; CHECK-NEXT: %struct.A = type { %struct.B }
-; CHECK-NOT: type
+; CHECK: error: identified structure type 'struct.A' is recursive
 
 %struct.B = type { %struct.A }
 %struct.A = type opaque