[SVE] Make VectorType::getNumElements() complain for scalable vectors

[ctetreau]

Summary

Piggy-back off of TypeSize's STRICT_FIXED_SIZE_VECTORS flag and:

• if it is defined, assert that the vector is not scalable
• if it is not defined, complain if the vector is scalable

[sdesmalen]

LGTM

[ctetreau]

fix broken tests

[nikic]

llvm/include/llvm/IR/DerivedTypes.h

421

Tiny style nit: This line seems unnecessary, as EC is already a member of VectorType.

llvm/CMakeLists.txt

if( NOT uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG" )
   option(LLVM_ENABLE_ASSERTIONS "Enable assertions" OFF)
 else()
   option(LLVM_ENABLE_ASSERTIONS "Enable assertions" ON)
 endif()
 
 option(LLVM_ENABLE_EXPENSIVE_CHECKS "Enable expensive checks" OFF)
 
 # While adding scalable vector support to LLVM, we temporarily want to
-# allow an implicit conversion of TypeSize to uint64_t. This CMake flag
-# enables a more strict conversion where it asserts that the type is not
-# a scalable vector type.
+# allow an implicit conversion of TypeSize to uint64_t, and to allow
+# code to get the fixed number of elements from a possibly scalable vector.
+# This CMake flag enables a more strict mode where it asserts that the type
+# is not a scalable vector type.
 #
 # Enabling this flag makes it easier to find cases where the compiler makes
 # assumptions on the size being 'fixed size', when building tests for
 # SVE/SVE2 or other scalable vector architectures.
 option(LLVM_ENABLE_STRICT_FIXED_SIZE_VECTORS
-       "Enable assertions that type is not scalable in implicit conversion from TypeSize to uint64_t" OFF)
+       "Enable assertions that type is not scalable in implicit conversion from TypeSize to uint64_t and calls to getNumElements" OFF)
 
 set(LLVM_ABI_BREAKING_CHECKS "WITH_ASSERTS" CACHE STRING
   "Enable abi-breaking checks.  Can be WITH_ASSERTS, FORCE_ON or FORCE_OFF.")
 
 option(LLVM_FORCE_USE_OLD_TOOLCHAIN
        "Set to ON to force using an old, unsupported host toolchain." OFF)
 
 option(LLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN

llvm/include/llvm/IR/DerivedTypes.h

 
 public:
   VectorType(const VectorType &) = delete;
   VectorType &operator=(const VectorType &) = delete;
 
   /// Get the number of elements in this vector. It does not make sense to call
   /// this function on a scalable vector, and this will be moved into
   /// FixedVectorType in a future commit
-  unsigned getNumElements() const { return EC.Min; }
+  unsigned getNumElements() const {
+    ElementCount EC = getElementCount();
+#ifdef STRICT_FIXED_SIZE_VECTORS
+    assert(!EC.Scalable &&
+           "Request for fixed number of elements from scalable vector");
+    return EC.Min;
+#else
+    if (EC.Scalable)
+      WithColor::warning()
+          << "The code that requested the fixed number of elements has made "
+             "the assumption that this vector is not scalable. This assumption "
+             "was not correct, and this may lead to broken code\n";
+    return EC.Min;
+#endif
+  }
 
   Type *getElementType() const { return ContainedType; }
 
   /// This static method is the primary way to construct an VectorType.
   static VectorType *get(Type *ElementType, ElementCount EC);
   static VectorType *get(Type *ElementType, unsigned NumElements,
                          bool Scalable = false) {
     return VectorType::get(ElementType, {NumElements, Scalable});

llvm/lib/IR/AsmWriter.cpp

case Type::ArrayTyID: {
     OS << '[' << ATy->getNumElements() << " x ";
     print(ATy->getElementType(), OS);
     OS << ']';
     return;
   }
   case Type::FixedVectorTyID:
   case Type::ScalableVectorTyID: {
     VectorType *PTy = cast<VectorType>(Ty);
+    ElementCount EC = PTy->getElementCount();
     OS << "<";
-    if (PTy->isScalable())
+    if (EC.Scalable)
       OS << "vscale x ";
-    OS << PTy->getNumElements() << " x ";
+    OS << EC.Min << " x ";
     print(PTy->getElementType(), OS);
     OS << '>';
     return;
   }
   }
   llvm_unreachable("Invalid TypeID");
 }
 

llvm/lib/IR/Function.cpp

if (PointerType* PTyp = dyn_cast<PointerType>(Ty)) {
     Result += "f_" + getMangledTypeStr(FT->getReturnType());
     for (size_t i = 0; i < FT->getNumParams(); i++)
       Result += getMangledTypeStr(FT->getParamType(i));
     if (FT->isVarArg())
       Result += "vararg";
     // Ensure nested function types are distinguishable.
     Result += "f";
   } else if (VectorType* VTy = dyn_cast<VectorType>(Ty)) {
-    if (VTy->isScalable())
+    ElementCount EC = VTy->getElementCount();
+    if (EC.Scalable)
       Result += "nx";
-    Result += "v" + utostr(VTy->getNumElements()) +
-              getMangledTypeStr(VTy->getElementType());
+    Result += "v" + utostr(EC.Min) + getMangledTypeStr(VTy->getElementType());
   } else if (Ty) {
     switch (Ty->getTypeID()) {
     default: llvm_unreachable("Unhandled type");
     case Type::VoidTyID:      Result += "isVoid";   break;
     case Type::MetadataTyID:  Result += "Metadata"; break;
     case Type::HalfTyID:      Result += "f16";      break;
     case Type::FloatTyID:     Result += "f32";      break;
     case Type::DoubleTyID:    Result += "f64";      break;