[CIR] Upstream support for variable length arrays

clang/lib/CIR/CodeGen/CIRGenBuilder.h

@@ -519,6 +519,14 @@ class CIRGenBuilderTy : public cir::CIRBaseBuilderTy {
     return createGlobal(module, loc, uniqueName, type, isConstant, linkage);
   }
 
+  cir::StackSaveOp createStackSave(mlir::Location loc, mlir::Type ty) {
+    return cir::StackSaveOp::create(*this, loc, ty);
+  }
+
+  cir::StackRestoreOp createStackRestore(mlir::Location loc, mlir::Value v) {
+    return cir::StackRestoreOp::create(*this, loc, v);
+  }
+
   mlir::Value createSetBitfield(mlir::Location loc, mlir::Type resultType,
                                 Address dstAddr, mlir::Type storageType,
                                 mlir::Value src, const CIRGenBitFieldInfo &info,

clang/lib/CIR/CodeGen/CIRGenDecl.cpp

@@ -44,38 +44,70 @@ CIRGenFunction::emitAutoVarAlloca(const VarDecl &d,
 
   // If the type is variably-modified, emit all the VLA sizes for it.
   if (ty->isVariablyModifiedType())
-    cgm.errorNYI(d.getSourceRange(), "emitAutoVarDecl: variably modified type");
+    emitVariablyModifiedType(ty);
 
   assert(!cir::MissingFeatures::openMP());
 
   Address address = Address::invalid();
-  if (!ty->isConstantSizeType())
-    cgm.errorNYI(d.getSourceRange(), "emitAutoVarDecl: non-constant size type");
-
-  // A normal fixed sized variable becomes an alloca in the entry block,
-  // unless:
-  // - it's an NRVO variable.
-  // - we are compiling OpenMP and it's an OpenMP local variable.
-  if (nrvo) {
-    // The named return value optimization: allocate this variable in the
-    // return slot, so that we can elide the copy when returning this
-    // variable (C++0x [class.copy]p34).
-    address = returnValue;
-
-    if (const RecordDecl *rd = ty->getAsRecordDecl()) {
-      if (const auto *cxxrd = dyn_cast<CXXRecordDecl>(rd);
-          (cxxrd && !cxxrd->hasTrivialDestructor()) ||
-          rd->isNonTrivialToPrimitiveDestroy())
-        cgm.errorNYI(d.getSourceRange(), "emitAutoVarAlloca: set NRVO flag");
+  if (ty->isConstantSizeType()) {
+    // A normal fixed sized variable becomes an alloca in the entry block,
+    // unless:
+    // - it's an NRVO variable.
+    // - we are compiling OpenMP and it's an OpenMP local variable.
+    if (nrvo) {
+      // The named return value optimization: allocate this variable in the
+      // return slot, so that we can elide the copy when returning this
+      // variable (C++0x [class.copy]p34).
+      address = returnValue;
+
+      if (const RecordDecl *rd = ty->getAsRecordDecl()) {
+        if (const auto *cxxrd = dyn_cast<CXXRecordDecl>(rd);
+            (cxxrd && !cxxrd->hasTrivialDestructor()) ||
+            rd->isNonTrivialToPrimitiveDestroy())
+          cgm.errorNYI(d.getSourceRange(), "emitAutoVarAlloca: set NRVO flag");
+      }
+    } else {
+      // A normal fixed sized variable becomes an alloca in the entry block,
+      mlir::Type allocaTy = convertTypeForMem(ty);
+      // Create the temp alloca and declare variable using it.
+      address = createTempAlloca(allocaTy, alignment, loc, d.getName(),
+                                 /*arraySize=*/nullptr, /*alloca=*/nullptr, ip);
+      declare(address.getPointer(), &d, ty, getLoc(d.getSourceRange()),
+              alignment);
     }
   } else {
-    // A normal fixed sized variable becomes an alloca in the entry block,
-    mlir::Type allocaTy = convertTypeForMem(ty);
-    // Create the temp alloca and declare variable using it.
-    address = createTempAlloca(allocaTy, alignment, loc, d.getName(),
-                               /*arraySize=*/nullptr, /*alloca=*/nullptr, ip);
-    declare(address.getPointer(), &d, ty, getLoc(d.getSourceRange()),
-            alignment);
+    // Non-constant size type
+    assert(!cir::MissingFeatures::openMP());
+    if (!didCallStackSave) {
+      // Save the stack.
+      cir::PointerType defaultTy = AllocaInt8PtrTy;
+      CharUnits align = CharUnits::fromQuantity(
+          cgm.getDataLayout().getAlignment(defaultTy, false));
+      Address stack = createTempAlloca(defaultTy, align, loc, "saved_stack");
+
+      mlir::Value v = builder.createStackSave(loc, defaultTy);
+      assert(v.getType() == AllocaInt8PtrTy);
+      builder.createStore(loc, v, stack);
+
+      didCallStackSave = true;
+
+      // Push a cleanup block and restore the stack there.
+      // FIXME: in general circumstances, this should be an EH cleanup.
+      pushStackRestore(NormalCleanup, stack);
+    }
+
+    VlaSizePair vlaSize = getVLASize(ty);
+    mlir::Type memTy = convertTypeForMem(vlaSize.type);
+
+    // Allocate memory for the array.
+    address =
+        createTempAlloca(memTy, alignment, loc, d.getName(), vlaSize.numElts,
+                         /*alloca=*/nullptr, builder.saveInsertionPoint());
+
+    // If we have debug info enabled, properly describe the VLA dimensions for
+    // this type by registering the vla size expression for each of the
+    // dimensions.
+    assert(!cir::MissingFeatures::generateDebugInfo());
   }
 
   emission.addr = address;
@@ -696,6 +728,16 @@ struct DestroyObject final : EHScopeStack::Cleanup {
     cgf.emitDestroy(addr, type, destroyer);
   }
 };
+
+struct CallStackRestore final : EHScopeStack::Cleanup {
+  Address stack;
+  CallStackRestore(Address stack) : stack(stack) {}
+  void emit(CIRGenFunction &cgf) override {
+    mlir::Location loc = stack.getPointer().getLoc();
+    mlir::Value v = cgf.getBuilder().createLoad(loc, stack);
+    cgf.getBuilder().createStackRestore(loc, v);
+  }
+};
 } // namespace
 
 void CIRGenFunction::pushDestroy(CleanupKind cleanupKind, Address addr,
@@ -805,6 +847,10 @@ CIRGenFunction::getDestroyer(QualType::DestructionKind kind) {
   llvm_unreachable("Unknown DestructionKind");
 }
 
+void CIRGenFunction::pushStackRestore(CleanupKind kind, Address spMem) {
+  ehStack.pushCleanup<CallStackRestore>(kind, spMem);
+}
+
 /// Enter a destroy cleanup for the given local variable.
 void CIRGenFunction::emitAutoVarTypeCleanup(
     const CIRGenFunction::AutoVarEmission &emission,

clang/lib/CIR/CodeGen/CIRGenExpr.cpp

@@ -2068,7 +2068,7 @@ mlir::Value CIRGenFunction::emitAlloca(StringRef name, mlir::Type ty,
     mlir::OpBuilder::InsertionGuard guard(builder);
     builder.restoreInsertionPoint(ip);
     addr = builder.createAlloca(loc, /*addr type*/ localVarPtrTy,
-                                /*var type*/ ty, name, alignIntAttr);
+                                /*var type*/ ty, name, alignIntAttr, arraySize);
     assert(!cir::MissingFeatures::astVarDeclInterface());
   }
   return addr;

clang/lib/CIR/CodeGen/CIRGenFunction.cpp

@@ -410,6 +410,8 @@ void CIRGenFunction::startFunction(GlobalDecl gd, QualType returnType,
   curFn = fn;
 
   const Decl *d = gd.getDecl();
+
+  didCallStackSave = false;
   curCodeDecl = d;
   const auto *fd = dyn_cast_or_null<FunctionDecl>(d);
   curFuncDecl = d->getNonClosureContext();
@@ -1006,6 +1008,41 @@ mlir::Value CIRGenFunction::emitAlignmentAssumption(
                                  offsetValue);
 }
 
+CIRGenFunction::VlaSizePair CIRGenFunction::getVLASize(QualType type) {
+  const VariableArrayType *vla =
+      cgm.getASTContext().getAsVariableArrayType(type);
+  assert(vla && "type was not a variable array type!");
+  return getVLASize(vla);
+}
+
+CIRGenFunction::VlaSizePair
+CIRGenFunction::getVLASize(const VariableArrayType *type) {
+  // The number of elements so far; always size_t.
+  mlir::Value numElements;
+
+  QualType elementType;
+  do {
+    elementType = type->getElementType();
+    mlir::Value vlaSize = vlaSizeMap[type->getSizeExpr()];
+    assert(vlaSize && "no size for VLA!");
+    assert(vlaSize.getType() == SizeTy);
+
+    if (!numElements) {
+      numElements = vlaSize;
+    } else {
+      // It's undefined behavior if this wraps around, so mark it that way.
+      // FIXME: Teach -fsanitize=undefined to trap this.
+
+      numElements =
+          builder.createMul(numElements.getLoc(), numElements, vlaSize,
+                            cir::OverflowBehavior::NoUnsignedWrap);
+    }
+  } while ((type = getContext().getAsVariableArrayType(elementType)));
+
+  assert(numElements && "Undefined elements number");
+  return {numElements, elementType};
+}
+
 // TODO(cir): Most of this function can be shared between CIRGen
 // and traditional LLVM codegen
 void CIRGenFunction::emitVariablyModifiedType(QualType type) {
@@ -1086,7 +1123,26 @@ void CIRGenFunction::emitVariablyModifiedType(QualType type) {
       break;
 
     case Type::VariableArray: {
-      cgm.errorNYI("CIRGenFunction::emitVariablyModifiedType VLA");
+      // Losing element qualification here is fine.
+      const VariableArrayType *vat = cast<clang::VariableArrayType>(ty);
+
+      // Unknown size indication requires no size computation.
+      // Otherwise, evaluate and record it.
+      if (const Expr *sizeExpr = vat->getSizeExpr()) {
+        // It's possible that we might have emitted this already,
+        // e.g. with a typedef and a pointer to it.
+        mlir::Value &entry = vlaSizeMap[sizeExpr];
+        if (!entry) {
+          mlir::Value size = emitScalarExpr(sizeExpr);
+          assert(!cir::MissingFeatures::sanitizers());
+
+          // Always zexting here would be wrong if it weren't
+          // undefined behavior to have a negative bound.
+          // FIXME: What about when size's type is larger than size_t?
+          entry = builder.createIntCast(size, SizeTy);
+        }
+      }
+      type = vat->getElementType();
       break;
     }
 

clang/lib/CIR/CodeGen/CIRGenFunction.h

@@ -149,6 +149,10 @@ class CIRGenFunction : public CIRGenTypeCache {
   using SymTableTy = llvm::ScopedHashTable<const clang::Decl *, mlir::Value>;
   SymTableTy symbolTable;
 
+  /// Whether a cir.stacksave operation has been added. Used to avoid
+  /// inserting cir.stacksave for multiple VLAs in the same scope.
+  bool didCallStackSave = false;
+
   /// Whether or not a Microsoft-style asm block has been processed within
   /// this fuction. These can potentially set the return value.
   bool sawAsmBlock = false;
@@ -188,6 +192,14 @@ class CIRGenFunction : public CIRGenTypeCache {
   llvm::DenseMap<const OpaqueValueExpr *, LValue> opaqueLValues;
   llvm::DenseMap<const OpaqueValueExpr *, RValue> opaqueRValues;
 
+  // This keeps track of the associated size for each VLA type.
+  // We track this by the size expression rather than the type itself because
+  // in certain situations, like a const qualifier applied to an VLA typedef,
+  // multiple VLA types can share the same size expression.
+  // FIXME: Maybe this could be a stack of maps that is pushed/popped as we
+  // enter/leave scopes.
+  llvm::DenseMap<const Expr *, mlir::Value> vlaSizeMap;
+
 public:
   /// A non-RAII class containing all the information about a bound
   /// opaque value.  OpaqueValueMapping, below, is a RAII wrapper for
@@ -436,6 +448,20 @@ class CIRGenFunction : public CIRGenTypeCache {
     }
   };
 
+  struct VlaSizePair {
+    mlir::Value numElts;
+    QualType type;
+
+    VlaSizePair(mlir::Value num, QualType ty) : numElts(num), type(ty) {}
+  };
+
+  /// Returns an MLIR::Value+QualType pair that corresponds to the size,
+  /// in non-variably-sized elements, of a variable length array type,
+  /// plus that largest non-variably-sized element type.  Assumes that
+  /// the type has already been emitted with emitVariablyModifiedType.
+  VlaSizePair getVLASize(const VariableArrayType *type);
+  VlaSizePair getVLASize(QualType type);
+
   void finishFunction(SourceLocation endLoc);
 
   /// Determine whether the given initializer is trivial in the sense
@@ -583,6 +609,8 @@ class CIRGenFunction : public CIRGenTypeCache {
     return needsEHCleanup(kind) ? NormalAndEHCleanup : NormalCleanup;
   }
 
+  void pushStackRestore(CleanupKind kind, Address spMem);
+
   /// Set the address of a local variable.
   void setAddrOfLocalVar(const clang::VarDecl *vd, Address addr) {
     assert(!localDeclMap.count(vd) && "Decl already exists in LocalDeclMap!");
@@ -854,6 +882,7 @@ class CIRGenFunction : public CIRGenTypeCache {
 
   protected:
     bool performCleanup;
+    bool oldDidCallStackSave;
 
   private:
     RunCleanupsScope(const RunCleanupsScope &) = delete;
@@ -867,6 +896,8 @@ class CIRGenFunction : public CIRGenTypeCache {
     explicit RunCleanupsScope(CIRGenFunction &cgf)
         : performCleanup(true), cgf(cgf) {
       cleanupStackDepth = cgf.ehStack.stable_begin();
+      oldDidCallStackSave = cgf.didCallStackSave;
+      cgf.didCallStackSave = false;
       oldCleanupStackDepth = cgf.currentCleanupStackDepth;
       cgf.currentCleanupStackDepth = cleanupStackDepth;
     }
@@ -883,6 +914,7 @@ class CIRGenFunction : public CIRGenTypeCache {
       assert(performCleanup && "Already forced cleanup");
       {
         mlir::OpBuilder::InsertionGuard guard(cgf.getBuilder());
+        cgf.didCallStackSave = oldDidCallStackSave;
         cgf.popCleanupBlocks(cleanupStackDepth);
         performCleanup = false;
         cgf.currentCleanupStackDepth = oldCleanupStackDepth;

clang/lib/CIR/CodeGen/CIRGenModule.cpp

@@ -88,6 +88,8 @@ CIRGenModule::CIRGenModule(mlir::MLIRContext &mlirContext,
   FP80Ty = cir::FP80Type::get(&getMLIRContext());
   FP128Ty = cir::FP128Type::get(&getMLIRContext());
 
+  AllocaInt8PtrTy = cir::PointerType::get(UInt8Ty, cirAllocaAddressSpace);
+
   PointerAlignInBytes =
       astContext
           .toCharUnitsFromBits(

clang/lib/CIR/CodeGen/CIRGenTypeCache.h

@@ -65,6 +65,9 @@ struct CIRGenTypeCache {
   cir::PointerType VoidPtrTy;
   cir::PointerType UInt8PtrTy;
 
+  /// void* in alloca address space
+  cir::PointerType AllocaInt8PtrTy;
+
   /// The size and alignment of a pointer into the generic address space.
   union {
     unsigned char PointerAlignInBytes;

clang/lib/CIR/CodeGen/CIRGenTypes.cpp

@@ -421,6 +421,16 @@ mlir::Type CIRGenTypes::convertType(QualType type) {
     break;
   }
 
+  case Type::VariableArray: {
+    const VariableArrayType *a = cast<VariableArrayType>(ty);
+    if (a->getIndexTypeCVRQualifiers() != 0)
+      cgm.errorNYI(SourceLocation(), "non trivial array types", type);
+    // VLAs resolve to the innermost element type; this matches
+    // the return of alloca, and there isn't any obviously better choice.
+    resultType = convertTypeForMem(a->getElementType());
+    break;
+  }
+
   case Type::IncompleteArray: {
     const IncompleteArrayType *arrTy = cast<IncompleteArrayType>(ty);
     if (arrTy->getIndexTypeCVRQualifiers() != 0)