[CIR] Upstream basic alloca and load support (#128792)

This change implements basic support in ClangIR for local variables
using the cir.alloca and cir.load operations.

Author: andykaylor

clang/include/clang/CIR/Dialect/Builder/CIRBaseBuilder.h

@@ -9,6 +9,7 @@
 #ifndef LLVM_CLANG_CIR_DIALECT_BUILDER_CIRBASEBUILDER_H
 #define LLVM_CLANG_CIR_DIALECT_BUILDER_CIRBASEBUILDER_H
 
+#include "clang/AST/CharUnits.h"
 #include "clang/CIR/Dialect/IR/CIRAttrs.h"
 #include "clang/CIR/Dialect/IR/CIRDialect.h"
 #include "clang/CIR/Dialect/IR/CIRTypes.h"
@@ -51,6 +52,47 @@ class CIRBaseBuilderTy : public mlir::OpBuilder {
     return cir::ConstPtrAttr::get(
         getContext(), mlir::cast<cir::PointerType>(type), valueAttr);
   }
+
+  mlir::Value createAlloca(mlir::Location loc, cir::PointerType addrType,
+                           mlir::Type type, llvm::StringRef name,
+                           mlir::IntegerAttr alignment) {
+    return create<cir::AllocaOp>(loc, addrType, type, name, alignment);
+  }
+
+  cir::LoadOp createLoad(mlir::Location loc, mlir::Value ptr,
+                         bool isVolatile = false, uint64_t alignment = 0) {
+    mlir::IntegerAttr intAttr;
+    if (alignment)
+      intAttr = mlir::IntegerAttr::get(
+          mlir::IntegerType::get(ptr.getContext(), 64), alignment);
+
+    return create<cir::LoadOp>(loc, ptr);
+  }
+
+  //
+  // Block handling helpers
+  // ----------------------
+  //
+  static OpBuilder::InsertPoint getBestAllocaInsertPoint(mlir::Block *block) {
+    auto last =
+        std::find_if(block->rbegin(), block->rend(), [](mlir::Operation &op) {
+          // TODO: Add LabelOp missing feature here
+          return mlir::isa<cir::AllocaOp>(&op);
+        });
+
+    if (last != block->rend())
+      return OpBuilder::InsertPoint(block, ++mlir::Block::iterator(&*last));
+    return OpBuilder::InsertPoint(block, block->begin());
+  };
+
+  mlir::IntegerAttr getSizeFromCharUnits(mlir::MLIRContext *ctx,
+                                         clang::CharUnits size) {
+    // Note that mlir::IntegerType is used instead of cir::IntType here
+    // because we don't need sign information for this to be useful, so keep
+    // it simple.
+    return mlir::IntegerAttr::get(mlir::IntegerType::get(ctx, 64),
+                                  size.getQuantity());
+  }
 };
 
 } // namespace cir

clang/include/clang/CIR/Dialect/IR/CIRAttrs.td

@@ -54,6 +54,21 @@ def CIR_BoolAttr : CIR_Attr<"Bool", "bool", [TypedAttrInterface]> {
   }];
 }
 
+//===----------------------------------------------------------------------===//
+// UndefAttr
+//===----------------------------------------------------------------------===//
+
+def UndefAttr : CIR_Attr<"Undef", "undef", [TypedAttrInterface]> {
+  let summary = "Represent an undef constant";
+  let description = [{
+    The UndefAttr represents an undef constant, corresponding to LLVM's notion
+    of undef.
+  }];
+
+  let parameters = (ins AttributeSelfTypeParameter<"">:$type);
+  let assemblyFormat = [{}];
+}
+
 //===----------------------------------------------------------------------===//
 // IntegerAttr
 //===----------------------------------------------------------------------===//

clang/include/clang/CIR/Dialect/IR/CIROps.td

@@ -115,6 +115,119 @@ def ConstantOp : CIR_Op<"const",
   let hasFolder = 1;
 }
 
+//===----------------------------------------------------------------------===//
+// AllocaOp
+//===----------------------------------------------------------------------===//
+
+class AllocaTypesMatchWith<string summary, string lhsArg, string rhsArg,
+                     string transform, string comparator = "std::equal_to<>()">
+  : PredOpTrait<summary, CPred<
+      comparator # "(" #
+      !subst("$_self", "$" # lhsArg # ".getType()", transform) #
+             ", $" # rhsArg # ")">> {
+  string lhs = lhsArg;
+  string rhs = rhsArg;
+  string transformer = transform;
+}
+
+def AllocaOp : CIR_Op<"alloca", [
+  AllocaTypesMatchWith<"'allocaType' matches pointee type of 'addr'",
+                 "addr", "allocaType",
+                 "cast<PointerType>($_self).getPointee()">,
+                 DeclareOpInterfaceMethods<PromotableAllocationOpInterface>]> {
+  let summary = "Defines a scope-local variable";
+  let description = [{
+    The `cir.alloca` operation defines a scope-local variable.
+
+    The presence of the `const` attribute indicates that the local variable is
+    declared with C/C++ `const` keyword.
+
+    The result type is a pointer to the input's type.
+
+    Example:
+
+    ```mlir
+    // int count;
+    %0 = cir.alloca i32, !cir.ptr<i32>, ["count"] {alignment = 4 : i64}
+
+    // int *ptr;
+    %1 = cir.alloca !cir.ptr<i32>, !cir.ptr<!cir.ptr<i32>>, ["ptr"] {alignment = 8 : i64}
+    ...
+    ```
+  }];
+
+  let arguments = (ins
+    TypeAttr:$allocaType,
+    StrAttr:$name,
+    UnitAttr:$init,
+    UnitAttr:$constant,
+    ConfinedAttr<OptionalAttr<I64Attr>, [IntMinValue<0>]>:$alignment,
+    OptionalAttr<ArrayAttr>:$annotations
+  );
+
+  let results = (outs Res<CIR_PointerType, "",
+                      [MemAlloc<AutomaticAllocationScopeResource>]>:$addr);
+
+  let skipDefaultBuilders = 1;
+  let builders = [
+    OpBuilder<(ins "mlir::Type":$addr,
+                   "mlir::Type":$allocaType,
+                   "llvm::StringRef":$name,
+                   "mlir::IntegerAttr":$alignment)>
+  ];
+
+  let extraClassDeclaration = [{
+    // Whether the alloca input type is a pointer.
+    bool isPointerType() { return ::mlir::isa<::cir::PointerType>(getAllocaType()); }
+  }];
+
+  let assemblyFormat = [{
+    $allocaType `,` qualified(type($addr)) `,`
+    `[` $name
+       (`,` `init` $init^)?
+       (`,` `const` $constant^)?
+    `]`
+    ($annotations^)? attr-dict
+  }];
+
+  let hasVerifier = 0;
+}
+
+//===----------------------------------------------------------------------===//
+// LoadOp
+//===----------------------------------------------------------------------===//
+
+def LoadOp : CIR_Op<"load", [
+  TypesMatchWith<"type of 'result' matches pointee type of 'addr'",
+                 "addr", "result",
+                 "cast<PointerType>($_self).getPointee()">,
+                 DeclareOpInterfaceMethods<PromotableMemOpInterface>]> {
+
+  let summary = "Load value from memory adddress";
+  let description = [{
+    `cir.load` reads a value (lvalue to rvalue conversion) given an address
+    backed up by a `cir.ptr` type.
+
+    Example:
+
+    ```mlir
+
+    // Read from local variable, address in %0.
+    %1 = cir.load %0 : !cir.ptr<i32>, i32
+    ```
+  }];
+
+  let arguments = (ins Arg<CIR_PointerType, "the address to load from",
+                           [MemRead]>:$addr);
+  let results = (outs CIR_AnyType:$result);
+
+  let assemblyFormat = [{
+    $addr `:` qualified(type($addr)) `,` type($result) attr-dict
+  }];
+
+  // FIXME: add verifier.
+}
+
 //===----------------------------------------------------------------------===//
 // ReturnOp
 //===----------------------------------------------------------------------===//

clang/include/clang/CIR/MissingFeatures.h

@@ -30,12 +30,35 @@ struct MissingFeatures {
   // This isn't needed until we add support for bools.
   static bool convertTypeForMemory() { return false; }
 
+  // CIRGenFunction implementation details
+  static bool cgfSymbolTable() { return false; }
+
   // Unhandled global/linkage information.
   static bool opGlobalDSOLocal() { return false; }
   static bool opGlobalThreadLocal() { return false; }
   static bool opGlobalConstant() { return false; }
   static bool opGlobalAlignment() { return false; }
   static bool opGlobalLinkage() { return false; }
+
+  // Load attributes
+  static bool opLoadThreadLocal() { return false; }
+  static bool opLoadEmitScalarRangeCheck() { return false; }
+  static bool opLoadBooleanRepresentation() { return false; }
+
+  // AllocaOp handling
+  static bool opAllocaVarDeclContext() { return false; }
+  static bool opAllocaStaticLocal() { return false; }
+  static bool opAllocaNonGC() { return false; }
+  static bool opAllocaImpreciseLifetime() { return false; }
+  static bool opAllocaPreciseLifetime() { return false; }
+  static bool opAllocaTLS() { return false; }
+  static bool opAllocaOpenMPThreadPrivate() { return false; }
+  static bool opAllocaEscapeByReference() { return false; }
+  static bool opAllocaReference() { return false; }
+
+  // Misc
+  static bool scalarConversionOpts() { return false; }
+  static bool tryEmitAsConstant() { return false; }
 };
 
 } // namespace cir

clang/lib/CIR/CodeGen/Address.h

@@ -0,0 +1,76 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This class provides a simple wrapper for a pair of a pointer and an
+// alignment.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef CLANG_LIB_CIR_ADDRESS_H
+#define CLANG_LIB_CIR_ADDRESS_H
+
+#include "mlir/IR/Value.h"
+#include "clang/AST/CharUnits.h"
+#include "clang/CIR/Dialect/IR/CIRTypes.h"
+#include "llvm/ADT/PointerIntPair.h"
+
+namespace clang::CIRGen {
+
+class Address {
+
+  // The boolean flag indicates whether the pointer is known to be non-null.
+  llvm::PointerIntPair<mlir::Value, 1, bool> pointerAndKnownNonNull;
+
+  /// The expected CIR type of the pointer. Carrying accurate element type
+  /// information in Address makes it more convenient to work with Address
+  /// values and allows frontend assertions to catch simple mistakes.
+  mlir::Type elementType;
+
+  clang::CharUnits alignment;
+
+protected:
+  Address(std::nullptr_t) : elementType(nullptr) {}
+
+public:
+  Address(mlir::Value pointer, mlir::Type elementType,
+          clang::CharUnits alignment)
+      : pointerAndKnownNonNull(pointer, false), elementType(elementType),
+        alignment(alignment) {
+    assert(mlir::isa<cir::PointerType>(pointer.getType()) &&
+           "Expected cir.ptr type");
+
+    assert(pointer && "Pointer cannot be null");
+    assert(elementType && "Element type cannot be null");
+    assert(!alignment.isZero() && "Alignment cannot be zero");
+
+    assert(mlir::cast<cir::PointerType>(pointer.getType()).getPointee() ==
+           elementType);
+  }
+
+  static Address invalid() { return Address(nullptr); }
+  bool isValid() const {
+    return pointerAndKnownNonNull.getPointer() != nullptr;
+  }
+
+  mlir::Value getPointer() const {
+    assert(isValid());
+    return pointerAndKnownNonNull.getPointer();
+  }
+
+  mlir::Type getElementType() const {
+    assert(isValid());
+    assert(mlir::cast<cir::PointerType>(
+               pointerAndKnownNonNull.getPointer().getType())
+               .getPointee() == elementType);
+    return elementType;
+  }
+};
+
+} // namespace clang::CIRGen
+
+#endif // CLANG_LIB_CIR_ADDRESS_H