[CIR] Emit init of local variables (#130164)

Local variable initialization was previously being ignored. This change
adds support for initialization of scalar variables with constant values
and introduces the constant emitter framework.

Author: andykaylor

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

@@ -26,6 +26,10 @@ class CIRBaseBuilderTy : public mlir::OpBuilder {
   CIRBaseBuilderTy(mlir::MLIRContext &mlirContext)
       : mlir::OpBuilder(&mlirContext) {}
 
+  cir::ConstantOp getConstant(mlir::Location loc, mlir::TypedAttr attr) {
+    return create<cir::ConstantOp>(loc, attr.getType(), attr);
+  }
+
   cir::ConstantOp getBool(bool state, mlir::Location loc) {
     return create<cir::ConstantOp>(loc, getBoolTy(), getCIRBoolAttr(state));
   }

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

@@ -54,6 +54,20 @@ def CIR_BoolAttr : CIR_Attr<"Bool", "bool", [TypedAttrInterface]> {
   }];
 }
 
+//===----------------------------------------------------------------------===//
+// ZeroAttr
+//===----------------------------------------------------------------------===//
+
+def ZeroAttr : CIR_Attr<"Zero", "zero", [TypedAttrInterface]> {
+  let summary = "Attribute to represent zero initialization";
+  let description = [{
+    The ZeroAttr is used to indicate zero initialization on structs.
+  }];
+
+  let parameters = (ins AttributeSelfTypeParameter<"">:$type);
+  let assemblyFormat = [{}];
+}
+
 //===----------------------------------------------------------------------===//
 // UndefAttr
 //===----------------------------------------------------------------------===//

clang/include/clang/CIR/MissingFeatures.h

@@ -41,16 +41,17 @@ struct MissingFeatures {
   static bool supportComdat() { return false; }
 
   // Load/store attributes
-  static bool opLoadThreadLocal() { return false; }
+  static bool opLoadStoreThreadLocal() { return false; }
   static bool opLoadEmitScalarRangeCheck() { return false; }
   static bool opLoadBooleanRepresentation() { return false; }
   static bool opLoadStoreTbaa() { return false; }
   static bool opLoadStoreMemOrder() { return false; }
   static bool opLoadStoreVolatile() { return false; }
   static bool opLoadStoreAlignment() { return false; }
+  static bool opLoadStoreAtomic() { return false; }
+  static bool opLoadStoreObjC() { return false; }
 
   // AllocaOp handling
-  static bool opAllocaVarDeclContext() { return false; }
   static bool opAllocaStaticLocal() { return false; }
   static bool opAllocaNonGC() { return false; }
   static bool opAllocaImpreciseLifetime() { return false; }
@@ -61,6 +62,7 @@ struct MissingFeatures {
   static bool opAllocaReference() { return false; }
   static bool opAllocaAnnotations() { return false; }
   static bool opAllocaDynAllocSize() { return false; }
+  static bool opAllocaCaptureByInit() { return false; }
 
   // FuncOp handling
   static bool opFuncOpenCLKernelMetadata() { return false; }
@@ -76,6 +78,10 @@ struct MissingFeatures {
   static bool constructABIArgDirectExtend() { return false; }
   static bool opGlobalViewAttr() { return false; }
   static bool lowerModeOptLevel() { return false; }
+  static bool opTBAA() { return false; }
+  static bool objCLifetime() { return false; }
+  static bool emitNullabilityCheck() { return false; }
+  static bool astVarDeclInterface() { return false; }
 };
 
 } // namespace cir

clang/lib/CIR/CodeGen/CIRGenConstantEmitter.h

@@ -0,0 +1,100 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+//
+// A helper class for emitting expressions and values as cir::ConstantOp
+// and as initializers for global variables.
+//
+// Note: this is based on clang's LLVM IR codegen in ConstantEmitter.h, reusing
+// this class interface makes it easier move forward with bringing CIR codegen
+// to completion.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef CLANG_LIB_CIR_CODEGEN_CIRGENCONSTANTEMITTER_H
+#define CLANG_LIB_CIR_CODEGEN_CIRGENCONSTANTEMITTER_H
+
+#include "CIRGenFunction.h"
+#include "CIRGenModule.h"
+#include "llvm/ADT/SmallVector.h"
+
+namespace clang::CIRGen {
+
+class ConstantEmitter {
+public:
+  CIRGenModule &cgm;
+  const CIRGenFunction *cgf;
+
+private:
+  bool abstract = false;
+
+  /// Whether we're in a constant context.
+  bool inConstantContext = false;
+
+public:
+  /// Initialize this emission in the context of the given function.
+  /// Use this if the expression might contain contextual references like
+  /// block addresses or PredefinedExprs.
+  ConstantEmitter(CIRGenFunction &cgf) : cgm(cgf.cgm), cgf(&cgf) {}
+
+  ConstantEmitter(const ConstantEmitter &other) = delete;
+  ConstantEmitter &operator=(const ConstantEmitter &other) = delete;
+
+  // All of the "abstract" emission methods below permit the emission to
+  // be immediately discarded without finalizing anything.  Therefore, they
+  // must also promise not to do anything that will, in the future, require
+  // finalization:
+  //
+  //   - using the CGF (if present) for anything other than establishing
+  //     semantic context; for example, an expression with ignored
+  //     side-effects must not be emitted as an abstract expression
+  //
+  //   - doing anything that would not be safe to duplicate within an
+  //     initializer or to propagate to another context; for example,
+  //     side effects, or emitting an initialization that requires a
+  //     reference to its current location.
+  mlir::Attribute emitForMemory(mlir::Attribute c, QualType t);
+
+  /// Emit the result of the given expression as an abstract constant,
+  /// asserting that it succeeded.  This is only safe to do when the
+  /// expression is known to be a constant expression with either a fairly
+  /// simple type or a known simple form.
+  mlir::Attribute emitAbstract(SourceLocation loc, const APValue &value,
+                               QualType t);
+
+  mlir::Attribute tryEmitConstantExpr(const ConstantExpr *CE);
+
+  // These are private helper routines of the constant emitter that
+  // can't actually be private because things are split out into helper
+  // functions and classes.
+
+  mlir::Attribute tryEmitPrivateForVarInit(const VarDecl &d);
+
+  mlir::Attribute tryEmitPrivate(const APValue &value, QualType destType);
+  mlir::Attribute tryEmitPrivateForMemory(const APValue &value, QualType t);
+
+  /// Try to emit the initializer of the given declaration as an abstract
+  /// constant.
+  mlir::Attribute tryEmitAbstractForInitializer(const VarDecl &d);
+
+private:
+  class AbstractStateRAII {
+    ConstantEmitter &emitter;
+    bool oldValue;
+
+  public:
+    AbstractStateRAII(ConstantEmitter &emitter, bool value)
+        : emitter(emitter), oldValue(emitter.abstract) {
+      emitter.abstract = value;
+    }
+    ~AbstractStateRAII() { emitter.abstract = oldValue; }
+  };
+};
+
+} // namespace clang::CIRGen
+
+#endif // CLANG_LIB_CIR_CODEGEN_CIRGENCONSTANTEMITTER_H