[clang] [CIR][NFC] Refactor constant pointer l-value handling (PR #144165)

[Andy Kaylor via cfe-commits]

================
@@ -329,6 +329,222 @@ emitArrayConstant(CIRGenModule &cgm, mlir::Type desiredType,
   return {};
 }
 
+//===----------------------------------------------------------------------===//
+//                          ConstantLValueEmitter
+//===----------------------------------------------------------------------===//
+
+namespace {
+/// A struct which can be used to peephole certain kinds of finalization
+/// that normally happen during l-value emission.
+struct ConstantLValue {
+  llvm::PointerUnion<mlir::Value, mlir::Attribute> value;
+  bool hasOffsetApplied;
+
+  ConstantLValue(std::nullptr_t) : value(nullptr), hasOffsetApplied(false) {}
+  ConstantLValue() : value(nullptr), hasOffsetApplied(false) {}
+};
+
+/// A helper class for emitting constant l-values.
+class ConstantLValueEmitter
+    : public ConstStmtVisitor<ConstantLValueEmitter, ConstantLValue> {
+  CIRGenModule &cgm;
+  ConstantEmitter &emitter;
+  const APValue &value;
+  QualType destType;
+
+  // Befriend StmtVisitorBase so that we don't have to expose Visit*.
+  friend StmtVisitorBase;
+
+public:
+  ConstantLValueEmitter(ConstantEmitter &emitter, const APValue &value,
+                        QualType destType)
+      : cgm(emitter.cgm), emitter(emitter), value(value), destType(destType) {}
+
+  mlir::Attribute tryEmit();
+
+private:
+  mlir::Attribute tryEmitAbsolute(mlir::Type destTy);
+  ConstantLValue tryEmitBase(const APValue::LValueBase &base);
+
+  ConstantLValue VisitStmt(const Stmt *s) { return nullptr; }
+  ConstantLValue VisitConstantExpr(const ConstantExpr *e);
+  ConstantLValue VisitCompoundLiteralExpr(const CompoundLiteralExpr *e);
+  ConstantLValue VisitStringLiteral(const StringLiteral *e);
+  ConstantLValue VisitObjCBoxedExpr(const ObjCBoxedExpr *e);
+  ConstantLValue VisitObjCEncodeExpr(const ObjCEncodeExpr *e);
+  ConstantLValue VisitObjCStringLiteral(const ObjCStringLiteral *e);
+  ConstantLValue VisitPredefinedExpr(const PredefinedExpr *e);
+  ConstantLValue VisitAddrLabelExpr(const AddrLabelExpr *e);
+  ConstantLValue VisitCallExpr(const CallExpr *e);
+  ConstantLValue VisitBlockExpr(const BlockExpr *e);
+  ConstantLValue VisitCXXTypeidExpr(const CXXTypeidExpr *e);
+  ConstantLValue
+  VisitMaterializeTemporaryExpr(const MaterializeTemporaryExpr *e);
+};
+
+} // namespace
+
+mlir::Attribute ConstantLValueEmitter::tryEmit() {
+  const APValue::LValueBase &base = value.getLValueBase();
+
+  // The destination type should be a pointer or reference
+  // type, but it might also be a cast thereof.
+  //
+  // FIXME: the chain of casts required should be reflected in the APValue.
+  // We need this in order to correctly handle things like a ptrtoint of a
+  // non-zero null pointer and addrspace casts that aren't trivially
+  // represented in LLVM IR.
+  mlir::Type destTy = cgm.getTypes().convertTypeForMem(destType);
+  assert(mlir::isa<cir::PointerType>(destTy));
+
+  // If there's no base at all, this is a null or absolute pointer,
+  // possibly cast back to an integer type.
+  if (!base)
+    return tryEmitAbsolute(destTy);
----------------
andykaylor wrote:

This is the only path that doesn't hit an `errorNYI` call, and along with the `convertTypeForMem` call above, it should correspond exactly to the previous implementation.

https://github.com/llvm/llvm-project/pull/144165