[lld] [LLD] Improve linker script handing in LLD (PR #106334)

[via llvm-commits]

================
@@ -74,6 +75,106 @@ struct ExprValue {
 // Later, we evaluate the expression by calling the function.
 using Expr = std::function<ExprValue()>;
 
+class ScriptExpr {
+public:
+  enum class ExprKind : uint8_t { Constant, Dynamic, Unary, Binary };
+
+private:
+  ExprKind kind_;
+
+protected:
+  explicit ScriptExpr(ExprKind kind) : kind_(kind) {}
+
+public:
+  ExprKind getKind() const { return kind_; }
+  std::function<ExprValue()> getExpr() const;
+  ExprValue getExprValue() const;
+};
+
+class ConstantExpr : public ScriptExpr {
+public:
+  ConstantExpr(uint64_t val) : ScriptExpr(ExprKind::Constant), val_(val) {}
+  ExprValue getExprValue() const { return ExprValue(val_); }
+
+private:
+  uint64_t val_;
+};
+
+class DynamicExpr : public ScriptExpr {
+public:
+  DynamicExpr(std::function<ExprValue()> impl)
+      : ScriptExpr(ExprKind::Dynamic), impl_(impl) {}
+  ExprValue getExprValue() const { return impl_(); }
+
+private:
+  std::function<ExprValue()> impl_;
+};
+
+class UnaryExpr : public ScriptExpr {
+public:
+  static const UnaryExpr *create();
+
+private:
+  UnaryExpr(StringRef op, ScriptExpr *operand)
+      : ScriptExpr(ExprKind::Unary), op_(op), operand_(operand) {}
+  StringRef op_;
+  const ScriptExpr *operand_;
+};
+
+class BinaryExpr : public ScriptExpr {
+public:
+  enum class Op {
+    Add,
+    Sub,
+    Mul,
+    Div,
+    Mod,
+    Shl,
+    Shr,
+    And,
+    Or,
+    Xor,
+    LAnd,
+    LOr,
+    Eq,
+    Neq,
+    Lt,
+    Gt,
+    Leq,
+    Geq,
+    AddAssign,
+    SubAssign,
+    MulAssign,
+    DivAssign,
+    ShlAssign,
+    ShrAssign,
+    AndAssign,
+    OrAssign,
+    XorAssign,
+    Invalid
+  };
+  BinaryExpr(StringRef op, ScriptExpr *LHS, ScriptExpr *RHS,
+             const std::string loc)
+      : ScriptExpr(ExprKind::Binary), LHS(LHS), RHS(RHS), loc_(loc) {
+    opcode = stringToOp(op);
----------------
PiJoules wrote:

nit:

```
ScriptExpr(ExprKind::Binary), opcode(stringToOp(op)), LHS(LHS), RHS(RHS), loc_(loc) {}
```

https://github.com/llvm/llvm-project/pull/106334