Add dereference operator

src/ast.cpp

@@ -80,6 +80,7 @@ std::string opstr(Unop &unop)
   switch (unop.op) {
     case bpftrace::Parser::token::LNOT: return "!";
     case bpftrace::Parser::token::BNOT: return "~";
+    case bpftrace::Parser::token::MUL:  return "dereference";
     default: abort();
   }
 }

src/codegen_llvm.cpp

@@ -124,6 +124,13 @@ void CodegenLLVM::visit(Unop &unop)
   switch (unop.op) {
     case bpftrace::Parser::token::LNOT: expr_ = b_.CreateNot(expr_); break;
     case bpftrace::Parser::token::BNOT: expr_ = b_.CreateNeg(expr_); break;
+    case bpftrace::Parser::token::MUL:
+    {
+      AllocaInst *dst = b_.CreateAllocaBPF();
+      b_.CreateProbeRead(dst, b_.getInt64(8), expr_);
+      expr_ = b_.CreateLoad(dst);
+      break;
+    }
     default: abort();
   }
 }

src/parser.yy

@@ -148,6 +148,7 @@ expr : INT             { $$ = new ast::Integer($1); }
      | expr BXOR expr  { $$ = new ast::Binop($1, token::BXOR,  $3); }
      | LNOT expr       { $$ = new ast::Unop(token::LNOT, $2); }
      | BNOT expr       { $$ = new ast::Unop(token::BNOT, $2); }
+     | MUL  expr       { $$ = new ast::Unop(token::MUL,  $2); }
      ;
 
 call : IDENT "(" ")"       { $$ = new ast::Call($1); }

src/semantic_analyser.cpp

@@ -142,6 +142,11 @@ void SemanticAnalyser::visit(Binop &binop)
 void SemanticAnalyser::visit(Unop &unop)
 {
   unop.expr->accept(*this);
+
+  if (type_ != Type::integer) {
+    err_ << "The " << opstr(unop) << " operator can not be used on expressions of type " << type_ << std::endl;
+  }
+
   type_ = Type::integer;
 }