From 06159933d56fe4855fa06e05e2e67c2d000acbf1 Mon Sep 17 00:00:00 2001
From: Yujia Qiao <rapiz3142@gmail.com>
Date: Wed, 3 Nov 2021 16:25:04 +0800
Subject: [PATCH] support func prototype ( can use cstdlib now!)

---
 parser.cc  |  6 +++++-
 parser.h   |  2 +-
 visitor.cc | 14 +++++++++++---
 3 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/parser.cc b/parser.cc
index a260a17..eb2b44e 100644
--- a/parser.cc
+++ b/parser.cc
@@ -322,7 +322,11 @@ FunDecl* Parser::funDecl(Type retType, Token id) {
 
   consume(RIGHT_PAREN, "Expect `)` as argument list ends");
 
-  BlockStmt* b = blockStmt();
+  BlockStmt* b = nullptr;
+  if (match(1, LEFT_BRACE))
+    b = blockStmt();
+  else
+    consume(SEMICOLON, "Expect `,` after function prototype");
 
   return new FunDecl(id.lexeme, a, b, retType);
 }
diff --git a/parser.h b/parser.h
index 6dec2f1..8ec6bda 100644
--- a/parser.h
+++ b/parser.h
@@ -33,7 +33,7 @@ class Parser {
   VarDecl* varDecl(Type type, Token id);  // TYPE ('['SIZE']')? IDENTIFIER
                                           // (EQUAL EXPRESSION)? ;
   FunDecl* funDecl(Type type,
-                   Token id);  // TYPE IDENTIFIER '(' ARGS? ')' BLOCK
+                   Token id);  // TYPE IDENTIFIER '(' ARGS? ')' BLOCK?
   Args args();                 // TYPE ID (, TYPE ID)*
   RealArgs real_args();        // EXPR (, EXPR)*
 
diff --git a/visitor.cc b/visitor.cc
index e75a34b..e802e7e 100644
--- a/visitor.cc
+++ b/visitor.cc
@@ -268,7 +268,7 @@ void CodeGenVisitor::visit(VarDecl* st) {
 void CodeGenVisitor::visit(FunDecl* st) {
   if (scope.isWrapped()) abortMsg("nested function is forbidden");
   llvm::Function* F = l.mod->getFunction(st->identifier);
-  if (F) abortMsg("redefine func");
+  if (F && !F->empty()) abortMsg("redefine func");
 
   std::vector<llvm::Type*> args;
   for (auto [type, token] : st->args) {
@@ -281,6 +281,15 @@ void CodeGenVisitor::visit(FunDecl* st) {
 
   F = llvm::Function::Create(FT, llvm::Function::ExternalLinkage,
                              st->identifier, l.mod.get());
+  if (st->body == nullptr) {  // a prototype
+    size_t i = 0;
+    for (auto& a : F->args()) {
+      FormalArg formal = st->args[i++];
+      std::string name = formal.token.lexeme;
+      a.setName(name);
+    }
+    return;
+  }
 
   // Create a new basic block to start insertion into.
   llvm::BasicBlock* BB = llvm::BasicBlock::Create(*l.ctx, st->identifier, F);
@@ -302,8 +311,7 @@ void CodeGenVisitor::visit(FunDecl* st) {
   }
 
   v.visit(st->body);
-  if (llvm::verifyFunction(*F, &llvm::errs()))
-    ;  // abortMsg("verify error");
+  if (llvm::verifyFunction(*F, &llvm::errs())) abortMsg("verify error");
   // F->eraseFromParent();
 }
 void CodeGenVisitor::visit(BlockStmt* st) {