7. 万花筒：扩展语言：可变变量¶
7.1. 第 7 章 简介¶
欢迎来到“使用 LLVM 实现语言”教程的第 7 章。在第 1 章到第 6 章中，我们构建了一个非常令人尊敬的，尽管简单，函数式编程语言。在我们的学习过程中，我们学习了一些解析技术，如何构建和表示 AST，如何构建 LLVM IR，以及如何优化生成的代码以及 JIT 编译它。
虽然万花筒作为一种函数式语言很有趣，但它作为函数式语言的事实使得为其生成 LLVM IR“过于简单”。特别是，函数式语言使得直接在SSA 形式中构建 LLVM IR 变得非常容易。由于 LLVM 要求输入代码为 SSA 形式，因此这是一个非常好的特性，并且对于新手来说，如何为具有可变变量的命令式语言生成代码通常并不清楚。
本章的简短（且令人高兴的）总结是，您的前端无需构建 SSA 形式：LLVM 为此提供了高度调整和经过良好测试的支持，尽管其工作方式对于某些人来说有点出乎意料。
7.2. 为什么这是一个难题？¶
要理解为什么可变变量会导致 SSA 构建复杂化，请考虑以下极其简单的 C 示例
int G, H;
int test(_Bool Condition) {
int X;
if (Condition)
X = G;
else
X = H;
return X;
}
在这种情况下，我们有变量“X”，其值取决于程序中执行的路径。由于在 return 指令之前 X 有两个不同的可能值，因此插入了一个 PHI 节点来合并这两个值。我们希望为此示例获得的 LLVM IR 如下所示
@G = weak global i32 0 ; type of @G is i32*
@H = weak global i32 0 ; type of @H is i32*
define i32 @test(i1 %Condition) {
entry:
br i1 %Condition, label %cond_true, label %cond_false
cond_true:
%X.0 = load i32, i32* @G
br label %cond_next
cond_false:
%X.1 = load i32, i32* @H
br label %cond_next
cond_next:
%X.2 = phi i32 [ %X.1, %cond_false ], [ %X.0, %cond_true ]
ret i32 %X.2
}
在此示例中，来自 G 和 H 全局变量的加载在 LLVM IR 中是显式的，并且它们位于 if 语句（cond_true/cond_false）的 then/else 分支中。为了合并传入的值，cond_next 块中的 X.2 phi 节点根据控制流来自何处选择要使用哪个值：如果控制流来自 cond_false 块，则 X.2 获取 X.1 的值。或者，如果控制流来自 cond_true，则它获取 X.0 的值。本章的意图不是解释 SSA 形式的细节。有关更多信息，请参阅众多在线参考之一。
本文的问题是“在将赋值降低到可变变量时，谁放置 phi 节点？”。这里的问题是 LLVM *要求*其 IR 为 SSA 形式：它没有“非 ssa”模式。但是，SSA 构建需要非平凡的算法和数据结构，因此每个前端都必须复制此逻辑是不方便且浪费的。
7.3. LLVM 中的内存¶
这里的“技巧”是，虽然 LLVM 确实要求所有寄存器值都为 SSA 形式，但它不要求（或允许）内存对象为 SSA 形式。在上面的示例中，请注意，来自 G 和 H 的加载是对 G 和 H 的直接访问：它们没有重命名或版本化。这与某些其他编译器系统不同，这些系统确实尝试对内存对象进行版本化。在 LLVM 中，它不是将内存的数据流分析编码到 LLVM IR 中，而是通过分析传递处理，这些传递是在需要时计算的。
考虑到这一点，高级思想是我们希望为函数中的每个可变对象创建一个堆栈变量（它位于内存中，因为它位于堆栈上）。为了利用这个技巧，我们需要讨论 LLVM 如何表示堆栈变量。
在 LLVM 中，所有内存访问都使用 load/store 指令明确表示，并且它被精心设计为不具有（或不需要）“取地址”运算符。请注意 @G/@H 全局变量的类型实际上是“i32*”，即使变量被定义为“i32”。这意味着 @G 在全局数据区域中定义了 i32 的*空间*，但其*名称*实际上指的是该空间的地址。堆栈变量的工作方式相同，只是它们不是使用全局变量定义声明，而是使用LLVM alloca 指令声明
define i32 @example() {
entry:
%X = alloca i32 ; type of %X is i32*.
...
%tmp = load i32, i32* %X ; load the stack value %X from the stack.
%tmp2 = add i32 %tmp, 1 ; increment it
store i32 %tmp2, i32* %X ; store it back
...
此代码显示了如何在 LLVM IR 中声明和操作堆栈变量的示例。使用 alloca 指令分配的堆栈内存是完全通用的：您可以将堆栈槽的地址传递给函数，可以将其存储在其他变量中，等等。在我们上面的示例中，我们可以重写该示例以使用 alloca 技术来避免使用 PHI 节点
@G = weak global i32 0 ; type of @G is i32*
@H = weak global i32 0 ; type of @H is i32*
define i32 @test(i1 %Condition) {
entry:
%X = alloca i32 ; type of %X is i32*.
br i1 %Condition, label %cond_true, label %cond_false
cond_true:
%X.0 = load i32, i32* @G
store i32 %X.0, i32* %X ; Update X
br label %cond_next
cond_false:
%X.1 = load i32, i32* @H
store i32 %X.1, i32* %X ; Update X
br label %cond_next
cond_next:
%X.2 = load i32, i32* %X ; Read X
ret i32 %X.2
}
这样，我们就发现了一种处理任意可变变量的方法，而无需创建 Phi 节点。
每个可变变量都成为一个堆栈分配。
变量的每次读取都成为来自堆栈的加载。
变量的每次更新都成为对堆栈的存储。
获取变量的地址直接使用堆栈地址。
虽然此解决方案解决了我们的直接问题，但它引入了另一个问题：我们现在显然为非常简单和常见的操作引入了大量堆栈流量，这是一个主要的性能问题。幸运的是，LLVM 优化器有一个高度调整的优化传递名为“mem2reg”，它处理这种情况，将像这样的 alloca 提升到 SSA 寄存器，并在适当的时候插入 Phi 节点。例如，如果您将此示例通过传递运行，您将获得
$ llvm-as < example.ll | opt -passes=mem2reg | llvm-dis
@G = weak global i32 0
@H = weak global i32 0
define i32 @test(i1 %Condition) {
entry:
br i1 %Condition, label %cond_true, label %cond_false
cond_true:
%X.0 = load i32, i32* @G
br label %cond_next
cond_false:
%X.1 = load i32, i32* @H
br label %cond_next
cond_next:
%X.01 = phi i32 [ %X.1, %cond_false ], [ %X.0, %cond_true ]
ret i32 %X.01
}
mem2reg 传递实现了构建 SSA 形式的标准“迭代支配边界”算法，并且具有一系列优化，可以加快（非常常见）退化情况的速度。mem2reg 优化传递是处理可变变量的答案，我们强烈建议您依赖它。请注意，mem2reg 仅在某些情况下适用于变量
mem2reg 是 alloca 驱动的：它查找 alloca，如果它可以处理它们，它会提升它们。它不适用于全局变量或堆分配。
mem2reg 仅查找函数入口块中的 alloca 指令。位于入口块保证 alloca 只执行一次，这使得分析更简单。
mem2reg 仅提升其用途为直接加载和存储的 alloca。如果堆栈对象的地址传递给函数，或者涉及任何奇怪的指针算术，则 alloca 不会被提升。
mem2reg 仅适用于第一类值（例如指针、标量和向量）的 alloca，并且仅当分配的数组大小为 1（或在 .ll 文件中缺失）时。mem2reg 无法将结构或数组提升到寄存器。请注意，“sroa”传递功能更强大，可以在许多情况下提升结构、“联合”和数组。
对于大多数命令式语言，所有这些属性都很容易满足，我们将在下面使用万花筒进行说明。您可能提出的最后一个问题是：我是否应该为我的前端费心处理这种胡说八道？如果我直接进行 SSA 构建，避免使用 mem2reg 优化传递，会不会更好？简而言之，我们强烈建议您使用此技术构建 SSA 形式，除非有充分的理由不这样做。使用此技术是
经过验证和良好测试：clang 对局部可变变量使用此技术。因此，LLVM 的最常见客户端正在使用它来处理大部分变量。您可以确保错误被快速发现并尽早修复。
极其快速：mem2reg 具有许多特殊情况，使其在常见情况下快速且完全通用。例如，它对仅在一个块中使用的变量、只有一个赋值点的变量、避免插入不必要的 phi 节点的良好启发式方法等具有快速路径。
调试信息生成所必需：LLVM 中的调试信息依赖于公开变量的地址，以便可以将调试信息附加到它。此技术与这种调试信息样式非常自然地吻合。
如果没有其他原因，这使得更容易让您的前端启动并运行，并且非常简单易于实现。现在让我们用可变变量扩展万花筒吧！
7.4. 万花筒中的可变变量¶
既然我们知道了要解决的问题类型，让我们看看在我们的小型万花筒语言的上下文中它是什么样子。我们将添加两个功能
使用“=”运算符变异变量的能力。
定义新变量的能力。
虽然第一项是本文的重点，但我们只有输入参数以及归纳变量的变量，并且重新定义它们只能达到一定程度:)。此外，无论您是否要对其进行变异，定义新变量的能力都是一项有用的功能。以下是一个激励示例，展示了我们如何使用这些
# Define ':' for sequencing: as a low-precedence operator that ignores operands
# and just returns the RHS.
def binary : 1 (x y) y;
# Recursive fib, we could do this before.
def fib(x)
if (x < 3) then
1
else
fib(x-1)+fib(x-2);
# Iterative fib.
def fibi(x)
var a = 1, b = 1, c in
(for i = 3, i < x in
c = a + b :
a = b :
b = c) :
b;
# Call it.
fibi(10);
为了变异变量，我们必须更改我们现有的变量以使用“alloca 技巧”。一旦我们有了它，我们将添加新的运算符，然后扩展万花筒以支持新的变量定义。
7.5. 调整现有变量以进行变异¶
万花筒中的符号表在代码生成时由‘NamedValues’映射管理。此映射当前跟踪保存命名变量的双精度值的 LLVM“Value*”。为了支持变异，我们需要稍微更改它，以便NamedValues保存相关变量的*内存位置*。请注意，此更改是重构：它更改了代码的结构，但（本身）不会更改编译器的行为。所有这些更改都隔离在万花筒代码生成器中。
在 Kaleidoscope 的开发过程中，目前它只支持两种变量：函数的传入参数和 'for' 循环的循环变量。为了保持一致性，除了其他用户定义的变量外，我们还将允许修改这些变量。这意味着它们都需要内存位置。
为了开始转换 Kaleidoscope，我们将更改 NamedValues 映射，使其映射到 AllocaInst* 而不是 Value*。完成此操作后，C++ 编译器会告诉我们需要更新代码的哪些部分。
static std::map<std::string, AllocaInst*> NamedValues;
此外，由于我们需要创建这些 alloca，我们将使用一个辅助函数来确保在函数的入口块中创建这些 alloca。
/// CreateEntryBlockAlloca - Create an alloca instruction in the entry block of
/// the function. This is used for mutable variables etc.
static AllocaInst *CreateEntryBlockAlloca(Function *TheFunction,
const std::string &VarName) {
IRBuilder<> TmpB(&TheFunction->getEntryBlock(),
TheFunction->getEntryBlock().begin());
return TmpB.CreateAlloca(Type::getDoubleTy(*TheContext), nullptr,
VarName);
}
这段看起来有点奇怪的代码创建了一个 IRBuilder 对象，该对象指向入口块的第一个指令 (.begin())。然后它使用预期的名称创建一个 alloca 并返回它。因为 Kaleidoscope 中的所有值都是双精度浮点数，所以无需传入要使用的类型。
有了这个，我们想要做的第一个功能更改与变量引用有关。在我们的新方案中，变量驻留在堆栈上，因此生成对它们的引用的代码实际上需要生成来自堆栈槽的加载。
Value *VariableExprAST::codegen() {
// Look this variable up in the function.
AllocaInst *A = NamedValues[Name];
if (!A)
return LogErrorV("Unknown variable name");
// Load the value.
return Builder->CreateLoad(A->getAllocatedType(), A, Name.c_str());
}
如您所见，这非常简单。现在我们需要更新定义变量的内容以设置 alloca。我们将从 ForExprAST::codegen() 开始（有关完整代码，请参阅完整代码列表）。
Function *TheFunction = Builder->GetInsertBlock()->getParent();
// Create an alloca for the variable in the entry block.
AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
// Emit the start code first, without 'variable' in scope.
Value *StartVal = Start->codegen();
if (!StartVal)
return nullptr;
// Store the value into the alloca.
Builder->CreateStore(StartVal, Alloca);
...
// Compute the end condition.
Value *EndCond = End->codegen();
if (!EndCond)
return nullptr;
// Reload, increment, and restore the alloca. This handles the case where
// the body of the loop mutates the variable.
Value *CurVar = Builder->CreateLoad(Alloca->getAllocatedType(), Alloca,
VarName.c_str());
Value *NextVar = Builder->CreateFAdd(CurVar, StepVal, "nextvar");
Builder->CreateStore(NextVar, Alloca);
...
此代码与我们允许可变变量之前的代码几乎相同。最大的区别是我们不再需要构造 PHI 节点，并且我们使用 load/store 根据需要访问变量。
为了支持可变参数变量，我们还需要为它们创建 alloca。此代码也很简单。
Function *FunctionAST::codegen() {
...
Builder->SetInsertPoint(BB);
// Record the function arguments in the NamedValues map.
NamedValues.clear();
for (auto &Arg : TheFunction->args()) {
// Create an alloca for this variable.
AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, Arg.getName());
// Store the initial value into the alloca.
Builder->CreateStore(&Arg, Alloca);
// Add arguments to variable symbol table.
NamedValues[std::string(Arg.getName())] = Alloca;
}
if (Value *RetVal = Body->codegen()) {
...
对于每个参数，我们创建一个 alloca，将输入值存储到函数的 alloca 中，并将 alloca 注册为参数的内存位置。此方法由 FunctionAST::codegen() 在它设置函数的入口块之后立即调用。
最后缺失的部分是添加 mem2reg 传递，这使我们能够再次获得良好的代码生成。
// Promote allocas to registers.
TheFPM->add(createPromoteMemoryToRegisterPass());
// Do simple "peephole" optimizations and bit-twiddling optzns.
TheFPM->add(createInstructionCombiningPass());
// Reassociate expressions.
TheFPM->add(createReassociatePass());
...
看看 mem2reg 优化运行前后代码的样子很有趣。例如，这是我们递归 fib 函数的运行前/后的代码。优化前
define double @fib(double %x) {
entry:
%x1 = alloca double
store double %x, double* %x1
%x2 = load double, double* %x1
%cmptmp = fcmp ult double %x2, 3.000000e+00
%booltmp = uitofp i1 %cmptmp to double
%ifcond = fcmp one double %booltmp, 0.000000e+00
br i1 %ifcond, label %then, label %else
then: ; preds = %entry
br label %ifcont
else: ; preds = %entry
%x3 = load double, double* %x1
%subtmp = fsub double %x3, 1.000000e+00
%calltmp = call double @fib(double %subtmp)
%x4 = load double, double* %x1
%subtmp5 = fsub double %x4, 2.000000e+00
%calltmp6 = call double @fib(double %subtmp5)
%addtmp = fadd double %calltmp, %calltmp6
br label %ifcont
ifcont: ; preds = %else, %then
%iftmp = phi double [ 1.000000e+00, %then ], [ %addtmp, %else ]
ret double %iftmp
}
这里只有一个变量（x，输入参数），但您仍然可以看到我们正在使用的极其简单的代码生成策略。在入口块中，创建一个 alloca，并将初始输入值存储到其中。对变量的每个引用都会从堆栈中重新加载。此外，请注意我们没有修改 if/then/else 表达式，因此它仍然插入 PHI 节点。虽然我们可以为它创建一个 alloca，但实际上为它创建一个 PHI 节点更容易，所以我们仍然只是创建 PHI。
这是 mem2reg 传递运行后的代码
define double @fib(double %x) {
entry:
%cmptmp = fcmp ult double %x, 3.000000e+00
%booltmp = uitofp i1 %cmptmp to double
%ifcond = fcmp one double %booltmp, 0.000000e+00
br i1 %ifcond, label %then, label %else
then:
br label %ifcont
else:
%subtmp = fsub double %x, 1.000000e+00
%calltmp = call double @fib(double %subtmp)
%subtmp5 = fsub double %x, 2.000000e+00
%calltmp6 = call double @fib(double %subtmp5)
%addtmp = fadd double %calltmp, %calltmp6
br label %ifcont
ifcont: ; preds = %else, %then
%iftmp = phi double [ 1.000000e+00, %then ], [ %addtmp, %else ]
ret double %iftmp
}
对于 mem2reg 来说，这是一个简单的案例，因为变量没有重新定义。展示这一点的目的是缓解您对插入如此明显的低效代码的担忧：)。
在其余优化器运行后，我们得到
define double @fib(double %x) {
entry:
%cmptmp = fcmp ult double %x, 3.000000e+00
%booltmp = uitofp i1 %cmptmp to double
%ifcond = fcmp ueq double %booltmp, 0.000000e+00
br i1 %ifcond, label %else, label %ifcont
else:
%subtmp = fsub double %x, 1.000000e+00
%calltmp = call double @fib(double %subtmp)
%subtmp5 = fsub double %x, 2.000000e+00
%calltmp6 = call double @fib(double %subtmp5)
%addtmp = fadd double %calltmp, %calltmp6
ret double %addtmp
ifcont:
ret double 1.000000e+00
}
在这里，我们看到 simplifycfg 传递决定将 return 指令克隆到 'else' 块的末尾。这允许它消除一些分支和 PHI 节点。
现在所有符号表引用都已更新为使用堆栈变量，我们将添加赋值运算符。
7.6. 新的赋值运算符¶
在我们当前的框架下，添加新的赋值运算符非常简单。我们将像处理任何其他二元运算符一样解析它，但在内部处理它（而不是允许用户定义它）。第一步是设置优先级
int main() {
// Install standard binary operators.
// 1 is lowest precedence.
BinopPrecedence['='] = 2;
BinopPrecedence['<'] = 10;
BinopPrecedence['+'] = 20;
BinopPrecedence['-'] = 20;
现在解析器知道二元运算符的优先级，它会处理所有解析和 AST 生成。我们只需要为赋值运算符实现代码生成。如下所示
Value *BinaryExprAST::codegen() {
// Special case '=' because we don't want to emit the LHS as an expression.
if (Op == '=') {
// This assume we're building without RTTI because LLVM builds that way by
// default. If you build LLVM with RTTI this can be changed to a
// dynamic_cast for automatic error checking.
VariableExprAST *LHSE = static_cast<VariableExprAST*>(LHS.get());
if (!LHSE)
return LogErrorV("destination of '=' must be a variable");
与其他二元运算符不同，我们的赋值运算符不遵循“发出 LHS，发出 RHS，进行计算”模型。因此，它在处理其他二元运算符之前作为特殊情况进行处理。另一件奇怪的事情是它要求 LHS 是一个变量。“(x+1) = expr” 是无效的 - 只有像“x = expr”这样的东西是允许的。
// Codegen the RHS.
Value *Val = RHS->codegen();
if (!Val)
return nullptr;
// Look up the name.
Value *Variable = NamedValues[LHSE->getName()];
if (!Variable)
return LogErrorV("Unknown variable name");
Builder->CreateStore(Val, Variable);
return Val;
}
...
一旦我们有了变量，赋值的代码生成就很简单了：我们发出赋值的 RHS，创建一个存储，并返回计算出的值。返回值允许像“X = (Y = Z)”这样的链式赋值。
现在我们有了赋值运算符，我们可以修改循环变量和参数。例如，我们现在可以运行如下代码
# Function to print a double.
extern printd(x);
# Define ':' for sequencing: as a low-precedence operator that ignores operands
# and just returns the RHS.
def binary : 1 (x y) y;
def test(x)
printd(x) :
x = 4 :
printd(x);
test(123);
运行时，此示例打印“123”，然后打印“4”，表明我们确实修改了值！好的，我们现在正式实现了我们的目标：使其工作需要在一般情况下进行 SSA 构造。但是，为了真正有用，我们希望能够定义我们自己的局部变量，让我们接下来添加它！
7.7. 用户定义的局部变量¶
添加 var/in 就像我们对 Kaleidoscope 做的任何其他扩展一样：我们扩展了词法分析器、解析器、AST 和代码生成器。添加新的 'var/in' 结构的第一步是扩展词法分析器。和以前一样，这非常简单，代码如下所示
enum Token {
...
// var definition
tok_var = -13
...
}
...
static int gettok() {
...
if (IdentifierStr == "in")
return tok_in;
if (IdentifierStr == "binary")
return tok_binary;
if (IdentifierStr == "unary")
return tok_unary;
if (IdentifierStr == "var")
return tok_var;
return tok_identifier;
...
下一步是定义我们将构造的 AST 节点。对于 var/in，它看起来像这样
/// VarExprAST - Expression class for var/in
class VarExprAST : public ExprAST {
std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames;
std::unique_ptr<ExprAST> Body;
public:
VarExprAST(std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames,
std::unique_ptr<ExprAST> Body)
: VarNames(std::move(VarNames)), Body(std::move(Body)) {}
Value *codegen() override;
};
var/in 允许一次定义多个名称列表，并且每个名称可以选择具有初始化值。因此，我们在 VarNames 向量中捕获此信息。此外，var/in 还有一个主体，该主体允许访问 var/in 定义的变量。
有了这个，我们可以定义解析器部分。我们首先将其添加为主表达式
/// primary
/// ::= identifierexpr
/// ::= numberexpr
/// ::= parenexpr
/// ::= ifexpr
/// ::= forexpr
/// ::= varexpr
static std::unique_ptr<ExprAST> ParsePrimary() {
switch (CurTok) {
default:
return LogError("unknown token when expecting an expression");
case tok_identifier:
return ParseIdentifierExpr();
case tok_number:
return ParseNumberExpr();
case '(':
return ParseParenExpr();
case tok_if:
return ParseIfExpr();
case tok_for:
return ParseForExpr();
case tok_var:
return ParseVarExpr();
}
}
接下来我们定义 ParseVarExpr
/// varexpr ::= 'var' identifier ('=' expression)?
// (',' identifier ('=' expression)?)* 'in' expression
static std::unique_ptr<ExprAST> ParseVarExpr() {
getNextToken(); // eat the var.
std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames;
// At least one variable name is required.
if (CurTok != tok_identifier)
return LogError("expected identifier after var");
这段代码的第一部分将标识符/表达式对列表解析到本地 VarNames 向量中。
while (true) {
std::string Name = IdentifierStr;
getNextToken(); // eat identifier.
// Read the optional initializer.
std::unique_ptr<ExprAST> Init;
if (CurTok == '=') {
getNextToken(); // eat the '='.
Init = ParseExpression();
if (!Init) return nullptr;
}
VarNames.push_back(std::make_pair(Name, std::move(Init)));
// End of var list, exit loop.
if (CurTok != ',') break;
getNextToken(); // eat the ','.
if (CurTok != tok_identifier)
return LogError("expected identifier list after var");
}
解析完所有变量后，我们解析主体并创建 AST 节点
// At this point, we have to have 'in'.
if (CurTok != tok_in)
return LogError("expected 'in' keyword after 'var'");
getNextToken(); // eat 'in'.
auto Body = ParseExpression();
if (!Body)
return nullptr;
return std::make_unique<VarExprAST>(std::move(VarNames),
std::move(Body));
}
现在我们可以解析和表示代码了，我们需要支持为它发出 LLVM IR。此代码从以下内容开始
Value *VarExprAST::codegen() {
std::vector<AllocaInst *> OldBindings;
Function *TheFunction = Builder->GetInsertBlock()->getParent();
// Register all variables and emit their initializer.
for (unsigned i = 0, e = VarNames.size(); i != e; ++i) {
const std::string &VarName = VarNames[i].first;
ExprAST *Init = VarNames[i].second.get();
基本上它循环遍历所有变量，一次安装一个。对于我们放入符号表中的每个变量，我们都会记住我们在 OldBindings 中替换的先前值。
// Emit the initializer before adding the variable to scope, this prevents
// the initializer from referencing the variable itself, and permits stuff
// like this:
// var a = 1 in
// var a = a in ... # refers to outer 'a'.
Value *InitVal;
if (Init) {
InitVal = Init->codegen();
if (!InitVal)
return nullptr;
} else { // If not specified, use 0.0.
InitVal = ConstantFP::get(*TheContext, APFloat(0.0));
}
AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
Builder->CreateStore(InitVal, Alloca);
// Remember the old variable binding so that we can restore the binding when
// we unrecurse.
OldBindings.push_back(NamedValues[VarName]);
// Remember this binding.
NamedValues[VarName] = Alloca;
}
这里注释比代码多。基本思想是我们发出初始化程序，创建 alloca，然后更新符号表以指向它。一旦所有变量都安装到符号表中，我们就评估 var/in 表达式的正文
// Codegen the body, now that all vars are in scope.
Value *BodyVal = Body->codegen();
if (!BodyVal)
return nullptr;
最后，在返回之前，我们恢复先前的变量绑定
// Pop all our variables from scope.
for (unsigned i = 0, e = VarNames.size(); i != e; ++i)
NamedValues[VarNames[i].first] = OldBindings[i];
// Return the body computation.
return BodyVal;
}
所有这些的最终结果是我们获得了正确作用域的变量定义，并且我们甚至（微不足道地）允许修改它们：)。
至此，我们完成了我们设定的目标。我们从介绍中得到的漂亮的迭代 fib 示例可以正常编译和运行。mem2reg 传递将我们所有的堆栈变量优化为 SSA 寄存器，在需要的地方插入 PHI 节点，并且我们的前端仍然很简单：在任何地方都看不到“迭代支配边界”计算。
7.8. 完整代码列表¶
这是我们正在运行的示例的完整代码列表，增强了可变变量和 var/in 支持。要构建此示例，请使用
# Compile
clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core orcjit native` -O3 -o toy
# Run
./toy
代码如下
#include "../include/KaleidoscopeJIT.h"
#include "llvm/ADT/APFloat.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Verifier.h"
#include "llvm/Passes/PassBuilder.h"
#include "llvm/Passes/StandardInstrumentations.h"
#include "llvm/Support/TargetSelect.h"
#include "llvm/Target/TargetMachine.h"
#include "llvm/Transforms/InstCombine/InstCombine.h"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Transforms/Scalar/GVN.h"
#include "llvm/Transforms/Scalar/Reassociate.h"
#include "llvm/Transforms/Scalar/SimplifyCFG.h"
#include "llvm/Transforms/Utils.h"
#include <algorithm>
#include <cassert>
#include <cctype>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <map>
#include <memory>
#include <string>
#include <utility>
#include <vector>
using namespace llvm;
using namespace llvm::orc;
//===----------------------------------------------------------------------===//
// Lexer
//===----------------------------------------------------------------------===//
// The lexer returns tokens [0-255] if it is an unknown character, otherwise one
// of these for known things.
enum Token {
tok_eof = -1,
// commands
tok_def = -2,
tok_extern = -3,
// primary
tok_identifier = -4,
tok_number = -5,
// control
tok_if = -6,
tok_then = -7,
tok_else = -8,
tok_for = -9,
tok_in = -10,
// operators
tok_binary = -11,
tok_unary = -12,
// var definition
tok_var = -13
};
static std::string IdentifierStr; // Filled in if tok_identifier
static double NumVal; // Filled in if tok_number
/// gettok - Return the next token from standard input.
static int gettok() {
static int LastChar = ' ';
// Skip any whitespace.
while (isspace(LastChar))
LastChar = getchar();
if (isalpha(LastChar)) { // identifier: [a-zA-Z][a-zA-Z0-9]*
IdentifierStr = LastChar;
while (isalnum((LastChar = getchar())))
IdentifierStr += LastChar;
if (IdentifierStr == "def")
return tok_def;
if (IdentifierStr == "extern")
return tok_extern;
if (IdentifierStr == "if")
return tok_if;
if (IdentifierStr == "then")
return tok_then;
if (IdentifierStr == "else")
return tok_else;
if (IdentifierStr == "for")
return tok_for;
if (IdentifierStr == "in")
return tok_in;
if (IdentifierStr == "binary")
return tok_binary;
if (IdentifierStr == "unary")
return tok_unary;
if (IdentifierStr == "var")
return tok_var;
return tok_identifier;
}
if (isdigit(LastChar) || LastChar == '.') { // Number: [0-9.]+
std::string NumStr;
do {
NumStr += LastChar;
LastChar = getchar();
} while (isdigit(LastChar) || LastChar == '.');
NumVal = strtod(NumStr.c_str(), nullptr);
return tok_number;
}
if (LastChar == '#') {
// Comment until end of line.
do
LastChar = getchar();
while (LastChar != EOF && LastChar != '\n' && LastChar != '\r');
if (LastChar != EOF)
return gettok();
}
// Check for end of file. Don't eat the EOF.
if (LastChar == EOF)
return tok_eof;
// Otherwise, just return the character as its ascii value.
int ThisChar = LastChar;
LastChar = getchar();
return ThisChar;
}
//===----------------------------------------------------------------------===//
// Abstract Syntax Tree (aka Parse Tree)
//===----------------------------------------------------------------------===//
namespace {
/// ExprAST - Base class for all expression nodes.
class ExprAST {
public:
virtual ~ExprAST() = default;
virtual Value *codegen() = 0;
};
/// NumberExprAST - Expression class for numeric literals like "1.0".
class NumberExprAST : public ExprAST {
double Val;
public:
NumberExprAST(double Val) : Val(Val) {}
Value *codegen() override;
};
/// VariableExprAST - Expression class for referencing a variable, like "a".
class VariableExprAST : public ExprAST {
std::string Name;
public:
VariableExprAST(const std::string &Name) : Name(Name) {}
Value *codegen() override;
const std::string &getName() const { return Name; }
};
/// UnaryExprAST - Expression class for a unary operator.
class UnaryExprAST : public ExprAST {
char Opcode;
std::unique_ptr<ExprAST> Operand;
public:
UnaryExprAST(char Opcode, std::unique_ptr<ExprAST> Operand)
: Opcode(Opcode), Operand(std::move(Operand)) {}
Value *codegen() override;
};
/// BinaryExprAST - Expression class for a binary operator.
class BinaryExprAST : public ExprAST {
char Op;
std::unique_ptr<ExprAST> LHS, RHS;
public:
BinaryExprAST(char Op, std::unique_ptr<ExprAST> LHS,
std::unique_ptr<ExprAST> RHS)
: Op(Op), LHS(std::move(LHS)), RHS(std::move(RHS)) {}
Value *codegen() override;
};
/// CallExprAST - Expression class for function calls.
class CallExprAST : public ExprAST {
std::string Callee;
std::vector<std::unique_ptr<ExprAST>> Args;
public:
CallExprAST(const std::string &Callee,
std::vector<std::unique_ptr<ExprAST>> Args)
: Callee(Callee), Args(std::move(Args)) {}
Value *codegen() override;
};
/// IfExprAST - Expression class for if/then/else.
class IfExprAST : public ExprAST {
std::unique_ptr<ExprAST> Cond, Then, Else;
public:
IfExprAST(std::unique_ptr<ExprAST> Cond, std::unique_ptr<ExprAST> Then,
std::unique_ptr<ExprAST> Else)
: Cond(std::move(Cond)), Then(std::move(Then)), Else(std::move(Else)) {}
Value *codegen() override;
};
/// ForExprAST - Expression class for for/in.
class ForExprAST : public ExprAST {
std::string VarName;
std::unique_ptr<ExprAST> Start, End, Step, Body;
public:
ForExprAST(const std::string &VarName, std::unique_ptr<ExprAST> Start,
std::unique_ptr<ExprAST> End, std::unique_ptr<ExprAST> Step,
std::unique_ptr<ExprAST> Body)
: VarName(VarName), Start(std::move(Start)), End(std::move(End)),
Step(std::move(Step)), Body(std::move(Body)) {}
Value *codegen() override;
};
/// VarExprAST - Expression class for var/in
class VarExprAST : public ExprAST {
std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames;
std::unique_ptr<ExprAST> Body;
public:
VarExprAST(
std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames,
std::unique_ptr<ExprAST> Body)
: VarNames(std::move(VarNames)), Body(std::move(Body)) {}
Value *codegen() override;
};
/// PrototypeAST - This class represents the "prototype" for a function,
/// which captures its name, and its argument names (thus implicitly the number
/// of arguments the function takes), as well as if it is an operator.
class PrototypeAST {
std::string Name;
std::vector<std::string> Args;
bool IsOperator;
unsigned Precedence; // Precedence if a binary op.
public:
PrototypeAST(const std::string &Name, std::vector<std::string> Args,
bool IsOperator = false, unsigned Prec = 0)
: Name(Name), Args(std::move(Args)), IsOperator(IsOperator),
Precedence(Prec) {}
Function *codegen();
const std::string &getName() const { return Name; }
bool isUnaryOp() const { return IsOperator && Args.size() == 1; }
bool isBinaryOp() const { return IsOperator && Args.size() == 2; }
char getOperatorName() const {
assert(isUnaryOp() || isBinaryOp());
return Name[Name.size() - 1];
}
unsigned getBinaryPrecedence() const { return Precedence; }
};
/// FunctionAST - This class represents a function definition itself.
class FunctionAST {
std::unique_ptr<PrototypeAST> Proto;
std::unique_ptr<ExprAST> Body;
public:
FunctionAST(std::unique_ptr<PrototypeAST> Proto,
std::unique_ptr<ExprAST> Body)
: Proto(std::move(Proto)), Body(std::move(Body)) {}
Function *codegen();
};
} // end anonymous namespace
//===----------------------------------------------------------------------===//
// Parser
//===----------------------------------------------------------------------===//
/// CurTok/getNextToken - Provide a simple token buffer. CurTok is the current
/// token the parser is looking at. getNextToken reads another token from the
/// lexer and updates CurTok with its results.
static int CurTok;
static int getNextToken() { return CurTok = gettok(); }
/// BinopPrecedence - This holds the precedence for each binary operator that is
/// defined.
static std::map<char, int> BinopPrecedence;
/// GetTokPrecedence - Get the precedence of the pending binary operator token.
static int GetTokPrecedence() {
if (!isascii(CurTok))
return -1;
// Make sure it's a declared binop.
int TokPrec = BinopPrecedence[CurTok];
if (TokPrec <= 0)
return -1;
return TokPrec;
}
/// LogError* - These are little helper functions for error handling.
std::unique_ptr<ExprAST> LogError(const char *Str) {
fprintf(stderr, "Error: %s\n", Str);
return nullptr;
}
std::unique_ptr<PrototypeAST> LogErrorP(const char *Str) {
LogError(Str);
return nullptr;
}
static std::unique_ptr<ExprAST> ParseExpression();
/// numberexpr ::= number
static std::unique_ptr<ExprAST> ParseNumberExpr() {
auto Result = std::make_unique<NumberExprAST>(NumVal);
getNextToken(); // consume the number
return std::move(Result);
}
/// parenexpr ::= '(' expression ')'
static std::unique_ptr<ExprAST> ParseParenExpr() {
getNextToken(); // eat (.
auto V = ParseExpression();
if (!V)
return nullptr;
if (CurTok != ')')
return LogError("expected ')'");
getNextToken(); // eat ).
return V;
}
/// identifierexpr
/// ::= identifier
/// ::= identifier '(' expression* ')'
static std::unique_ptr<ExprAST> ParseIdentifierExpr() {
std::string IdName = IdentifierStr;
getNextToken(); // eat identifier.
if (CurTok != '(') // Simple variable ref.
return std::make_unique<VariableExprAST>(IdName);
// Call.
getNextToken(); // eat (
std::vector<std::unique_ptr<ExprAST>> Args;
if (CurTok != ')') {
while (true) {
if (auto Arg = ParseExpression())
Args.push_back(std::move(Arg));
else
return nullptr;
if (CurTok == ')')
break;
if (CurTok != ',')
return LogError("Expected ')' or ',' in argument list");
getNextToken();
}
}
// Eat the ')'.
getNextToken();
return std::make_unique<CallExprAST>(IdName, std::move(Args));
}
/// ifexpr ::= 'if' expression 'then' expression 'else' expression
static std::unique_ptr<ExprAST> ParseIfExpr() {
getNextToken(); // eat the if.
// condition.
auto Cond = ParseExpression();
if (!Cond)
return nullptr;
if (CurTok != tok_then)
return LogError("expected then");
getNextToken(); // eat the then
auto Then = ParseExpression();
if (!Then)
return nullptr;
if (CurTok != tok_else)
return LogError("expected else");
getNextToken();
auto Else = ParseExpression();
if (!Else)
return nullptr;
return std::make_unique<IfExprAST>(std::move(Cond), std::move(Then),
std::move(Else));
}
/// forexpr ::= 'for' identifier '=' expr ',' expr (',' expr)? 'in' expression
static std::unique_ptr<ExprAST> ParseForExpr() {
getNextToken(); // eat the for.
if (CurTok != tok_identifier)
return LogError("expected identifier after for");
std::string IdName = IdentifierStr;
getNextToken(); // eat identifier.
if (CurTok != '=')
return LogError("expected '=' after for");
getNextToken(); // eat '='.
auto Start = ParseExpression();
if (!Start)
return nullptr;
if (CurTok != ',')
return LogError("expected ',' after for start value");
getNextToken();
auto End = ParseExpression();
if (!End)
return nullptr;
// The step value is optional.
std::unique_ptr<ExprAST> Step;
if (CurTok == ',') {
getNextToken();
Step = ParseExpression();
if (!Step)
return nullptr;
}
if (CurTok != tok_in)
return LogError("expected 'in' after for");
getNextToken(); // eat 'in'.
auto Body = ParseExpression();
if (!Body)
return nullptr;
return std::make_unique<ForExprAST>(IdName, std::move(Start), std::move(End),
std::move(Step), std::move(Body));
}
/// varexpr ::= 'var' identifier ('=' expression)?
// (',' identifier ('=' expression)?)* 'in' expression
static std::unique_ptr<ExprAST> ParseVarExpr() {
getNextToken(); // eat the var.
std::vector<std::pair<std::string, std::unique_ptr<ExprAST>>> VarNames;
// At least one variable name is required.
if (CurTok != tok_identifier)
return LogError("expected identifier after var");
while (true) {
std::string Name = IdentifierStr;
getNextToken(); // eat identifier.
// Read the optional initializer.
std::unique_ptr<ExprAST> Init = nullptr;
if (CurTok == '=') {
getNextToken(); // eat the '='.
Init = ParseExpression();
if (!Init)
return nullptr;
}
VarNames.push_back(std::make_pair(Name, std::move(Init)));
// End of var list, exit loop.
if (CurTok != ',')
break;
getNextToken(); // eat the ','.
if (CurTok != tok_identifier)
return LogError("expected identifier list after var");
}
// At this point, we have to have 'in'.
if (CurTok != tok_in)
return LogError("expected 'in' keyword after 'var'");
getNextToken(); // eat 'in'.
auto Body = ParseExpression();
if (!Body)
return nullptr;
return std::make_unique<VarExprAST>(std::move(VarNames), std::move(Body));
}
/// primary
/// ::= identifierexpr
/// ::= numberexpr
/// ::= parenexpr
/// ::= ifexpr
/// ::= forexpr
/// ::= varexpr
static std::unique_ptr<ExprAST> ParsePrimary() {
switch (CurTok) {
default:
return LogError("unknown token when expecting an expression");
case tok_identifier:
return ParseIdentifierExpr();
case tok_number:
return ParseNumberExpr();
case '(':
return ParseParenExpr();
case tok_if:
return ParseIfExpr();
case tok_for:
return ParseForExpr();
case tok_var:
return ParseVarExpr();
}
}
/// unary
/// ::= primary
/// ::= '!' unary
static std::unique_ptr<ExprAST> ParseUnary() {
// If the current token is not an operator, it must be a primary expr.
if (!isascii(CurTok) || CurTok == '(' || CurTok == ',')
return ParsePrimary();
// If this is a unary operator, read it.
int Opc = CurTok;
getNextToken();
if (auto Operand = ParseUnary())
return std::make_unique<UnaryExprAST>(Opc, std::move(Operand));
return nullptr;
}
/// binoprhs
/// ::= ('+' unary)*
static std::unique_ptr<ExprAST> ParseBinOpRHS(int ExprPrec,
std::unique_ptr<ExprAST> LHS) {
// If this is a binop, find its precedence.
while (true) {
int TokPrec = GetTokPrecedence();
// If this is a binop that binds at least as tightly as the current binop,
// consume it, otherwise we are done.
if (TokPrec < ExprPrec)
return LHS;
// Okay, we know this is a binop.
int BinOp = CurTok;
getNextToken(); // eat binop
// Parse the unary expression after the binary operator.
auto RHS = ParseUnary();
if (!RHS)
return nullptr;
// If BinOp binds less tightly with RHS than the operator after RHS, let
// the pending operator take RHS as its LHS.
int NextPrec = GetTokPrecedence();
if (TokPrec < NextPrec) {
RHS = ParseBinOpRHS(TokPrec + 1, std::move(RHS));
if (!RHS)
return nullptr;
}
// Merge LHS/RHS.
LHS =
std::make_unique<BinaryExprAST>(BinOp, std::move(LHS), std::move(RHS));
}
}
/// expression
/// ::= unary binoprhs
///
static std::unique_ptr<ExprAST> ParseExpression() {
auto LHS = ParseUnary();
if (!LHS)
return nullptr;
return ParseBinOpRHS(0, std::move(LHS));
}
/// prototype
/// ::= id '(' id* ')'
/// ::= binary LETTER number? (id, id)
/// ::= unary LETTER (id)
static std::unique_ptr<PrototypeAST> ParsePrototype() {
std::string FnName;
unsigned Kind = 0; // 0 = identifier, 1 = unary, 2 = binary.
unsigned BinaryPrecedence = 30;
switch (CurTok) {
default:
return LogErrorP("Expected function name in prototype");
case tok_identifier:
FnName = IdentifierStr;
Kind = 0;
getNextToken();
break;
case tok_unary:
getNextToken();
if (!isascii(CurTok))
return LogErrorP("Expected unary operator");
FnName = "unary";
FnName += (char)CurTok;
Kind = 1;
getNextToken();
break;
case tok_binary:
getNextToken();
if (!isascii(CurTok))
return LogErrorP("Expected binary operator");
FnName = "binary";
FnName += (char)CurTok;
Kind = 2;
getNextToken();
// Read the precedence if present.
if (CurTok == tok_number) {
if (NumVal < 1 || NumVal > 100)
return LogErrorP("Invalid precedence: must be 1..100");
BinaryPrecedence = (unsigned)NumVal;
getNextToken();
}
break;
}
if (CurTok != '(')
return LogErrorP("Expected '(' in prototype");
std::vector<std::string> ArgNames;
while (getNextToken() == tok_identifier)
ArgNames.push_back(IdentifierStr);
if (CurTok != ')')
return LogErrorP("Expected ')' in prototype");
// success.
getNextToken(); // eat ')'.
// Verify right number of names for operator.
if (Kind && ArgNames.size() != Kind)
return LogErrorP("Invalid number of operands for operator");
return std::make_unique<PrototypeAST>(FnName, ArgNames, Kind != 0,
BinaryPrecedence);
}
/// definition ::= 'def' prototype expression
static std::unique_ptr<FunctionAST> ParseDefinition() {
getNextToken(); // eat def.
auto Proto = ParsePrototype();
if (!Proto)
return nullptr;
if (auto E = ParseExpression())
return std::make_unique<FunctionAST>(std::move(Proto), std::move(E));
return nullptr;
}
/// toplevelexpr ::= expression
static std::unique_ptr<FunctionAST> ParseTopLevelExpr() {
if (auto E = ParseExpression()) {
// Make an anonymous proto.
auto Proto = std::make_unique<PrototypeAST>("__anon_expr",
std::vector<std::string>());
return std::make_unique<FunctionAST>(std::move(Proto), std::move(E));
}
return nullptr;
}
/// external ::= 'extern' prototype
static std::unique_ptr<PrototypeAST> ParseExtern() {
getNextToken(); // eat extern.
return ParsePrototype();
}
//===----------------------------------------------------------------------===//
// Code Generation
//===----------------------------------------------------------------------===//
static std::unique_ptr<LLVMContext> TheContext;
static std::unique_ptr<Module> TheModule;
static std::unique_ptr<IRBuilder<>> Builder;
static std::map<std::string, AllocaInst *> NamedValues;
static std::unique_ptr<KaleidoscopeJIT> TheJIT;
static std::unique_ptr<FunctionPassManager> TheFPM;
static std::unique_ptr<LoopAnalysisManager> TheLAM;
static std::unique_ptr<FunctionAnalysisManager> TheFAM;
static std::unique_ptr<CGSCCAnalysisManager> TheCGAM;
static std::unique_ptr<ModuleAnalysisManager> TheMAM;
static std::unique_ptr<PassInstrumentationCallbacks> ThePIC;
static std::unique_ptr<StandardInstrumentations> TheSI;
static std::map<std::string, std::unique_ptr<PrototypeAST>> FunctionProtos;
static ExitOnError ExitOnErr;
Value *LogErrorV(const char *Str) {
LogError(Str);
return nullptr;
}
Function *getFunction(std::string Name) {
// First, see if the function has already been added to the current module.
if (auto *F = TheModule->getFunction(Name))
return F;
// If not, check whether we can codegen the declaration from some existing
// prototype.
auto FI = FunctionProtos.find(Name);
if (FI != FunctionProtos.end())
return FI->second->codegen();
// If no existing prototype exists, return null.
return nullptr;
}
/// CreateEntryBlockAlloca - Create an alloca instruction in the entry block of
/// the function. This is used for mutable variables etc.
static AllocaInst *CreateEntryBlockAlloca(Function *TheFunction,
StringRef VarName) {
IRBuilder<> TmpB(&TheFunction->getEntryBlock(),
TheFunction->getEntryBlock().begin());
return TmpB.CreateAlloca(Type::getDoubleTy(*TheContext), nullptr, VarName);
}
Value *NumberExprAST::codegen() {
return ConstantFP::get(*TheContext, APFloat(Val));
}
Value *VariableExprAST::codegen() {
// Look this variable up in the function.
AllocaInst *A = NamedValues[Name];
if (!A)
return LogErrorV("Unknown variable name");
// Load the value.
return Builder->CreateLoad(A->getAllocatedType(), A, Name.c_str());
}
Value *UnaryExprAST::codegen() {
Value *OperandV = Operand->codegen();
if (!OperandV)
return nullptr;
Function *F = getFunction(std::string("unary") + Opcode);
if (!F)
return LogErrorV("Unknown unary operator");
return Builder->CreateCall(F, OperandV, "unop");
}
Value *BinaryExprAST::codegen() {
// Special case '=' because we don't want to emit the LHS as an expression.
if (Op == '=') {
// Assignment requires the LHS to be an identifier.
// This assume we're building without RTTI because LLVM builds that way by
// default. If you build LLVM with RTTI this can be changed to a
// dynamic_cast for automatic error checking.
VariableExprAST *LHSE = static_cast<VariableExprAST *>(LHS.get());
if (!LHSE)
return LogErrorV("destination of '=' must be a variable");
// Codegen the RHS.
Value *Val = RHS->codegen();
if (!Val)
return nullptr;
// Look up the name.
Value *Variable = NamedValues[LHSE->getName()];
if (!Variable)
return LogErrorV("Unknown variable name");
Builder->CreateStore(Val, Variable);
return Val;
}
Value *L = LHS->codegen();
Value *R = RHS->codegen();
if (!L || !R)
return nullptr;
switch (Op) {
case '+':
return Builder->CreateFAdd(L, R, "addtmp");
case '-':
return Builder->CreateFSub(L, R, "subtmp");
case '*':
return Builder->CreateFMul(L, R, "multmp");
case '<':
L = Builder->CreateFCmpULT(L, R, "cmptmp");
// Convert bool 0/1 to double 0.0 or 1.0
return Builder->CreateUIToFP(L, Type::getDoubleTy(*TheContext), "booltmp");
default:
break;
}
// If it wasn't a builtin binary operator, it must be a user defined one. Emit
// a call to it.
Function *F = getFunction(std::string("binary") + Op);
assert(F && "binary operator not found!");
Value *Ops[] = {L, R};
return Builder->CreateCall(F, Ops, "binop");
}
Value *CallExprAST::codegen() {
// Look up the name in the global module table.
Function *CalleeF = getFunction(Callee);
if (!CalleeF)
return LogErrorV("Unknown function referenced");
// If argument mismatch error.
if (CalleeF->arg_size() != Args.size())
return LogErrorV("Incorrect # arguments passed");
std::vector<Value *> ArgsV;
for (unsigned i = 0, e = Args.size(); i != e; ++i) {
ArgsV.push_back(Args[i]->codegen());
if (!ArgsV.back())
return nullptr;
}
return Builder->CreateCall(CalleeF, ArgsV, "calltmp");
}
Value *IfExprAST::codegen() {
Value *CondV = Cond->codegen();
if (!CondV)
return nullptr;
// Convert condition to a bool by comparing non-equal to 0.0.
CondV = Builder->CreateFCmpONE(
CondV, ConstantFP::get(*TheContext, APFloat(0.0)), "ifcond");
Function *TheFunction = Builder->GetInsertBlock()->getParent();
// Create blocks for the then and else cases. Insert the 'then' block at the
// end of the function.
BasicBlock *ThenBB = BasicBlock::Create(*TheContext, "then", TheFunction);
BasicBlock *ElseBB = BasicBlock::Create(*TheContext, "else");
BasicBlock *MergeBB = BasicBlock::Create(*TheContext, "ifcont");
Builder->CreateCondBr(CondV, ThenBB, ElseBB);
// Emit then value.
Builder->SetInsertPoint(ThenBB);
Value *ThenV = Then->codegen();
if (!ThenV)
return nullptr;
Builder->CreateBr(MergeBB);
// Codegen of 'Then' can change the current block, update ThenBB for the PHI.
ThenBB = Builder->GetInsertBlock();
// Emit else block.
TheFunction->insert(TheFunction->end(), ElseBB);
Builder->SetInsertPoint(ElseBB);
Value *ElseV = Else->codegen();
if (!ElseV)
return nullptr;
Builder->CreateBr(MergeBB);
// Codegen of 'Else' can change the current block, update ElseBB for the PHI.
ElseBB = Builder->GetInsertBlock();
// Emit merge block.
TheFunction->insert(TheFunction->end(), MergeBB);
Builder->SetInsertPoint(MergeBB);
PHINode *PN = Builder->CreatePHI(Type::getDoubleTy(*TheContext), 2, "iftmp");
PN->addIncoming(ThenV, ThenBB);
PN->addIncoming(ElseV, ElseBB);
return PN;
}
// Output for-loop as:
// var = alloca double
// ...
// start = startexpr
// store start -> var
// goto loop
// loop:
// ...
// bodyexpr
// ...
// loopend:
// step = stepexpr
// endcond = endexpr
//
// curvar = load var
// nextvar = curvar + step
// store nextvar -> var
// br endcond, loop, endloop
// outloop:
Value *ForExprAST::codegen() {
Function *TheFunction = Builder->GetInsertBlock()->getParent();
// Create an alloca for the variable in the entry block.
AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
// Emit the start code first, without 'variable' in scope.
Value *StartVal = Start->codegen();
if (!StartVal)
return nullptr;
// Store the value into the alloca.
Builder->CreateStore(StartVal, Alloca);
// Make the new basic block for the loop header, inserting after current
// block.
BasicBlock *LoopBB = BasicBlock::Create(*TheContext, "loop", TheFunction);
// Insert an explicit fall through from the current block to the LoopBB.
Builder->CreateBr(LoopBB);
// Start insertion in LoopBB.
Builder->SetInsertPoint(LoopBB);
// Within the loop, the variable is defined equal to the PHI node. If it
// shadows an existing variable, we have to restore it, so save it now.
AllocaInst *OldVal = NamedValues[VarName];
NamedValues[VarName] = Alloca;
// Emit the body of the loop. This, like any other expr, can change the
// current BB. Note that we ignore the value computed by the body, but don't
// allow an error.
if (!Body->codegen())
return nullptr;
// Emit the step value.
Value *StepVal = nullptr;
if (Step) {
StepVal = Step->codegen();
if (!StepVal)
return nullptr;
} else {
// If not specified, use 1.0.
StepVal = ConstantFP::get(*TheContext, APFloat(1.0));
}
// Compute the end condition.
Value *EndCond = End->codegen();
if (!EndCond)
return nullptr;
// Reload, increment, and restore the alloca. This handles the case where
// the body of the loop mutates the variable.
Value *CurVar =
Builder->CreateLoad(Alloca->getAllocatedType(), Alloca, VarName.c_str());
Value *NextVar = Builder->CreateFAdd(CurVar, StepVal, "nextvar");
Builder->CreateStore(NextVar, Alloca);
// Convert condition to a bool by comparing non-equal to 0.0.
EndCond = Builder->CreateFCmpONE(
EndCond, ConstantFP::get(*TheContext, APFloat(0.0)), "loopcond");
// Create the "after loop" block and insert it.
BasicBlock *AfterBB =
BasicBlock::Create(*TheContext, "afterloop", TheFunction);
// Insert the conditional branch into the end of LoopEndBB.
Builder->CreateCondBr(EndCond, LoopBB, AfterBB);
// Any new code will be inserted in AfterBB.
Builder->SetInsertPoint(AfterBB);
// Restore the unshadowed variable.
if (OldVal)
NamedValues[VarName] = OldVal;
else
NamedValues.erase(VarName);
// for expr always returns 0.0.
return Constant::getNullValue(Type::getDoubleTy(*TheContext));
}
Value *VarExprAST::codegen() {
std::vector<AllocaInst *> OldBindings;
Function *TheFunction = Builder->GetInsertBlock()->getParent();
// Register all variables and emit their initializer.
for (unsigned i = 0, e = VarNames.size(); i != e; ++i) {
const std::string &VarName = VarNames[i].first;
ExprAST *Init = VarNames[i].second.get();
// Emit the initializer before adding the variable to scope, this prevents
// the initializer from referencing the variable itself, and permits stuff
// like this:
// var a = 1 in
// var a = a in ... # refers to outer 'a'.
Value *InitVal;
if (Init) {
InitVal = Init->codegen();
if (!InitVal)
return nullptr;
} else { // If not specified, use 0.0.
InitVal = ConstantFP::get(*TheContext, APFloat(0.0));
}
AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, VarName);
Builder->CreateStore(InitVal, Alloca);
// Remember the old variable binding so that we can restore the binding when
// we unrecurse.
OldBindings.push_back(NamedValues[VarName]);
// Remember this binding.
NamedValues[VarName] = Alloca;
}
// Codegen the body, now that all vars are in scope.
Value *BodyVal = Body->codegen();
if (!BodyVal)
return nullptr;
// Pop all our variables from scope.
for (unsigned i = 0, e = VarNames.size(); i != e; ++i)
NamedValues[VarNames[i].first] = OldBindings[i];
// Return the body computation.
return BodyVal;
}
Function *PrototypeAST::codegen() {
// Make the function type: double(double,double) etc.
std::vector<Type *> Doubles(Args.size(), Type::getDoubleTy(*TheContext));
FunctionType *FT =
FunctionType::get(Type::getDoubleTy(*TheContext), Doubles, false);
Function *F =
Function::Create(FT, Function::ExternalLinkage, Name, TheModule.get());
// Set names for all arguments.
unsigned Idx = 0;
for (auto &Arg : F->args())
Arg.setName(Args[Idx++]);
return F;
}
Function *FunctionAST::codegen() {
// Transfer ownership of the prototype to the FunctionProtos map, but keep a
// reference to it for use below.
auto &P = *Proto;
FunctionProtos[Proto->getName()] = std::move(Proto);
Function *TheFunction = getFunction(P.getName());
if (!TheFunction)
return nullptr;
// If this is an operator, install it.
if (P.isBinaryOp())
BinopPrecedence[P.getOperatorName()] = P.getBinaryPrecedence();
// Create a new basic block to start insertion into.
BasicBlock *BB = BasicBlock::Create(*TheContext, "entry", TheFunction);
Builder->SetInsertPoint(BB);
// Record the function arguments in the NamedValues map.
NamedValues.clear();
for (auto &Arg : TheFunction->args()) {
// Create an alloca for this variable.
AllocaInst *Alloca = CreateEntryBlockAlloca(TheFunction, Arg.getName());
// Store the initial value into the alloca.
Builder->CreateStore(&Arg, Alloca);
// Add arguments to variable symbol table.
NamedValues[std::string(Arg.getName())] = Alloca;
}
if (Value *RetVal = Body->codegen()) {
// Finish off the function.
Builder->CreateRet(RetVal);
// Validate the generated code, checking for consistency.
verifyFunction(*TheFunction);
// Run the optimizer on the function.
TheFPM->run(*TheFunction, *TheFAM);
return TheFunction;
}
// Error reading body, remove function.
TheFunction->eraseFromParent();
if (P.isBinaryOp())
BinopPrecedence.erase(P.getOperatorName());
return nullptr;
}
//===----------------------------------------------------------------------===//
// Top-Level parsing and JIT Driver
//===----------------------------------------------------------------------===//
static void InitializeModuleAndManagers() {
// Open a new context and module.
TheContext = std::make_unique<LLVMContext>();
TheModule = std::make_unique<Module>("KaleidoscopeJIT", *TheContext);
TheModule->setDataLayout(TheJIT->getDataLayout());
// Create a new builder for the module.
Builder = std::make_unique<IRBuilder<>>(*TheContext);
// Create new pass and analysis managers.
TheFPM = std::make_unique<FunctionPassManager>();
TheLAM = std::make_unique<LoopAnalysisManager>();
TheFAM = std::make_unique<FunctionAnalysisManager>();
TheCGAM = std::make_unique<CGSCCAnalysisManager>();
TheMAM = std::make_unique<ModuleAnalysisManager>();
ThePIC = std::make_unique<PassInstrumentationCallbacks>();
TheSI = std::make_unique<StandardInstrumentations>(*TheContext,
/*DebugLogging*/ true);
TheSI->registerCallbacks(*ThePIC, TheMAM.get());
// Add transform passes.
// Do simple "peephole" optimizations and bit-twiddling optzns.
TheFPM->addPass(InstCombinePass());
// Reassociate expressions.
TheFPM->addPass(ReassociatePass());
// Eliminate Common SubExpressions.
TheFPM->addPass(GVNPass());
// Simplify the control flow graph (deleting unreachable blocks, etc).
TheFPM->addPass(SimplifyCFGPass());
// Register analysis passes used in these transform passes.
PassBuilder PB;
PB.registerModuleAnalyses(*TheMAM);
PB.registerFunctionAnalyses(*TheFAM);
PB.crossRegisterProxies(*TheLAM, *TheFAM, *TheCGAM, *TheMAM);
}
static void HandleDefinition() {
if (auto FnAST = ParseDefinition()) {
if (auto *FnIR = FnAST->codegen()) {
fprintf(stderr, "Read function definition:");
FnIR->print(errs());
fprintf(stderr, "\n");
ExitOnErr(TheJIT->addModule(
ThreadSafeModule(std::move(TheModule), std::move(TheContext))));
InitializeModuleAndManagers();
}
} else {
// Skip token for error recovery.
getNextToken();
}
}
static void HandleExtern() {
if (auto ProtoAST = ParseExtern()) {
if (auto *FnIR = ProtoAST->codegen()) {
fprintf(stderr, "Read extern: ");
FnIR->print(errs());
fprintf(stderr, "\n");
FunctionProtos[ProtoAST->getName()] = std::move(ProtoAST);
}
} else {
// Skip token for error recovery.
getNextToken();
}
}
static void HandleTopLevelExpression() {
// Evaluate a top-level expression into an anonymous function.
if (auto FnAST = ParseTopLevelExpr()) {
if (FnAST->codegen()) {
// Create a ResourceTracker to track JIT'd memory allocated to our
// anonymous expression -- that way we can free it after executing.
auto RT = TheJIT->getMainJITDylib().createResourceTracker();
auto TSM = ThreadSafeModule(std::move(TheModule), std::move(TheContext));
ExitOnErr(TheJIT->addModule(std::move(TSM), RT));
InitializeModuleAndManagers();
// Search the JIT for the __anon_expr symbol.
auto ExprSymbol = ExitOnErr(TheJIT->lookup("__anon_expr"));
// Get the symbol's address and cast it to the right type (takes no
// arguments, returns a double) so we can call it as a native function.
double (*FP)() = ExprSymbol.getAddress().toPtr<double (*)()>();
fprintf(stderr, "Evaluated to %f\n", FP());
// Delete the anonymous expression module from the JIT.
ExitOnErr(RT->remove());
}
} else {
// Skip token for error recovery.
getNextToken();
}
}
/// top ::= definition | external | expression | ';'
static void MainLoop() {
while (true) {
fprintf(stderr, "ready> ");
switch (CurTok) {
case tok_eof:
return;
case ';': // ignore top-level semicolons.
getNextToken();
break;
case tok_def:
HandleDefinition();
break;
case tok_extern:
HandleExtern();
break;
default:
HandleTopLevelExpression();
break;
}
}
}
//===----------------------------------------------------------------------===//
// "Library" functions that can be "extern'd" from user code.
//===----------------------------------------------------------------------===//
#ifdef _WIN32
#define DLLEXPORT __declspec(dllexport)
#else
#define DLLEXPORT
#endif
/// putchard - putchar that takes a double and returns 0.
extern "C" DLLEXPORT double putchard(double X) {
fputc((char)X, stderr);
return 0;
}
/// printd - printf that takes a double prints it as "%f\n", returning 0.
extern "C" DLLEXPORT double printd(double X) {
fprintf(stderr, "%f\n", X);
return 0;
}
//===----------------------------------------------------------------------===//
// Main driver code.
//===----------------------------------------------------------------------===//
int main() {
InitializeNativeTarget();
InitializeNativeTargetAsmPrinter();
InitializeNativeTargetAsmParser();
// Install standard binary operators.
// 1 is lowest precedence.
BinopPrecedence['='] = 2;
BinopPrecedence['<'] = 10;
BinopPrecedence['+'] = 20;
BinopPrecedence['-'] = 20;
BinopPrecedence['*'] = 40; // highest.
// Prime the first token.
fprintf(stderr, "ready> ");
getNextToken();
TheJIT = ExitOnErr(KaleidoscopeJIT::Create());
InitializeModuleAndManagers();
// Run the main "interpreter loop" now.
MainLoop();
return 0;
}