7. 萬花筒：擴展語言：可變變數¶
7.1. 第 7 章 導言¶
歡迎來到“使用 LLVM 實作語言”教學的第 7 章。在第 1 章到第 6 章中，我們建構了一個非常值得尊敬，雖然簡單的 函數式程式語言。在我們的旅程中，我們學習了一些解析技術、如何建構和表示 AST、如何建構 LLVM IR，以及如何最佳化結果程式碼以及 JIT 編譯它。
雖然萬花筒作為一種函數式語言很有趣，但它實際上是函數式的這一事實使得為其產生 LLVM IR 變得“太容易”。特別是，函數式語言使得直接以 SSA 形式建構 LLVM IR 非常容易。由於 LLVM 要求輸入程式碼為 SSA 形式，這是一個非常好的特性，而且對於新手來說，如何為具有可變變數的命令式語言產生程式碼通常是不清楚的。
本章的簡短（且令人高興的）總結是，你的前端不需要建構 SSA 形式：LLVM 為此提供了高度調整和充分測試的支援，儘管它的工作方式對某些人來說有點出乎意料。
7.2. 為什麼這是個難題？¶
為了理解為什麼可變變數會在 SSA 建構中引起複雜性，請考慮這個非常簡單的 C 範例
int G, H;
int test(_Bool Condition) {
int X;
if (Condition)
X = G;
else
X = H;
return X;
}
在這種情況下，我們有一個變數“X”，其值取決於程式中執行的路徑。因為在 return 指令之前，X 有兩個不同的可能值，所以插入一個 PHI 節點來合併這兩個值。我們希望這個範例的 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
}
在這個範例中，從 G 和 H 全域變數的載入在 LLVM IR 中是顯式的，它們存在於 if 語句的 then/else 分支（cond_true/cond_false）中。為了合併傳入的值，cond_next 區塊中的 X.2 phi 節點根據控制流程的來源選擇要使用的正確值：如果控制流程來自 cond_false 區塊，則 X.2 取得 X.1 的值。或者，如果控制流程來自 cond_true，則它取得 X.0 的值。本章的目的不是解釋 SSA 形式的細節。有關更多資訊，請參閱眾多 線上參考資料之一。
本文的問題是“當將賦值降低為可變變數時，誰放置 phi 節點？”。這裡的問題是 LLVM 要求其 IR 為 SSA 形式：沒有“非 SSA”模式。然而，SSA 建構需要非平凡的演算法和資料結構，因此對於每個前端來說，都必須重現這種邏輯是不方便且浪費的。
7.3. LLVM 中的記憶體¶
這裡的“訣竅”是，雖然 LLVM 確實要求所有暫存器值都採用 SSA 形式，但它不要求（或允許）記憶體物件採用 SSA 形式。在上面的範例中，請注意從 G 和 H 的載入是對 G 和 H 的直接存取：它們沒有被重新命名或版本化。這與其他一些編譯器系統不同，後者確實嘗試對記憶體物件進行版本化。在 LLVM 中，不是將記憶體的資料流分析編碼到 LLVM IR 中，而是使用 分析Pass 處理，這些Pass是根據需要計算的。
考慮到這一點，高階想法是我們想要為函數中的每個可變物件建立一個堆疊變數（它存在於記憶體中，因為它在堆疊上）。為了利用這個訣竅，我們需要討論 LLVM 如何表示堆疊變數。
在 LLVM 中，所有記憶體存取都使用 load/store 指令顯式表示，並且經過仔細設計，不具有（或需要）“address-of”運算子。請注意，即使變數定義為“i32”，@G/@H 全域變數的類型實際上是“i32*”。這表示 @G 在全域資料區域中為 i32 定義了空間，但它的名稱實際上是指該空間的位址。堆疊變數的工作方式相同，只是它們不是使用全域變數定義宣告的，而是使用 LLVM alloca 指令宣告的
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
...
此程式碼顯示了如何在 LLVM IR 中宣告和操作堆疊變數的範例。使用 alloca 指令配置的堆疊記憶體是完全通用的：你可以將堆疊槽的位址傳遞給函數，你可以將其儲存在其他變數中等等。在我們上面的範例中，我們可以重寫該範例以使用 alloca 技術來避免使用 PHI 節點
@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
}
有了這個，我們發現了一種處理任意可變變數的方法，而無需建立任何 Phi 節點
每個可變變數都變成堆疊配置。
每次讀取變數都會變成從堆疊載入。
每次更新變數都會變成儲存到堆疊。
取得變數的位址只是直接使用堆疊位址。
雖然這個解決方案解決了我們眼前的問題，但它引入了另一個問題：我們現在顯然為非常簡單和常見的操作引入了大量的堆疊流量，這是一個主要的效能問題。幸運的是，LLVM 最佳化器有一個高度調整的最佳化Pass，名為“mem2reg”，可以處理這種情況，將這樣的 allocas 提升到 SSA 暫存器中，並在適當的時候插入 Phi 節點。例如，如果你透過 Pass 執行這個範例，你會得到
$ 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 pass 實作了用於建構 SSA 形式的標準“迭代支配邊界”演算法，並且有許多最佳化可以加速（非常常見的）退化情況。mem2reg 最佳化Pass是處理可變變數的答案，我們強烈建議你依賴它。請注意，mem2reg 僅在某些情況下適用於變數
mem2reg 是 alloca 驅動的：它尋找 allocas，如果它可以處理它們，它會提升它們。它不適用於全域變數或堆積配置。
mem2reg 僅在函數的進入區塊中尋找 alloca 指令。位於進入區塊中可確保 alloca 僅執行一次，這使得分析更簡單。
mem2reg 僅提升其用途是直接載入和儲存的 allocas。如果堆疊物件的位址傳遞給函數，或者如果涉及任何有趣的指標運算，則不會提升 alloca。
mem2reg 僅適用於 first class 值（例如指標、純量和向量）的 allocas，並且僅當配置的陣列大小為 1（或在 .ll 檔案中遺失）時。mem2reg 無法將結構或陣列提升到暫存器。請注意，“sroa”pass 更強大，可以在許多情況下提升結構、“聯合”和陣列。
對於大多數命令式語言來說，所有這些屬性都很容易滿足，我們將在下面使用萬花筒來說明這一點。你可能要問的最後一個問題是：我應該為我的前端費心處理這種無稽之談嗎？如果我直接進行 SSA 建構，避免使用 mem2reg 最佳化Pass，豈不是更好嗎？簡而言之，我們強烈建議你使用這種技術來建構 SSA 形式，除非有極好的理由不這樣做。使用這種技術是
經過驗證和充分測試：clang 對於區域可變變數使用這種技術。因此，LLVM 最常見的客戶端正在使用它來處理大量變數。你可以確信錯誤會被快速發現並儘早修復。
極快：mem2reg 有許多特殊情況，使其在常見情況下以及完全通用的情況下都很快。例如，它對於僅在單個區塊中使用的變數、僅具有一個賦值點的變數具有快速路徑，以及避免插入不必要的 phi 節點的良好啟發式方法等等。
除錯資訊產生所需：LLVM 中的除錯資訊依賴於公開變數的位址，以便可以將除錯資訊附加到它。這種技術與這種風格的除錯資訊非常自然地吻合。
如果沒有別的，這使得你的前端更容易啟動和運行，並且非常容易實作。現在讓我們用可變變數擴展萬花筒！
7.4. 萬花筒中的可變變數¶
現在我們知道要解決的問題類型，讓我們看看這在我們的小萬花筒語言的上下文中是什麼樣子的。我們將新增兩個功能
使用“=”運算子變更變數的能力。
定義新變數的能力。
雖然第一項才是我們真正要討論的內容，但我們只有用於傳入引數以及歸納變數的變數，而重新定義這些變數的作用有限 :)。此外，無論你是否要變更它們，定義新變數的能力都是一件有用的事情。這是一個動機範例，展示了我們如何使用這些
# 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);
為了變更變數，我們必須變更現有變數以使用“alloca 訣竅”。一旦我們有了這個，我們將新增我們的新運算子，然後擴展萬花筒以支援新的變數定義。
7.5. 調整現有變數以進行變更¶
萬花筒中的符號表在程式碼產生時由“NamedValues”映射管理。此映射目前追蹤 LLVM “Value*”，它保存命名變數的 double 值。為了支援變更，我們需要稍微更改一下，以便 NamedValues 保存所討論變數的記憶體位置。請注意，此變更是重構：它更改了程式碼的結構，但（本身）不會更改編譯器的行為。所有這些更改都隔離在萬花筒程式碼產生器中。
在萬花筒開發的這一點上，它僅支援兩種變數：函數的傳入引數和“for”迴圈的歸納變數。為了保持一致性，除了其他使用者定義的變數之外，我們還將允許變更這些變數。這表示這些都需要記憶體位置。
為了開始我們對萬花筒的轉換，我們將更改 NamedValues 映射，使其映射到 AllocaInst* 而不是 Value*。一旦我們這樣做，C++ 編譯器將告訴我們需要更新程式碼的哪些部分
static std::map<std::string, AllocaInst*> NamedValues;
此外，由於我們需要建立這些 allocas，我們將使用一個輔助函數，以確保在函數的進入區塊中建立 allocas
/// 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);
}
這個看起來很有趣的程式碼建立了一個 IRBuilder 物件，它指向進入區塊的第一個指令 (.begin())。然後，它使用預期的名稱建立一個 alloca 並傳回它。由於萬花筒中的所有值都是 doubles，因此無需傳入要使用的類型。
有了這個，我們想要做的第一個功能變更是變數參考。在我們的新方案中，變數存在於堆疊上，因此產生對它們的參考的程式碼實際上需要從堆疊槽產生載入
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());
}
如你所見，這非常簡單明瞭。現在我們需要更新定義變數的事物以設定 alloca。我們將從 ForExprAST::codegen() 開始（有關未刪節的程式碼，請參閱完整程式碼列表）
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);
...
此程式碼與在我們允許可變變數之前的程式碼幾乎相同。最大的不同是我們不再需要建構 PHI 節點，並且我們根據需要使用 load/store 來存取變數。
為了支援可變引數變數，我們還需要為它們建立 allocas。此程式碼也很簡單
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()) {
...
對於每個引數，我們建立一個 alloca，將函數的輸入值儲存到 alloca 中，並將 alloca 註冊為引數的記憶體位置。此方法在 FunctionAST::codegen() 設定函數的進入區塊後立即調用。
最後缺少的環節是新增 mem2reg pass，這使我們能夠再次獲得良好的程式碼產生
// Promote allocas to registers.
TheFPM->addPass(PromotePass());
// Do simple "peephole" optimizations and bit-twiddling optzns.
TheFPM->addPass(InstCombinePass());
// Reassociate expressions.
TheFPM->addPass(ReassociatePass());
...
有趣的是看看程式碼在 mem2reg 最佳化運行之前和之後的樣子。例如，這是我們的遞迴 fib 函數的最佳化前後程式碼。最佳化前
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
}
這裡只有一個變數（x，輸入引數），但你仍然可以看到我們正在使用的極其簡單的程式碼產生策略。在進入區塊中，建立一個 alloca，並將初始輸入值儲存到其中。每次參考變數都會從堆疊重新載入。另外，請注意我們沒有修改 if/then/else 表達式，因此它仍然插入一個 PHI 節點。雖然我們可以為其建立一個 alloca，但實際上為其建立一個 PHI 節點更容易，因此我們仍然只建立 PHI。
這是 mem2reg pass 運行後的程式碼
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
}
對於 mem2reg 來說，這是一個微不足道的情況，因為沒有變數的重新定義。展示這一點的目的是讓你放鬆對插入如此公然的低效率的緊張感 :)。
在其他最佳化器運行後，我們得到
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
}
在這裡我們看到 simplifycfg pass 決定將 return 指令複製到“else”區塊的末尾。這使其能夠消除一些分支和 PHI 節點。
現在所有符號表參考都已更新為使用堆疊變數，我們將新增賦值運算子。
7.6. 新的賦值運算子¶
使用我們目前的框架，新增一個新的賦值運算子非常簡單。我們將像解析任何其他二元運算子一樣解析它，但在內部處理它（而不是允許使用者定義它）。第一步是設定優先順序
int main() {
// Install standard binary operators.
// 1 is lowest precedence.
BinopPrecedence['='] = 2;
BinopPrecedence['<'] = 10;
BinopPrecedence['+'] = 20;
BinopPrecedence['-'] = 20;
現在解析器知道二元運算子的優先順序，它負責所有解析和 AST 產生。我們只需要為賦值運算子實作程式碼產生。這看起來像
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");
與其他二元運算子不同，我們的賦值運算子不遵循“emit LHS, emit RHS, do computation”模型。因此，它在處理其他二元運算子之前作為特殊情況處理。另一個奇怪的事情是它要求 LHS 是一個變數。擁有“(x+1) = expr”是無效的 - 只允許像“x = expr”這樣的東西。
// 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;
}
...
一旦我們有了變數，賦值的程式碼產生就很簡單：我們產生賦值的 RHS，建立一個儲存，並傳回計算出的值。傳回值允許鏈式賦值，例如“X = (Y = Z)”。
現在我們有了一個賦值運算子，我們可以變更迴圈變數和引數。例如，我們現在可以運行像這樣的程式碼
# 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);
運行時，這個範例列印“123”，然後列印“4”，表明我們確實變更了值！好的，我們現在已經正式實作了我們的目標：在一般情況下，要使其工作需要 SSA 建構。但是，為了真正有用，我們希望能夠定義自己的區域變數，讓我們接下來新增這個！
7.7. 使用者定義的區域變數¶
新增 var/in 就像我們對萬花筒進行的任何其他擴展一樣：我們擴展詞法分析器、解析器、AST 和程式碼產生器。新增我們新的“var/in”結構的第一步是擴展詞法分析器。與之前一樣，這非常簡單，程式碼如下所示
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;
...
下一步是定義我們將建構的 AST 節點。對於 var/in，它看起來像這樣
/// 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 允許一次定義名稱列表，並且每個名稱可以選擇性地具有初始值。因此，我們在 VarNames 向量中捕獲此資訊。此外，var/in 有一個主體，該主體被允許存取由 var/in 定義的變數。
有了這個，我們可以定義解析器片段。我們做的第一件事是將其新增為主要表達式
/// 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();
}
}
接下來我們定義 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");
此程式碼的第一部分將識別碼/expr 對列表解析為本機 VarNames 向量。
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");
}
一旦解析了所有變數，我們然後解析主體並建立 AST 節點
// 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));
}
現在我們可以解析和表示程式碼，我們需要支援為其發射 LLVM IR。此程式碼從以下內容開始
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，它循環遍歷所有變數，一次安裝一個變數。對於我們放入符號表的每個變數，我們都會記住我們在 OldBindings 中替換的先前值。
// 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;
}
這裡的註解比程式碼還多。基本思想是我們產生初始值設定項，建立 alloca，然後更新符號表以指向它。一旦所有變數都安裝在符號表中，我們就評估 var/in 表達式的主體
// Codegen the body, now that all vars are in scope.
Value *BodyVal = Body->codegen();
if (!BodyVal)
return nullptr;
最後，在傳回之前，我們恢復先前的變數綁定
// 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;
}
所有這些的最終結果是我們獲得了正確範圍的變數定義，甚至（微不足道地）允許變更它們 :)。
有了這個，我們完成了我們著手要做的事情。我們從簡介中得到的漂亮迭代 fib 範例可以正常編譯和運行。mem2reg pass 將我們所有的堆疊變數最佳化到 SSA 暫存器中，在需要時插入 PHI 節點，並且我們的前端仍然很簡單：任何地方都看不到“迭代支配邊界”計算。
7.8. 完整程式碼列表¶
這是我們正在運行的範例的完整程式碼列表，其中增強了可變變數和 var/in 支援。要建構此範例，請使用
# Compile
clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core orcjit native` -O3 -o toy
# Run
./toy
這是程式碼
#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/Mem2Reg.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.
// Promote allocas to registers.
TheFPM->addPass(PromotePass());
// 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.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;
}