生成LLVM IR及其CFG图

math.c代码

int add(int a, int b)
{
    return a+b;
}

int mul(int a, int b)
{
    return a*b;
}

void Test()
{
    int r1 = add(1,2);
    int r2 = mul(3,4);
}

编译生成IR中间代码math.ll

clang.exe -S -emit-llvm math.c -o math.ll

math.ll代码如下：

; ModuleID = 'math.c'
source_filename = "math.c"
target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-pc-windows-msvc19.29.30152"

; Function Attrs: noinline nounwind optnone uwtable
define dso_local i32 @add(i32, i32) #0 {
  %3 = alloca i32, align 4
  %4 = alloca i32, align 4
  store i32 %1, i32* %3, align 4
  store i32 %0, i32* %4, align 4
  %5 = load i32, i32* %4, align 4
  %6 = load i32, i32* %3, align 4
  %7 = add nsw i32 %5, %6
  ret i32 %7
}

; Function Attrs: noinline nounwind optnone uwtable
define dso_local i32 @mul(i32, i32) #0 {
  %3 = alloca i32, align 4
  %4 = alloca i32, align 4
  store i32 %1, i32* %3, align 4
  store i32 %0, i32* %4, align 4
  %5 = load i32, i32* %4, align 4
  %6 = load i32, i32* %3, align 4
  %7 = mul nsw i32 %5, %6
  ret i32 %7
}

; Function Attrs: noinline nounwind optnone uwtable
define dso_local void @Test() #0 {
  %1 = alloca i32, align 4
  %2 = alloca i32, align 4
  %3 = call i32 @add(i32 1, i32 2)
  store i32 %3, i32* %1, align 4
  %4 = call i32 @mul(i32 3, i32 4)
  store i32 %4, i32* %2, align 4
  ret void
}

attributes #0 = { noinline nounwind optnone uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "min-legal-vector-width"="0" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }

!llvm.module.flags = !{!0, !1}
!llvm.ident = !{!2}

!0 = !{i32 1, !"wchar_size", i32 2}
!1 = !{i32 7, !"PIC Level", i32 2}
!2 = !{!"clang version 9.0.1 (https://github.com/llvm-project.git 4dc5e59b6369d07ec453a3da46cf7fb51ce487ba)"}

生成函数调用关系CFG图

opt.exe -dot-callgraph math.ll

注1：CFG（control-flow graph）即控制流图

注2：上述命令会生成callgraph.dot的CFG文件

callgraph.dot文件内容如下：

digraph "Call graph" {
    label="Call graph";

    Node0x2abc6af0cb0 [shape=record,label="{external node}"];
    Node0x2abc6af0cb0 -> Node0x2abc6af1220;
    Node0x2abc6af0cb0 -> Node0x2abc6af1430;
    Node0x2abc6af0cb0 -> Node0x2abc6af0f50;
    Node0x2abc6af1220 [shape=record,label="{add}"];
    Node0x2abc6af1430 [shape=record,label="{mul}"];
    Node0x2abc6af0f50 [shape=record,label="{Test}"];
    Node0x2abc6af0f50 -> Node0x2abc6af1220;
    Node0x2abc6af0f50 -> Node0x2abc6af1430;
}

Graphviz Interactive预览如下：

生成函数CFG图

opt.exe -dot-cfg math.ll

注：会为math.ll中每个函数都生成一个.dot文件（形如.函数名.dot）

.add.dot代码如下：

digraph "CFG for 'add' function" {
    label="CFG for 'add' function";

    Node0x1f698b61d50 [shape=record,label="{%2:\l  %3 = alloca i32, align 4\l  %4 = alloca i32, align 4\l  store i32 %1, i32* %3, align 4\l  store i32 %0, i32* %4, align 4\l  %5 = load i32, i32* %4, align 4\l  %6 = load i32, i32* %3, align 4\l  %7 = add nsw i32 %5, %6\l  ret i32 %7\l}"];
}

Graphviz Interactive预览如下：

.mul.dot代码如下：

digraph "CFG for 'mul' function" {
    label="CFG for 'mul' function";

    Node0x1f698b62230 [shape=record,label="{%2:\l  %3 = alloca i32, align 4\l  %4 = alloca i32, align 4\l  store i32 %1, i32* %3, align 4\l  store i32 %0, i32* %4, align 4\l  %5 = load i32, i32* %4, align 4\l  %6 = load i32, i32* %3, align 4\l  %7 = mul nsw i32 %5, %6\l  ret i32 %7\l}"];
}

Graphviz Interactive预览如下：

.Test.dot代码如下：

digraph "CFG for 'Test' function" {
    label="CFG for 'Test' function";

    Node0x1f698b624d0 [shape=record,label="{%0:\l  %1 = alloca i32, align 4\l  %2 = alloca i32, align 4\l  %3 = call i32 @add(i32 1, i32 2)\l  store i32 %3, i32* %1, align 4\l  %4 = call i32 @mul(i32 3, i32 4)\l  store i32 %4, i32* %2, align 4\l  ret void\l}"];
}

Graphviz Interactive预览如下：