我对LLVM和编译器有些不熟悉。
我决定使用以下命令生成一个DAG
llc -view-sched-dags hello_world.ll
我有一个非常大的图，其中包含不同类型的依赖关系。《LLVM核心库入门》一书解释说：
黑色箭头表示数据流依赖
红色箭头表示粘合依赖
蓝色虚线箭头表示链式依赖
我清楚地记得在学校的编译器课程中讨论过数据流依赖。但我不记得讨论过其他两个依赖关系。有人可以解释一下其他依赖关系的含义吗？感谢任何帮助。
hello_world.cpp
#include <stdio.h>
#include <assert.h>
int sum(int a, int b) {
return a + b;
}
int main(int argc, char** argv) {
printf("Hello World! %d\n", sum(argc, 1));
return 0;
}
你好_世界.ll
; ModuleID = 'hello_world.cpp'
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
@.str = private unnamed_addr constant [17 x i8] c"Hello World! %d\0A\00", align 1
; Function Attrs: nounwind uwtable
define i32 @_Z3sumii(i32 %a, i32 %b) #0 {
entry:
%a.addr = alloca i32, align 4
%b.addr = alloca i32, align 4
store i32 %a, i32* %a.addr, align 4
store i32 %b, i32* %b.addr, align 4
%0 = load i32* %a.addr, align 4
%1 = load i32* %b.addr, align 4
%add = add nsw i32 %0, %1
ret i32 %add
}
; Function Attrs: uwtable
define i32 @main(i32 %argc, i8** %argv) #1 {
entry:
%retval = alloca i32, align 4
%argc.addr = alloca i32, align 4
%argv.addr = alloca i8**, align 8
store i32 0, i32* %retval
store i32 %argc, i32* %argc.addr, align 4
store i8** %argv, i8*** %argv.addr, align 8
%0 = load i32* %argc.addr, align 4
%call = call i32 @_Z3sumii(i32 %0, i32 1)
%call1 = call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([17 x i8]* @.str, i32 0, i32 0), i32 %call)
ret i32 0
}
declare i32 @printf(i8*, ...) #2
attributes #0 = { nounwind uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #1 = { uwtable "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
attributes #2 = { "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "unsafe-fp-math"="false" "use-soft-float"="false" }
!llvm.ident = !{!0}
!0 = metadata !{metadata !"clang version 3.5.0 "}
你好_世界.主图.jpg
你好_世界.汇总图.jpg
