Clang常用命令

https://www.jianshu.com/p/96058bf1ecc2 https://blog.csdn.net/snsn1984/article/details/41077763

clang提供了一些命令,让我们可以对编译的过程进行一些配置和查看,下面我们就对一些常用的指令进行一个基本的介绍. 常用指令

All clang option official mannual¶

http://releases.llvm.org/7.0.1/tools/clang/docs/UsersManual.html#id39

查看编译的步骤¶

clang -ccc-print-phases main.m

输出结果

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0: input, “main.m”, objective-c
1: preprocessor, {0}, objective-c-cpp-output
2: compiler, {1}, ir
3: backend, {2}, assembler
4: assembler, {3}, object
5: linker, {4}, image
6: bind-arch, “x86_64”, {5}, image

查看编译结果 : clang -rewrite-objc main.m¶

查看操作内部命令，可以使用 -### 命令，只输出会运行哪些命令，不会真正执行。

Bash

clang -### main.m -o main


clang version 12.0.0 (https://github.com/llvm/llvm-project.git 154860af338f7b0c82cb04e91d6f199aa72cfdff)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/ken/workspace/llvm/build/bin
 "/home/ken/workspace/llvm/build/bin/clang-12" "-cc1" "-triple" "x86_64-unknown-linux-gnu" "-emit-obj" "-mrelax-all" "--mrelax-relocations" "-disable-free" "-main-file-name" "test.c" "-mrelocation-model" "static" "-mframe-pointer=all" "-fmath-errno" "-fno-rounding-math" "-mconstructor-aliases" "-munwind-tables" "-target-cpu" "x86-64" "-tune-cpu" "generic" "-fno-split-dwarf-inlining" "-debugger-tuning=gdb" "-resource-dir" "/home/ken/workspace/llvm/build/lib/clang/12.0.0" "-internal-isystem" "/usr/local/include" "-internal-isystem" "/home/ken/workspace/llvm/build/lib/clang/12.0.0/include" "-internal-externc-isystem" "/usr/include/x86_64-linux-gnu" "-internal-externc-isystem" "/include" "-internal-externc-isystem" "/usr/include" "-fdebug-compilation-dir" "/home/ken/test/int_compiler" "-ferror-limit" "19" "-fgnuc-version=4.2.1" "-fcolor-diagnostics" "-faddrsig" "-o" "/tmp/test-dd0586.o" "-x" "c" "test.c"
 "/usr/bin/ld" "-z" "relro" "--hash-style=gnu" "--eh-frame-hdr" "-m" "elf_x86_64" "-dynamic-linker" "/lib64/ld-linux-x86-64.so.2" "-o" "test" "/usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/crt1.o" "/usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/crti.o" "/usr/lib/gcc/x86_64-linux-gnu/9/crtbegin.o" "-L/usr/lib/gcc/x86_64-linux-gnu/9" "-L/usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu" "-L/usr/lib/gcc/x86_64-linux-gnu/9/../../../../lib64" "-L/lib/x86_64-linux-gnu" "-L/lib/../lib64" "-L/usr/lib/x86_64-linux-gnu" "-L/usr/lib/../lib64" "-L/usr/lib/x86_64-linux-gnu/../../lib64" "-L/usr/lib/gcc/x86_64-linux-gnu/9/../../.." "-L/home/ken/workspace/llvm/build/bin/../lib" "-L/lib" "-L/usr/lib" "/tmp/test-dd0586.o" "-lgcc" "--as-needed" "-lgcc_s" "--no-as-needed" "-lc" "-lgcc" "--as-needed" "-lgcc_s" "--no-as-needed" "/usr/lib/gcc/x86_64-linux-gnu/9/crtend.o" "/usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/crtn.o"

想看清clang的全部过程，可以先通过-E查看clang在预编译处理这步做了什么。宏展开

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clang -E -o test.e test.c
宏定义会被去掉，不再依赖于相对位置的头文件。

clang基本语法介绍¶

针对下面会用到的语法进行分析

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    -fmodules
    允许modules的语言特性

    -fsyntax-only
    防止编译器生成代码,只是语法级别的说明和修改

    -Xclang <arg>
    向clang编译器传递参数

    -dump-tokens
    运行预处理器,拆分内部代码段为各种token

    -ast-dump
    构建抽象语法树AST,然后对其进行拆解和调试

    -S
    只运行预处理和编译步骤

    -fobjc-arc
    为OC对象生成retain和release的调用

    -emit-llvm
    使用LLVM描述汇编和对象文件

    -o <file>
    输出到目标文件

    -mllvm llvm-opt
     后面的选项是给llc使用的如： -mllvm -debug

    -c
    只运行预处理,编译和汇编步骤

    ## -mllvm -debug
Enable debug output
`-mllvm`: Additional arguments to forward to LLVM's option processing

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clang -O3 -mllvm -debug test.c -S -emit-llvm > debug.log 2>&1
llc clang_O3.ll -debug > llc.log 2>&1
clang 17.c -c  -mllvm -debug > 17.log 2>&1

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    -v
    编译，并输出编译时所使用的命令行

其余的就不多赘述了, 查看更多的clang使用方法可以在终端输入clang --hep查看,也可以点击如下链接: clang options

clang -O3 -emit-llvm -S¶

clang将调用opt做机器无关优化 opt只会做机器无关优化

clang --cc1¶

The Clang compiler front-end has several additional Clang specific features which are not exposed through the GCC compatibility driver interface. The -cc1 argument indicates that the compiler front-end is to be used, and not the driver. The clang -cc1 functionality implements the core compiler functionality. So, simply speaking. If you do not give -cc1 then you can expect the "look&feel" of standard GCC. That is the vast majority of compiler flags work just like you would expect them to work with GCC. If you pass the option "-cc1" then you get the Clang compiler flag set. Thus, there might be differences to GCC.

If you use cc1, you should not use -S, -cc1 -S will give you the machine assembly.

clang is the driver compatible with GCC. And the clang -cc1 is core compiler functionality. When you use clang to build program, it will call clang -cc1, you can use -v option to check the real command.

Notice clang -cc1 -emit-llvm is different with clang -S -emit-llvm.

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/home/ken/llvm/build/bin/clang -cc1 -internal-isystem /home/ken/llvm/build/lib/clang/8.0.0/include -nostdsysteminc -target-feature +altivec -target-feature +htm -triple powerpc64-unknown-unknown -emit-llvm /home/ken/llvm/clang/test/CodeGen/builtins-ppc-htm.c -o -

Bash

clang -S -emit-llvm test.c -o test.ll
is equal to
clang -cc1 -emit-llvm test.c -o test.ll

Get the assembly form the source code¶

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clang -S add.c -o clang.s -O3

NOTICE¶

If you use the clang with O0 or none opt option, it will add optnone in the function arrtibutes, so you will can't to use the opt to optimize the ll file. You should do it like this, it will remove the optnone attribute and noinline.

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clang -O1 -mllvm -disable-llvm-optzns -mllvm -disable-llvm-passes sum.c -S -emit-llvm

-mllvm¶

后面根传给llc的选项，如-mllvm -debug。

### -mllvm —stats

输出l,./ 统计信息

Note that in order to use the ‘-stats’ option, LLVM must be compiled with assertions enabled.