-emit-llvm in Linux

问题:

I am a newbie to LLVM and try to generate a human readable .ll file on Linux. I installed llvm-gcc but as I see it can generate only assembly code (-S option). Is there any way to get something like what is generated by llvm online compiler?

That's what I get with -S -emit-llvm on Linux:

    .file   "hello.c"      .ident  "GCC: (Ubuntu/Linaro 4.5.1-7ubuntu2) 4.5.1 LLVM: "      .text     .globl  main     .align  16, 0x90     .type   main,@function main:     pushl   %ebp     movl    %esp, %ebp     subl    $8, %esp     movl    $.L.str, 4(%esp)     movl    $1, (%esp)     call    __printf_chk     xorl    %eax, %eax     addl    $8, %esp     popl    %ebp     ret .Ltmp0:     .size   main, .Ltmp0-main      .type   .L.str,@object     .section    .rodata.str1.1,"aMS",@progbits,1 .L.str:     .asciz   "hello world\n"     .size   .L.str, 13      .section    .note.GNU-stack,"",@progbits 

That's what I am trying to get:

; ModuleID = '/tmp/webcompile/_7829_0.bc' target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64" target triple = "x86_64-linux-gnu"  @.str = private constant [12 x i8] c"hello world\00", align 1 ; <[12 x i8]*> [#uses=1]  define i32 @main() nounwind { entry:   %0 = tail call i32 @puts(i8* getelementptr inbounds ([12 x i8]* @.str, i64 0, i64 0)) nounwind ; <i32> [#uses=0]   ret i32 0 }  declare i32 @puts(i8* nocapture) nounwind 

On windows I successfully get this file with the same command: llvm-gcc -S -emit-llvm hello.c.

回答1:

Something is horrible broken in ubuntu packaging of llvm-gcc. llvm-gcc's version is 4.2.1, but here we're seeing 4.5. Please report Ubuntu bug.

回答2:

Try:

llvm-gcc -c -emit-llvm source.cpp 

use -c instead of -S.

if it does not work, use:

clang -c -emit-llvm source.cpp 

You can build llvm either from Ubuntu software center or download llvm-3.0-src and clang-src to compile them yourself.

回答3:

From the LLVM tutorial:

$ llvm-gcc -O3 -emit-llvm hello.c -c -o hello.bc 

Will compile the source hello.c into bytecode file hello.bc.

Then use the llvm-dis utility to take a look at the LLVM assembly code:

$ llvm-dis < hello.bc | less 

回答4:

If you want to play with LLVM, build it from source: http://clang.llvm.org/get_started.html

Otherwise, to quick start, try to install clang on Ubuntu. This is the C/C++ compiler built on top of LLVM. You will be able to generate LLVM IR from clang directly.

llvm-gcc seems to be based on dragon-egg, which is no longer supported in LLVM AFAIK.

回答5:

Do the steps on http://clang.llvm.org/get_started.html this will install llvm and clang from svn. So you'll build from source

but with minor difference: ../llvm/configure --prefix=/usr/local --enable-optimized make -j4 make install (to install tools under /usr/local)

(install release+asserts instead of debug+asserts or go with ../llvm/configure for debug+asserts I have an i5 so I used make -j4 change as you wish)

use clang not llvm-gcc. You can then directly generate an .ll by: clang -S -emit-llvm file.cpp -o file.ll

and clang -c -emit-llvm file.cpp -o file.bc

if you like to get and .s do the following: llc file.bc

this is the cleanest way for the latest version of llvm on ubuntu

---

Same thing happens with llvm-gcc-4.6 which is also dragonEgg version I suppose.

I'm getting llvm-gcc potential incompatible plug-in version

After this point I get exactly the same error with llvm-dis:

"llvm-dis: Invalid bitcode signature".

文章来源: -emit-llvm in Linux