[LLVMdev] Problem while compling SPEC2000 with llvm-gcc

[Li Shengmei]

Thanks a lot, Edwim
	About the performance of comparison between gcc and llvm-gcc, I use llvm-gcc -O3 directly to compile SPEC2000. I think it's not necessary to do the steps as follows:
llvm-gcc -emit-llvm hello.c -c -o hello.bc
llc hello.bc -o hell.s
gcc hello.s -o hello
./hello

Right?

Because on the website "http://llvm.org/docs/GettingStarted.html"  There is a sentence "Note that using llvm-gcc to compile directly to native code (i.e. when the -emit-llvm option is not present) does steps 6/7/8 for you."

The results are as follows. The number is the time(s). You can see many benchmarks run more slowly with llvm-gcc -O3 than gcc -O3. I hope we can have further discussion. Thanks.

	GCC -O3	llvm-gcc O3
164.gzip	109	106
175.vpr	146	165
176.gcc	95.1	99.3
181.mcf	391	395
186.crafty	72.1	96.7
197.parser	191	200
252.eon		
253.perlbmk	171	261
254.gap	172	198
255.vortex	206	226
256.bzip2	142	154
300.twolf	271	272


Shengmei


----------
发件人: Török Edwin [mailto:edwintorok at gmail.com] 
发送时间: 2009年12月23日 22:01
收件人: Li Shengmei
抄送: llvmdev at cs.uiuc.edu
主题: Re: [LLVMdev] Problem while compling SPEC2000 with llvm-gcc

On 2009-12-23 08:22, Li Shengmei wrote:
>
> Hi, all
>
>          I use llvm-gcc –O4 to compile SPEC 2000, some benchmarks
> can’t be built successfully, such as 164.gzip, 175.vpr etc.
>
> The error messages are as follows.
>
>  
>
> ……
>
> zh.o unlzw.o unpack.o unzip.o util.o zip.o     -o gzip
>
> bits.o: file not recognized: File format not recognized
>

-O4 outputs LLVM bitcode, instead of ELF files, thus requires a linker
that is able to understand it (such as the Gold linker, with the LLVM
plugin).
Try compiling any C source file with -O4, it won't work unless you have
special support from the linker.

> collect2: ld returned 1 exit status
>
> specmake: *** [gzip] Error 1
>
> specmake  options 2> options.err | tee options.out
>
> COMP: /home2/lishengmei/tools/llvm-gcc-4.2/bin/llvm-gcc  -c -o
> options.o    -O4
>
> LINK: /home2/lishengmei/tools/llvm-gcc-4.2/bin/llvm-gcc              
> -o options
>
>   Some files did not appear to be built: gzip
>
> *** Error building 164.gzip
>
> If you wish to ignore this error, please use '-I' or ignore errors.
>
>  
>
> When I use O3 instead of O4, the errors disappear. I use llvm-2.6
> version on Red hat Linux. The CPU is “Dual-Core AMD Opteron(tm)
> Processor 8218”
>
> Can anyone give help?
>

This page describes how to build Gold, and LLVM's plugin:
http://llvm.org/docs/GoldPlugin.html


>  
>
> Btw, some benchmarks run more slowly wth llvm-gcc O3 than with gcc
> O3(version is 4.4.2) on my system. Such as 186.crafty, 253.perlbmk,
> 254.gap
>
> Anyone give comments?
>

How much slower?

Best regards,
--Edwin