does clang and llvm take more time to compile c code

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#1

Hello, all

When I compile mpeg2enc of Mediabench, it seems clang and llvm take longer time than gcc. I meausre the time as follow:

gcc -O3 8.190sclang -O3 20.253s

will this means clang and llvm are slower than gcc in compiling c code.

Eric

#2

Possibly. The timings are useless without information about the versions of GCC and clang used and the build configuration (clang is extremely slow when built without optimization).

- Ben

#3

Hi, Ben
gcc version is: 4.7.0
clang version is: 3.2

The command options are:

  1. clang
    generated object files: clang -O3 -c *.c -o x.o
    link: clang *.o -lm -o mpeg2enc

  2. gcc

generated object files: gcc -O3 -c *.c -o x.o
link: gcc *.o -lm -o mpeg2enc

Yes, maybe it is the config introduced problems, I build it with enable debug options.

Thanks!

Eric

#4

Hi, Ben
gcc version is: 4.7.0
clang version is: 3.2

The command options are:
1) clang
generated object files: clang -O3 -c *.c -o x.o
link: clang *.o -lm -o mpeg2enc

2) gcc
generated object files: gcc -O3 -c *.c -o x.o
link: gcc *.o -lm -o mpeg2enc

Yes, maybe it is the config introduced problems, I build it with enable
debug options.

More the point did you build it optimized or unoptimized. Can you show
your configure/make commands?

-eric

#5

The options is
cmake -DCMAKE_BUILD_TYPE=“Debug” -DCMAKE_INSTALL_PREFIX=~software/llvmsvn -DCMAKE_EXPORT_COMPILE_COMMANDS=ON /home/xxx/lsoftware/llvm-3.2-svn

$make
$make install

#6

-Eli

#7

From: llvmdev-bounces@cs.uiuc.edu [mailto:llvmdev-bounces@cs.uiuc.edu]
On Behalf Of Eli Friedman
Subject: Re: [LLVMdev] does clang and llvm take more time to compile c code

That would do it; Debug builds are roughly 2x slower than Release builds.

We've found the ratio to be much higher than that - approaching 10x when compiling something with high optimization levels.

- Chuck

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