[LLVMdev] speed and code size issues

[Daniel Dunbar]

Hi Jonathan,

Please pick one or two files you think are representative of the file
size problem and file bugs with the preprocessed inputs and command
line here:
http://llvm.org/bugs

As for the compile performance, its hard to do much with those full
build numbers. Can you see if the problem manifests itself with some
individual file, and file a bug if so (please include preprocessed
input and command lines)? Given the difference in code size, llvm-gcc
and clang would appear to be doing more work, so that will of course
negatively impact build times. However, I'm still surprised by your
times and would be happy to investigate if you can get me a test case.

 - Daniel

On Fri, Jul 17, 2009 at 4:14 PM, Jonathan Gray<jsg at goblin.cx> wrote:
> So it would appear that llvm-gcc and clang are both slower than
> gcc4 which is infamous for being slow at compiling code, and
> yes this is with a release build/--enable-optimizations.
>
> This seems to go against notes such as
> http://clang.llvm.org/features.html#performance
> which claim clang is signifcantly faster than gcc.
>
> Below are some times and the larger object files when
> compiling an i386 OpenBSD kernel at -O2 on an Intel Atom
> based laptop.  The significantly larger code size
> is rather disturbing as it means binaries can't fit on
> space constrained installation media for example.
>
> As the large object files appear with both llvm-gcc
> and clang it would appear to be a problem with
> the X86 backend.  Is this the expected behaviour at
> this point?  There is quite a difference in code size
> between llvm based compilers and pure GCC ones.
>
> I'm happy to supply more configuration/object size details
> if someone is interested.
>
> =========================
>
> clang 20070717 svn --enable-optimizations
> text    data    bss     dec     hex
> 7412287 160516  1049460 8622263 8390b7
>   19m4.11s real    16m56.35s user     1m44.23s system
>
> -rw-r--r--  1 jsg  wsrc   122K Jul 18 01:41 if_spppsubr.o
> -rw-r--r--  1 jsg  wsrc   127K Jul 18 01:36 aic79xx.o
> -rw-r--r--  1 jsg  wsrc   130K Jul 18 01:46 pci_subr.o
> -rw-r--r--  1 jsg  wsrc   161K Jul 18 01:38 bwi.o
> -rw-r--r--  1 jsg  wsrc   349K Jul 18 01:47 isp_pci.o
> -rwxr-xr-x  1 jsg  wsrc   7.9M Jul 18 01:54 bsd
>
> =========================
>
> gcc 3.3.5
>
> text    data    bss     dec     hex
> 6358820 182268  1051044 7592132 73d8c4
>   14m7.04s real    13m5.64s user     1m15.96s system
>
> -rw-r--r--  1 jsg  wsrc  85.2K Jul 18 02:25 isp.o
> -rw-r--r--  1 jsg  wsrc  97.5K Jul 18 02:26 bwi.o
> -rw-r--r--  1 jsg  wsrc   100K Jul 18 02:24 aic79xx.o
> -rw-r--r--  1 jsg  wsrc   124K Jul 18 02:32 pci_subr.o
> -rw-r--r--  1 jsg  wsrc   350K Jul 18 02:32 isp_pci.o
> -rwxr-xr-x  1 jsg  wsrc   6.9M Jul 18 02:38 bsd
>
> =========================
>
> gcc 4.2.4
>
> text    data    bss     dec     hex
> 6373332 169212  1051044 7593588 73de74
>   17m49.36s real    16m44.82s user     1m15.59s system
>
> -rw-r--r--  1 jsg  wsrc  98.6K Jul 18 02:00 aic79xx.o
> -rw-r--r--  1 jsg  wsrc  99.3K Jul 18 02:02 bwi.o
> -rw-r--r--  1 jsg  wsrc   124K Jul 18 02:09 pci_subr.o
> -rw-r--r--  1 jsg  wsrc   351K Jul 18 02:10 isp_pci.o
> -rwxr-xr-x  1 jsg  wsrc   6.9M Jul 18 02:17 bsd
>
> =========================
>
> llvm-gcc 4.2.1 svn 20090717
>
> gcc version 4.2.1 (Based on Apple Inc. build 5646) (LLVM build)
>
> ld -Ttext 0xD0200120 -e start -N --warn-common -S -x -o bsd ${SYSTEM_OBJ} vers.o
> text    data    bss     dec     hex
> 7235924 179256  1053092 8468272 813730
>   18m4.05s real    16m35.42s user     1m35.06s system
>
> -rw-r--r--  1 jsg  wsrc   118K Jul 18 01:12 if_spppsubr.o
> -rw-r--r--  1 jsg  wsrc   124K Jul 18 01:16 pci_subr.o
> -rw-r--r--  1 jsg  wsrc   125K Jul 18 01:07 aic79xx.o
> -rw-r--r--  1 jsg  wsrc   159K Jul 18 01:09 bwi.o
> -rw-r--r--  1 jsg  wsrc   349K Jul 18 01:17 isp_pci.o
> -rwxr-xr-x  1 jsg  wsrc   7.8M Jul 18 01:24 bsd
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