[LLVMdev] speed and code size issues

Jonathan Gray jsg at goblin.cx
Fri Jul 17 17:12:57 PDT 2009

On Fri, Jul 17, 2009 at 04:41:55PM -0700, Eli Friedman wrote:
> On Fri, Jul 17, 2009 at 4:14 PM, Jonathan Gray<jsg at goblin.cx> wrote:
> > This seems to go against notes such as
> > http://clang.llvm.org/features.html#performance
> > which claim clang is signifcantly faster than gcc.
> I think the URL you want is actually
> http://clang.llvm.org/performance.html.  The difference isn't as
> dramatic when you consider code generation, at least for the moment.

Are these scripts to break down the time spent
in different stages available somewhere?

> > 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.
> Are you building with -g?  The debug info implementation is known to
> be relatively inefficient.

No -g/debug info, as below with additional -D defines.

-Wall -Wstrict-prototypes -Wmissing-prototypes  -Wno-uninitialized -Wno-format
-fno-builtin -fno-zero-initialized-in-bss  -mno-mmx -mno-sse -mno-sse2 -mno-sse3
-O2 -pipe -nostdinc

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