[LLVMdev] LLVM 3.4 performance regressed?

[Jonas Wagner]

Hi,

(adding llvm-dev again)

I did enable optimization, but that didn't have an effect on the runtime
> performance numbers.
>

Can you elaborate? For a program such as bzip2, I'd expect the program to
be at least twice as fast with -O3 than with -O0.

I also noticed that you use LLC in the final step. An alternative that
works well for me is to use the gold linker
plugin<http://llvm.org/docs/GoldPlugin.html>.
This way, you can link bitcode files directly into the program by using

    clang -flto $(LDFLAGS) <bitcode files> -o <output file> $(LDLIBS)

If your bitcode files have the extension .o, clang will only run LTO
optimizations, code generation, and linking. If they have the extension
.bc, it will run a full set of compilation passes (in which case you might
want to add $(CFLAGS) to the command line).

Hope this helps,
Jonas
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