[LLVMdev] LTO v. opt

[Sean Silva]

tools/llvm-lto should get you pretty close.

On Fri, Jan 2, 2015 at 8:32 PM, David Callahan <dcallahan at fb.com> wrote:

>  Hi,
>
>
>
> I am new to the LLVM dev community so forgive a perhaps obvious question.
> I am looking at bug 17623 which is an LTO/optimizer interaction bug.  I am
> working on a Mac with Xcode installed but have also built the 3.6 LLVM
> binaries (from a few month old local branch).
>
>
>
> The default version of “ld” from Apple supports an option “-save-temps”
> which I believe saves bitcode both before and after the optimizer (and the
> bug is visible as a difference between these two)
>
>
>
> ~/llvm-install/bin/clang -flto -O2 -c -o bug17623.o bug17623.c
>
> "/usr/bin/ld" -demangle -dynamic -arch x86_64 -macosx_version_min 10.10.0
> -lSystem /Users/dcallahan/llvm-install/bin/..\
>
> /lib/clang/3.6.0/lib/darwin/libclang_rt.osx.a -save-temps -o bug36
> bug17623.o
>
>
>
> (this produces bug36.lto.bc and bug36.lto.opt.bc)
>
>
>
> However, if I use “opt” to try and duplicate the actions run by “ld”, as
> in:
>
>
>
> ~/llvm-install/bin/opt -O2 -o bug36.opt.bc bug36.lto.bc
>
>
>
> This generates a different (much cleaner and correct!) output.
>
>
>
> So my questions are:
>
> 1.     Is it feasible to get “opt” to reproduce the behavior of “ld”?
>
> 2.     Assuming I am just missing some parameters to “opt”, how do I
> determine what they should be?
>
> Thanks
>
> David
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20150105/6559e7a1/attachment.html>