[llvm-bugs] [Bug 39105] New: LLVM_LINK_LLVM_DYLIB builds are 5~8% slower

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=39105

            Bug ID: 39105
           Summary: LLVM_LINK_LLVM_DYLIB builds are 5~8% slower
           Product: new-bugs
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: mh+llvm at glandium.org
                CC: llvm-bugs at lists.llvm.org

For Firefox builds, we used to build clang without LLVM_LINK_LLVM_DYLIB and
recently switched it on to make the archive that is installed on every build
smaller (and faster to install). Anyways, the result of this change is that
building Firefox became between 5 and 8% slower as a consequence, which is
rather large (especially considering a large portion of build time is spent
doing things that aren't compiling C/C++).

It turns out this is because libLLVM exports a lot of symbols, and internal use
of those symbols all go through the PLT, increasing intra-libLLVM function call
overhead significantly.

FWIW, linking with -Wl,-Bsymbolic alleviates this.

-- 
You are receiving this mail because:
You are on the CC list for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-bugs/attachments/20180927/5ba50249/attachment.html>