llvm dev - Nov 2015 - How does -fPIE get passed from clang to llc when run on a .ll file?

If I create an llvm IR file (.ll) using clang like this:

  clang -v -emit-llvm -fPIC -O0 -S global_dat.c -o global_dat_x86_pic.ll

And then take a look at the resulting .ll file, I see near the bottom:

  !0 = !{i32 1, !"PIC Level", i32 2}

Now if I do the same, but specify -fPIE:

  clang -v -emit-llvm -fPIE -O0 -S global_dat.c -o global_dat_x86_pie.ll

And then look at the resulting global_dat_x86_pie.ll file, I see it is
identical to the one where I specified -fPIC (global_dat_x86_pic.ll).
There's no indication of the PIE level in the .ll file.

However, I can see (based on the verbose output) that the PIE Level should
be 2:

   "clang-3.6" -cc1 -triple xstg--linux-elf -emit-llvm -disable-free
-main-file-name global_dat.c -mrelocation-model pic -pic-level 2 -pie-level
2 ...

So if I were to pass this .ll file (global_dat_x86_pie.ll) to llc how would
llc know that the PIE Level is 2? Is this an oversight, bug, or expetcted
behaviour with a different workaround?
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On 6 November 2015 at 10:32, Phil Tomson via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> So if I were to pass this .ll file (global_dat_x86_pie.ll) to llc how would
> llc know that the PIE Level is 2? Is this an oversight, bug, or expetcted
> behaviour with a different workaround?
It looks like it's the "-enable-pie" command line option, which
gets
hooked up to TargetOptions::PositionIndependentExecutable if you're
doing it programmatically. I'm not sure of the history behind why
they're different though, I'm afraid.

Tim.

On Fri, Nov 6, 2015 at 10:46 AM, Tim Northover <t.p.northover at
gmail.com>
wrote:
> On 6 November 2015 at 10:32, Phil Tomson via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > So if I were to pass this .ll file (global_dat_x86_pie.ll) to llc how
> would
> > llc know that the PIE Level is 2? Is this an oversight, bug, or
expetcted
> > behaviour with a different workaround?
>
> It looks like it's the "-enable-pie" command line option,
which gets
> hooked up to TargetOptions::PositionIndependentExecutable if you're
> doing it programmatically. I'm not sure of the history behind why
> they're different though, I'm afraid.
>
>
With 3.6 I get an unused argument warning with -enable-pie:

$ clang -v -emit-llvm -enable-pie -O0 -S global_dat.c -o
global_dat_x86_pie.ll

clang: warning: argument unused during compilation: '-e nable-pie'
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