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From: "yevh.kolesnikov at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug ipa/96482] [10/11 Regression] Combination of
 -finline-small-functions and ipa-cp optimisations causes incorrect values
 being passed to a function since r279523
Date: Mon, 10 Aug 2020 14:24:22 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96482

--- Comment #5 from Yevhenii Kolesnikov <yevh.kolesnikov at gmail dot com> =
---
(In reply to Martin Li=C5=A1ka from comment #3)
> Thank you for the report, I can take a look.
> Can you please provide steps how to build Mesa with -O3 and -flto?

mesa is configured with meson. LTO can be enabled with builtin option
-b_lto=3Dtrue. Options can be supplied to the compiler with -Dc_args and
-Dcpp_args. So, to enable O3 it's -Dc_args=3D"-O3" -Dcpp_args=3D"-O3". You'=
ll also
need to set -Dbuildtype=3Dplain, or otherwise these options will be overwri=
tten.=20

So, the full build process will look like this:

meson \
    -Dbuildtype=3Dplain \
    -Dvalgrind=3Dfalse \
    -Ddri-drivers=3Di965 \
    -Dgallium-drivers=3Diris,swrast \
    -Dvulkan-drivers=3D \
    -Dgallium-omx=3D"disabled" \
    -Dplatforms=3Dx11,drm,surfaceless \
    -Dllvm=3Dfalse \
    -Db_lto=3Dtrue \
    -Dc_args=3D"-g \
              -O3 \
              " \
    -Dcpp_args=3D"-g \
                -O3 \
                " \
    --prefix=3D~/builds/mesa-bug \
    ./mesa-bug

ninja -C ./mesa-bug install

The aforementioned functions and assembly code then will be in
~/builds/mesa-bug/lib/dri/iris_dri.so

> About the addr_to_index function: am I right that unreachable is defined =
in
> your configuration as __builtin_unreachable?

To be precise, unreachable is defined like this:

#define unreachable(str)    \
do {                        \
   assert(!str);            \
   __builtin_unreachable(); \
} while (0)

I'm not sure why this one-time loop is necessary, to be honest.

> Can you please replace it with fprintf that prints the value?

The value of addr_format? It doesn't print anything, since this branch is n=
ever
hit. Moreover, it prevents addr_to_index from being inlined, so the crash g=
oes
away. The value of addr_format in my case is 3, which corresponds to the
nir_address_format_32bit_index_offset enum. So, in my case, the first branc=
h is
always hit.=