[Bug 77580] GCC memory starvation caused by flatten attribute with LTO

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=77580

--- Comment #5 from Patrick McMunn <doctorwhoguy at gmail.com> ---
Created attachment 125089
  --> https://bugs.freedesktop.org/attachment.cgi?id=125089&action=edit
Patch to allow LTO optmization of xf86-video-intel

I'm attaching a patch that takes a somewhat simpler approach to disabling
"flatten" and "force_inline" which cause problems with LTO.

I used glxgears to measure FPS. The system was a Pentium 4 with an integrated
845G graphics chip, so it's pretty underpowered hardware, hence the low FPS.
Without LTO, I got ~19.5 FPS running glxgears at fullscreen at 1680x1050
resolution. With LTO, I got about 22.5 FPS. That may not seem like much, but
that's a 10% performance improvement! Except for the LTO-related flags, I used
the same compiler and linker flags during compilation.

flags used during compilation:

CFLAGS="-O2 -march=pentium4 -pipe -fdevirtualize-speculatively ${LTO}"
CXXFLAGS="${CFLAGS}"
LDFLAGS="-Wl,-O1 -Wl,--as-needed -Wl,--enable-new-dtags -Wl,--sort-common
-Wl,--sort-section=name -Wl,-Bsymbolic-functions -Wl,-z,combreloc ${CXXFLAGS}"

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