FWIW I just realized it also enables -fmerge-constants which is enabled
at all optimize levels, and built/compared it with fmerge-all-constants.
The difference is still noticeable. If anybody interested, I can
pretty-format it, and send here.
On 25.07.2018 14:03, Konstantin Kharlamov wrote:
This is a standard non-conforming optimization, which, quoting,
"…considers e.g. even constant initialized arrays or initialized
constant variables with integral or floating-point types. Languages like
C or C++ require each variable, including multiple instances of the same
variable in recursive calls, to have distinct locations, so using this
option results in non-conforming behavior."
Having the same or distinct addresses of constants in recursive calls is
too obscure behavior to make any use of. More over, until 4 April 2018
clang have had this option enabled by default¹, and nobody ever noticed
until kernel build fail this year (having a low-level hackery in kernel
surprises no one), resulting in PR disabling the option by default.
As for Mesa: I personally have been using the option for release builds
since forever, never had any problems.
Real world significance, sizes of binaries in bytes:
default | -fmerge-all-constants
| diff
-----------------------------------------------------------------------------------------------------
8048024 <-> bellagio/libomx_mesa.so | 7867800 <->
bellagio/libomx_mesa.so | -180224
10209120 <-> d3d/d3dadapter9.so.1.0.0 | 10016608 <->
d3d/d3dadapter9.so.1.0.0 | -192512
14464936 <-> dri/i915_dri.so | 14383016 <-> dri/i915_dri.so
| -81920
16894344 <-> dri/kms_swrast_dri.so | 16644488 <->
dri/kms_swrast_dri.so | -249856
8077560 <-> dri/nouveau_drv_video.so | 7893240 <->
dri/nouveau_drv_video.so | -184320
3882872 <-> gallium-pipe/pipe_nouveau.so | 3870584 <->
gallium-pipe/pipe_nouveau.so | -12288
2511160 <-> gallium-pipe/pipe_r300.so | 2502968 <->
gallium-pipe/pipe_r300.so | -8192
2818520 <-> gallium-pipe/pipe_r600.so | 2810328 <->
gallium-pipe/pipe_r600.so | -8192
4123056 <-> gallium-pipe/pipe_radeonsi.so | 3955120 <->
gallium-pipe/pipe_radeonsi.so | -167936
2413936 <-> gallium-pipe/pipe_swrast.so | 2401648 <->
gallium-pipe/pipe_swrast.so | -12288
2701360 <-> gallium-pipe/pipe_vmwgfx.so | 2689072 <->
gallium-pipe/pipe_vmwgfx.so | -12288
582496 <-> libGLX_mesa.so.0.0.0 | 578400 <->
libGLX_mesa.so.0.0.0 | -4096
23451656 <-> libMesaOpenCL.so.1.0.0 | 23447560 <->
libMesaOpenCL.so.1.0.0 | -4096
10370344 <-> libOSMesa.so.8.0.0 | 10300712 <-> libOSMesa.so.8.0.0
| -69632
4766032 <-> libvulkan_intel.so | 4745552 <-> libvulkan_intel.so
| -20480
2761376 <-> libvulkan_radeon.so | 2753184 <->
libvulkan_radeon.so | -8192
4703776 <-> libxatracker.so.2.4.0 | 4687392 <->
libxatracker.so.2.4.0 | -16384
8510392 <-> vdpau/libvdpau_nouveau.so.1.0.0 | 8326072 <->
vdpau/libvdpau_nouveau.so.1.0.0 | -184320
For consistency it's enabled for both debug and release builds.
1: https://reviews.llvm.org/D45289
Signed-off-by: Konstantin Kharlamov <hi-an...@yandex.ru>
---
meson.build | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/meson.build b/meson.build
index e05645cbf3..36016cf959 100644
--- a/meson.build
+++ b/meson.build
@@ -794,6 +794,11 @@ foreach a : ['-Wall', '-fno-math-errno',
'-fno-trapping-math',
endif
endforeach
+if ['gcc', 'clang'].contains(cc.get_id())
+ c_args += '-fmerge-all-constants'
+ cpp_args += '-fmerge-all-constants'
+endif
+
# For some reason, the test for -Wno-foo always succeeds with gcc, even if the
# option is not supported. Hence, check for -Wfoo instead.
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