Fix build of optimized functions with LTO

[viccie30]

When building zlib-ng with LTO enabled, at least GCC doesn't respect the flags of each source file and just throws all the flags together. See https://gcc.gnu.org/onlinedocs/gccint/LTO-object-file-layout.html.

Because of this, flags don't get applied correctly to the arch-specific files, leading to problems like #722.

CMake does not allow disabling LTO per source file, so in CMakeLists.txt I just added -fno-lto if the compiler is GCC-like and native mode is not enabled.
For the configure script I wrote the same logic, but using an extra variable in arch/*/Makefile.in.

[codecov]

Codecov Report

Merging #938 (60b6d2d) into develop (f03918f) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop     #938      +/-   ##
===========================================
- Coverage    77.89%   77.88%   -0.02%     
===========================================
  Files           74       74              
  Lines         8307     8303       -4     
  Branches      1369     1374       +5     
===========================================
- Hits          6471     6467       -4     
  Misses        1307     1307              
  Partials       529      529              

Flag	Coverage Δ
macos_clang	68.65% <ø> (ø)
macos_gcc	67.64% <ø> (ø)
ubuntu_clang	73.51% <ø> (-1.68%)	⬇️
ubuntu_clang_debug	73.81% <ø> (-1.62%)	⬇️
ubuntu_clang_inflate_allow_invalid_dist	73.24% <ø> (-1.68%)	⬇️
ubuntu_clang_inflate_strict	73.51% <ø> (-1.68%)	⬇️
ubuntu_clang_mmap	73.22% <ø> (-1.67%)	⬇️
ubuntu_clang_msan	73.51% <ø> (-1.68%)	⬇️
ubuntu_gcc	73.16% <ø> (-1.43%)	⬇️
ubuntu_gcc_aarch64	74.46% <ø> (+0.25%)	⬆️
ubuntu_gcc_aarch64_compat_no_opt	74.00% <ø> (+0.38%)	⬆️
ubuntu_gcc_aarch64_no_acle	74.28% <ø> (+0.36%)	⬆️
ubuntu_gcc_aarch64_no_neon	74.03% <ø> (+0.36%)	⬆️
ubuntu_gcc_armhf	75.15% <ø> (+0.25%)	⬆️
ubuntu_gcc_armhf_compat_no_opt	74.02% <ø> (+0.38%)	⬆️
ubuntu_gcc_armhf_no_acle	75.34% <ø> (+0.25%)	⬆️
ubuntu_gcc_armhf_no_neon	75.72% <ø> (+0.26%)	⬆️
ubuntu_gcc_armsf	75.16% <ø> (+0.25%)	⬆️
ubuntu_gcc_armsf_compat_no_opt	74.02% <ø> (+0.38%)	⬆️
ubuntu_gcc_compat_no_opt	75.10% <ø> (+0.26%)	⬆️
ubuntu_gcc_mingw_i686	0.00% <ø> (ø)
ubuntu_gcc_mingw_x86_64	0.00% <ø> (ø)
ubuntu_gcc_no_avx2	75.14% <ø> (+0.35%)	⬆️
ubuntu_gcc_no_pclmulqdq	71.61% <ø> (-1.35%)	⬇️
ubuntu_gcc_no_sse2	74.10% <ø> (+0.05%)	⬆️
ubuntu_gcc_no_sse4	71.58% <ø> (-1.36%)	⬇️
ubuntu_gcc_o3	73.05% <ø> (-1.45%)	⬇️
ubuntu_gcc_osb	75.99% <ø> (-1.31%)	⬇️
ubuntu_gcc_ppc	75.46% <ø> (+0.23%)	⬆️
ubuntu_gcc_ppc64	76.23% <ø> (+0.23%)	⬆️
ubuntu_gcc_ppc64le	74.98% <ø> (+0.26%)	⬆️
ubuntu_gcc_s390x	73.84% <ø> (+0.18%)	⬆️
ubuntu_gcc_sparc64	76.70% <ø> (+0.24%)	⬆️
win64_gcc	70.63% <ø> (ø)
win64_gcc_compat_no_opt	74.16% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
chunkset_tpl.h	95.14% <0.00%> (-3.89%)	⬇️
deflate.h	57.14% <0.00%> (+7.14%)	⬆️

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[viccie30]

I tested this patch using sbuild on all supported Debian architectures (amd64, arm64, armel, armhf, i386, mips64el, mipsel, ppc64el, and s390x) on stable, testing, unstable, and experimental, both with and without LTO and for static and shared builds.

For all combinations, except mips64el and mipsel on experimental due to dependency breakage, the builds succeed and all tests pass (using qemu-user-static for the non-x86 architectures).

[Dead2]

I think this override should perhaps not be active if the user enables Native mode, native is obviously useless for redistribution such as in distros, but it can be useful for those who compile locally and want the (possibly) fastest end result.

When native mode is enabled, all files are compiled with the same flags, essentially enabling all instruction sets the local cpu supports, so that should allow it to work with LTO.

[viccie30]

I agree, that's why both in configure and CMakeLists.txt the no lto flag is only defined if native mode is disabled

[Dead2]

Hah, indeed it is, I didn't notice that. 👍

[viccie30]

It took me a few tries to get that right as well, but I think I did the right way round