[Scummvm-tracker] [ScummVM :: Bugs] #15039: Build fails with strict-aliasing violations

[ScummVM :: Bugs]

#15039: Build fails with strict-aliasing violations
-------------------------+--------------------
Reporter:  eli-schwartz  |      Owner:  (none)
    Type:  defect        |     Status:  new
Priority:  normal        |  Component:  Tools
 Version:                |   Keywords:
    Game:                |
-------------------------+--------------------
 I tried to compile with LTO: `-flto=4 -Werror=odr -Werror=lto-type-
 mismatch -Werror=strict-aliasing`

 The -Werror=* flags are important to detect cases where the compiler can
 try to optimize based on assuming UB cannot happen, and miscompile code
 that has UB in it. strict-aliasing issues are always bad but LTO can make
 them even worse.

 I got this error:
 {{{
 x86_64-pc-linux-gnu-g++ -MMD -MF "engines/grim/luac/.deps/dump.d" -MQ
 "engines/grim/luac/dump.o" -MP -Wall -march=native -fstack-protector-all
 -O2 -pipe -fdiagnostics-color=always -frecord-gcc-switches
 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=3 -fstack-clash-protection -flto=4
 -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing  -Wformat
 -Werror=format-security  -DNDEBUG -g -W -Wno-unused-parameter -Wno-empty-
 body -std=c++11  -I/usr/include/freetype2 -I/usr/include/harfbuzz
 -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -Wno-long-long -Wno-
 multichar -Wno-unknown-pragmas -Wno-reorder -Wpointer-arith -Wcast-qual
 -Wshadow -Wnon-virtual-dtor -Wwrite-strings -fcheck-new -DHAVE_CONFIG_H
 -DPOSIX -I. -I. -I/usr/include/libpng16  -c engines/grim/luac/dump.cpp -o
 engines/grim/luac/dump.o
 engines/grim/luac/dump.cpp: In function ‘void DumpFloat(float, FILE*)’:
 engines/grim/luac/dump.cpp:31:31: error: dereferencing type-punned pointer
 will break strict-aliasing rules [-Werror=strict-aliasing]
    31 |         WRITE_LE_UINT32(out, *(uint32*)(&f));
       |                               ^~~~~~~~~~~~~
 cc1plus: some warnings being treated as errors
 make: *** [Makefile.common:531: engines/grim/luac/dump.o] Error 1
 }}}


 Downstream report: https://bugs.gentoo.org/926081
-- 
Ticket URL: <https://bugs.scummvm.org/ticket/15039>
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