Hi, everyone! I have some code which is giving strict-aliasing warnings on gcc 4.4.1, and I don't understand why. When I compile alias-warning2.c (attached), I get $ gcc -O2 -Wall alias-warning2.c -o alias-warning2 alias-warning2.c: In function 'main': alias-warning2.c:31: warning: dereferencing pointer 'd2.16' does break strict-aliasing rules alias-warning2.c:39: note: initialized from here and indeed, when I run, gcc has optimized out the offending code: $ ./alias-warning2 Aliasing is unhappy! d2.base.a == 5 However, as far as I can tell, at line 31 the object d2.base (which has type 'struct base') is indeed being accessed through a pointer of type 'struct base*'. If I change the inline function to take the type 'struct base*' directly, rather than 'union derived_union*', I do not get a warning, or mis-compilaton. Am I missing something, or is gcc mis-compiling correct code? $ gcc -v Using built-in specs. Target: i486-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.4.1-4ubuntu8' --with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs --enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared --enable-multiarch --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4 --program-suffix=-4.4 --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-objc-gc --enable-targets=all --disable-werror --with-arch-32=i486 --with-tune=generic --enable-checking=release --build=i486-linux-gnu --host=i486-linux-gnu --target=i486-linux-gnu Thread model: posix gcc version 4.4.1 (Ubuntu 4.4.1-4ubuntu8) -- Jonathan Lennox Vidyo, Inc jonathan@xxxxxxxxx
Attachment:
alias-warning2.c
Description: alias-warning2.c
