http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57051
Bug #: 57051 Summary: Optimization regression in 4.8.0 from 4.7.2 Classification: Unclassified Product: gcc Version: unknown Status: UNCONFIRMED Severity: normal Priority: P3 Component: c AssignedTo: unassig...@gcc.gnu.org ReportedBy: tony.howard-co84u...@yopmail.com The problem can be exhibited using the following snippet of code: /* begin */ int total = 0; inline void foo(int bar) { total += bar*10; } void hello() { for(int i = 0; i < 10; ++i) { foo(i); } } /* end */ With the option -O3, gcc 4.7.2 and previous versions produce the following assembly code: hello(): addl $450, total(%rip) ret gcc 4.8.0 fails to optimize the code: hello(): movdqa .LC0(%rip), %xmm0 movdqa %xmm0, %xmm2 psrldq $8, %xmm2 paddd %xmm2, %xmm0 movdqa %xmm0, %xmm3 psrldq $4, %xmm3 paddd %xmm3, %xmm0 movdqa %xmm0, %xmm4 movd %xmm4, -12(%rsp) movl -12(%rsp), %eax addl total(%rip), %eax addl $170, %eax movl %eax, total(%rip) ret The results can be easily reproduced using http://gcc.godbolt.org/ The 4.7.2's configure options are: Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.7.2-11precise2' --with-bugurl=file:///usr/share/doc/gcc-4.7/README.Bugs --enable-languages=c,c++,go,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.7 --enable-shared --enable-linker-build-id --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.7 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin --enable-objc-gc --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu The 4.8.0's configure options are: Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu/Linaro 4.8.0-3ubuntu3~12.04' --with-bugurl=file:///usr/share/doc/gcc-4.8/README.Bugs --enable-languages=c,c++,go,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.8 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.8 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin --with-system-zlib --enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu The problem is not linked to Linaro or Ubuntu patches as it can be reproduced as well on a stock version of gcc 4.8.0