http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60233
Bug ID: 60233 Summary: AVX instructions emitted with -march=native on host without AVX support Product: gcc Version: 4.8.2 Status: UNCONFIRMED Severity: normal Priority: P3 Component: driver Assignee: unassigned at gcc dot gnu.org Reporter: steven at uplinklabs dot net Host: x86_64-unknown-linux-gnu Target: x86_64-unknown-linux-gnu Build: x86_64-unknown-linux-gnu Running GCC in a paravirtual Xen guest on an Ivy Bridge host. The PV guest does not have AVX support, and -march=native seems to detect this correctly: $ gcc -O2 -march=native -E -v - </dev/null 2>&1 | grep cc1 /usr/lib/gcc/x86_64-unknown-linux-gnu/4.8.2/cc1 -E -quiet -v - -march=core-avx-i -mcx16 -msahf -mno-movbe -maes -mpclmul -mpopcnt -mno-abm -mno-lwp -mno-fma -mno-fma4 -mno-xop -mno-bmi -mno-bmi2 -mno-tbm -mno-avx -mno-avx2 -msse4.2 -msse4.1 -mno-lzcnt -mno-rtm -mno-hle -mrdrnd -mf16c -mfsgsbase -mno-rdseed -mno-prfchw -mno-adx -mfxsr -mno-xsave -mno-xsaveopt --param l1-cache-size=32 --param l1-cache-line-size=64 --param l2-cache-size=25600 -mtune=core-avx-i -O2 Note in particular the -mno-avx and -mno-xsave. However, GCC is still emitting AVX instructions: $ cat vadd8.c typedef float v8f __attribute__ ((vector_size(32), aligned(1))); void vadd8f(v8f *o, v8f *a, v8f *b) { *o = *a + *b; } $ echo | gcc -dM -E - -march=native | grep AVX #define __AVX__ 1 $ gcc -O2 -march=native -c vadd8.c $ objdump -S vadd8.o vadd8.o: file format elf64-x86-64 Disassembly of section .text: 0000000000000000 <vadd8f>: 0: c5 f8 10 0e vmovups (%rsi),%xmm1 4: c5 f8 10 02 vmovups (%rdx),%xmm0 8: c4 e3 75 18 4e 10 01 vinsertf128 $0x1,0x10(%rsi),%ymm1,%ymm1 f: c4 e3 7d 18 42 10 01 vinsertf128 $0x1,0x10(%rdx),%ymm0,%ymm0 16: c5 f4 58 c0 vaddps %ymm0,%ymm1,%ymm0 1a: c5 f8 11 07 vmovups %xmm0,(%rdi) 1e: c4 e3 7d 19 47 10 01 vextractf128 $0x1,%ymm0,0x10(%rdi) 25: c5 f8 77 vzeroupper 28: c3 retq I'm guessing that the -march=core-avx-i it decided on is overriding the -mno-avx flag, but this seems to be a regression to me. Version information: $ gcc -v Using built-in specs. COLLECT_GCC=gcc COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-unknown-linux-gnu/4.8.2/lto-wrapper Target: x86_64-unknown-linux-gnu Configured with: /build/gcc/src/gcc-4.8-20140206/configure --prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/ --enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-shared --enable-threads=posix --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-clocale=gnu --disable-libstdcxx-pch --disable-libssp --enable-gnu-unique-object --enable-linker-build-id --enable-cloog-backend=isl --disable-cloog-version-check --enable-lto --enable-plugin --enable-install-libiberty --with-linker-hash-style=gnu --disable-multilib --disable-werror --enable-checking=release Thread model: posix gcc version 4.8.2 20140206 (prerelease) (GCC)