https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86386
Bug ID: 86386 Summary: [8/9 Regression] unaligned load from stack with -Os -fno-tree-dce -mstringop-strategy=vector_loop -mavx512bw Product: gcc Version: 9.0 Status: UNCONFIRMED Keywords: wrong-code Severity: normal Priority: P3 Component: target Assignee: unassigned at gcc dot gnu.org Reporter: zsojka at seznam dot cz Target Milestone: --- Host: x86_64-pc-linux-gnu Target: x86_64-pc-linux-gnu Created attachment 44346 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=44346&action=edit reduced testcase I am not 100% sure the testcase has defined behavior (due to the cast to char*), but there are no compilation warning and -fsanitize=undefined does not give any error. Output: $ x86_64-pc-linux-gnu-gcc -Os -fno-tree-dce -mstringop-strategy=vector_loop -mavx512bw testcase.c $ ./a.out Segmentation fault Program received signal SIGSEGV, Segmentation fault. 0x0000000000400529 in a (g=g@entry=0 '\000', h=h@entry=0, i=i@entry=0, j=j@entry=0, k=k@entry=0 '\000', l=l@entry=4, m=1, n=<optimized out>) at testcase.c:14 14 __builtin_memcpy (&m, 2 + (char *) &n, 1); 0x000000000040051f <+61>: mov -0x8(%rsp),%rcx 0x0000000000400524 <+66>: mov %rax,-0x10(%rsp) => 0x0000000000400529 <+71>: vmovdqa -0x10(%rsp),%xmm0 0x000000000040052f <+77>: mov -0x10(%rsp),%rax 0x0000000000400534 <+82>: vpextrb $0x2,%xmm0,0x10(%rbp) (gdb) p $rsp $1 = (void *) 0x7fffffffd648 $ x86_64-pc-linux-gnu-gcc -v Using built-in specs. COLLECT_GCC=/repo/gcc-trunk/binary-latest-amd64/bin/x86_64-pc-linux-gnu-gcc COLLECT_LTO_WRAPPER=/repo/gcc-trunk/binary-trunk-262329-checking-yes-rtl-df-extra-nobootstrap-amd64/bin/../libexec/gcc/x86_64-pc-linux-gnu/9.0.0/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: /repo/gcc-trunk//configure --enable-languages=c,c++ --enable-valgrind-annotations --disable-nls --enable-checking=yes,rtl,df,extra --disable-bootstrap --with-cloog --with-ppl --with-isl --build=x86_64-pc-linux-gnu --host=x86_64-pc-linux-gnu --target=x86_64-pc-linux-gnu --with-ld=/usr/bin/x86_64-pc-linux-gnu-ld --with-as=/usr/bin/x86_64-pc-linux-gnu-as --disable-libstdcxx-pch --prefix=/repo/gcc-trunk//binary-trunk-262329-checking-yes-rtl-df-extra-nobootstrap-amd64 Thread model: posix gcc version 9.0.0 20180703 (experimental) (GCC)