https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85090
Bug ID: 85090 Summary: wrong code with -O2 -fno-tree-dominator-opts -mavx512f -fira-algorithm=priority Product: gcc Version: 8.0 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 43766 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43766&action=edit reduced testcase Compiler output: $ x86_64-pc-linux-gnu-gcc -O2 -fno-tree-dominator-opts -mavx512f -fira-algorithm=priority testcase.c $ sde64 -- ./a.out Aborted The value of x[] is "0000 0001 0002 0003 0000 0000 0000 0000 ...." instead of "0000 0001 0002 0003 0004 0005 0006 0007 ...." In the assembly output: ... # testcase.c:13: i[0] <<= 1; mov QWORD PTR [rsp+264], rax # %sfp, tmp4040 vmovq xmm20, QWORD PTR [rsp+264] # i, %sfp # testcase.c:14: e = (7 & -d) << (7 & -(g & 7)); ... vmovq zeroes the high-order bits of zmm20 - and that's where the zeroes come from. $ 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-258852-checking-yes-rtl-df-extra-amd64/bin/../libexec/gcc/x86_64-pc-linux-gnu/8.0.1/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 --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-258852-checking-yes-rtl-df-extra-amd64 Thread model: posix gcc version 8.0.1 20180326 (experimental) (GCC) Tested revisions: r258852 - FAIL 7-branch r258647 - OK