https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70574
Bug ID: 70574 Summary: [5/6 Regression] wrong code with -mavx2, read of partially initialised stack variable Product: gcc Version: unknown 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: --- Target: x86_64-pc-linux-gnu Created attachment 38210 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=38210&action=edit reduced testcase Output: $ gcc -O -fPIC -frerun-cse-after-loop -fno-tree-ccp -mcmodel=medium -mavx2 testcase.c $ valgrind -q ./a.out ==1282== Conditional jump or move depends on uninitialised value(s) ==1282== at 0x400653: main (in /home/zso/gcc-bug/89/a.out) ==1282== Aborted The problem most likely is (intel sytax): ... foo: ... mov DWORD PTR -52[rbp], edi # %sfp, u64_0 mov QWORD PTR -64[rbp], rcx # %sfp, u128_1 1) mov BYTE PTR -48[rbp], -1 # %sfp, vpxor xmm2, xmm2, xmm2 # tmp120 2) vpinsrb xmm2, xmm2, BYTE PTR -48[rbp], 1 # tmp120, tmp120, %sfp, vmovd xmm4, DWORD PTR -64[rbp] # tmp124, %sfp mov eax, 0 # tmp126, vpinsrb xmm4, xmm4, eax, 1 # tmp125, tmp124, tmp126, 3) vmovd xmm3, DWORD PTR -48[rbp] # tmp129, %sfp ... 1 stores a "byte" -1, 2 reads "byte" -1, 3 reads "dword" -1 (3 bytes of garbage) $ gcc -v Using built-in specs. COLLECT_GCC=/repo/gcc-trunk/binary-latest/bin/x86_64-pc-linux-gnu-gcc COLLECT_LTO_WRAPPER=/repo/gcc-trunk/binary-trunk-234794-checking-yes-rtl-df-nographite/bin/../libexec/gcc/x86_64-pc-linux-gnu/6.0.0/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: /repo/gcc-trunk//configure --enable-languages=c,c++ --enable-checking=yes,rtl,df --without-cloog --without-ppl --without-isl --disable-libstdcxx-pch --prefix=/repo/gcc-trunk//binary-trunk-234794-checking-yes-rtl-df-nographite Thread model: posix gcc version 6.0.0 20160406 (experimental) (GCC)