https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81633
Bug ID: 81633 Summary: Incorrect floating point result with tree vectoriser Product: gcc Version: 7.1.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: wence at gmx dot li Target Milestone: --- Created attachment 41873 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41873&action=edit Preprocessed source. The attached source (reduced from a real kernel) multiplies a 4x4 identity matrix by its first column, It should produce the output: 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 With GCC 7.1.0, (and a recent 8.0.0 snapshot) it produces instead: 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 The bug disappears if I say either -fno-tree-vectorize or -fno-tree-loop-vectorize $ gcc -o prog.exe -Wall -Wextra -std=c99 -pedantic -O3 -v prog.c Using built-in specs. COLLECT_GCC=/opt/wandbox/gcc-7.1.0/bin/gcc COLLECT_LTO_WRAPPER=/opt/wandbox/gcc-7.1.0/libexec/gcc/x86_64-pc-linux-gnu/7.1.0/lto-wrapper Target: x86_64-pc-linux-gnu Configured with: ../gcc-7.1.0/configure --prefix=/opt/wandbox/gcc-7.1.0 --enable-languages=c,c++ --disable-multilib --without-ppl --without-cloog-ppl --enable-checking=release --disable-nls LDFLAGS=-Wl,-rpath,/opt/wandbox/gcc-7.1.0/lib,-rpath,/opt/wandbox/gcc-7.1.0/lib64,-rpath,/opt/wandbox/gcc-7.1.0/lib32 --enable-lto Thread model: posix gcc version 7.1.0 (GCC) COLLECT_GCC_OPTIONS='-o' 'prog.exe' '-Wpedantic' '-std=c99' '-Wall' '-Wextra' '-O3' '-v' '-mtune=generic' '-march=x86-64' /opt/wandbox/gcc-7.1.0/libexec/gcc/x86_64-pc-linux-gnu/7.1.0/cc1 -quiet -v -imultiarch x86_64-linux-gnu prog.c -quiet -dumpbase prog.c -mtune=generic -march=x86-64 -auxbase prog -O3 -Wpedantic -Wall -Wextra -std=c99 -version -o /tmp/ccorXUPc.s GNU C99 (GCC) version 7.1.0 (x86_64-pc-linux-gnu) compiled by GNU C version 7.1.0, GMP version 6.1.0, MPFR version 3.1.4, MPC version 1.0.3, isl version none GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu" ignoring nonexistent directory "/usr/local/include" ignoring nonexistent directory "/opt/wandbox/gcc-7.1.0/lib/gcc/x86_64-pc-linux-gnu/7.1.0/../../../../x86_64-pc-linux-gnu/include" #include "..." search starts here: #include <...> search starts here: /opt/wandbox/gcc-7.1.0/lib/gcc/x86_64-pc-linux-gnu/7.1.0/include /opt/wandbox/gcc-7.1.0/include /opt/wandbox/gcc-7.1.0/lib/gcc/x86_64-pc-linux-gnu/7.1.0/include-fixed /usr/include/x86_64-linux-gnu /usr/include End of search list. GNU C99 (GCC) version 7.1.0 (x86_64-pc-linux-gnu) compiled by GNU C version 7.1.0, GMP version 6.1.0, MPFR version 3.1.4, MPC version 1.0.3, isl version none GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 Compiler executable checksum: 5122689c716743eb07fee255d0dfe7c4 COLLECT_GCC_OPTIONS='-o' 'prog.exe' '-Wpedantic' '-std=c99' '-Wall' '-Wextra' '-O3' '-v' '-mtune=generic' '-march=x86-64' as -v --64 -o /tmp/cc0c1aeA.o /tmp/ccorXUPc.s GNU assembler version 2.26.1 (x86_64-linux-gnu) using BFD version (GNU Binutils for Ubuntu) 2.26.1 COMPILER_PATH=/opt/wandbox/gcc-7.1.0/libexec/gcc/x86_64-pc-linux-gnu/7.1.0/:/opt/wandbox/gcc-7.1.0/libexec/gcc/x86_64-pc-linux-gnu/7.1.0/:/opt/wandbox/gcc-7.1.0/libexec/gcc/x86_64-pc-linux-gnu/:/opt/wandbox/gcc-7.1.0/lib/gcc/x86_64-pc-linux-gnu/7.1.0/:/opt/wandbox/gcc-7.1.0/lib/gcc/x86_64-pc-linux-gnu/ LIBRARY_PATH=/opt/wandbox/gcc-7.1.0/lib/gcc/x86_64-pc-linux-gnu/7.1.0/:/opt/wandbox/gcc-7.1.0/lib/gcc/x86_64-pc-linux-gnu/7.1.0/../../../../lib64/:/lib/x86_64-linux-gnu/:/lib/../lib64/:/usr/lib/x86_64-linux-gnu/:/opt/wandbox/gcc-7.1.0/lib/gcc/x86_64-pc-linux-gnu/7.1.0/../../../:/lib/:/usr/lib/ COLLECT_GCC_OPTIONS='-o' 'prog.exe' '-Wpedantic' '-std=c99' '-Wall' '-Wextra' '-O3' '-v' '-mtune=generic' '-march=x86-64' /opt/wandbox/gcc-7.1.0/libexec/gcc/x86_64-pc-linux-gnu/7.1.0/collect2 -plugin /opt/wandbox/gcc-7.1.0/libexec/gcc/x86_64-pc-linux-gnu/7.1.0/liblto_plugin.so -plugin-opt=/opt/wandbox/gcc-7.1.0/libexec/gcc/x86_64-pc-linux-gnu/7.1.0/lto-wrapper -plugin-opt=-fresolution=/tmp/ccfS7LEX.res -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lgcc_s -plugin-opt=-pass-through=-lc -plugin-opt=-pass-through=-lgcc -plugin-opt=-pass-through=-lgcc_s --eh-frame-hdr -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o prog.exe /usr/lib/x86_64-linux-gnu/crt1.o /usr/lib/x86_64-linux-gnu/crti.o /opt/wandbox/gcc-7.1.0/lib/gcc/x86_64-pc-linux-gnu/7.1.0/crtbegin.o -L/opt/wandbox/gcc-7.1.0/lib/gcc/x86_64-pc-linux-gnu/7.1.0 -L/opt/wandbox/gcc-7.1.0/lib/gcc/x86_64-pc-linux-gnu/7.1.0/../../../../lib64 -L/lib/x86_64-linux-gnu -L/lib/../lib64 -L/usr/lib/x86_64-linux-gnu -L/opt/wandbox/gcc-7.1.0/lib/gcc/x86_64-pc-linux-gnu/7.1.0/../../.. -rpath /opt/wandbox/gcc-7.1.0/lib64 /tmp/cc0c1aeA.o -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /opt/wandbox/gcc-7.1.0/lib/gcc/x86_64-pc-linux-gnu/7.1.0/crtend.o /usr/lib/x86_64-linux-gnu/crtn.o COLLECT_GCC_OPTIONS='-o' 'prog.exe' '-Wpedantic' '-std=c99' '-Wall' '-Wextra' '-O3' '-v' '-mtune=generic' '-march=x86-64' $ ./prog.exe 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0