https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89815
Bug ID: 89815 Summary: [7/8/9 Regression] wrong code with -Og -march=armv4t -fno-tree-ccp -fno-tree-fre Product: gcc Version: 9.0 Status: UNCONFIRMED Keywords: wrong-code Severity: normal Priority: P3 Component: rtl-optimization Assignee: unassigned at gcc dot gnu.org Reporter: zsojka at seznam dot cz Target Milestone: --- Host: x86_64-pc-linux-gnu Target: armv7a-hardfloat-linux-gnueabi Created attachment 46017 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46017&action=edit reduced testcase Output: $ armv7a-hardfloat-linux-gnueabi-gcc -Og -march=armv4t -fno-tree-ccp -fno-tree-fre testcase.c -static $ ./a.out qemu: uncaught target signal 6 (Aborted) - core dumped Aborted Correct value is 0xff, wrong value is 0xffffffff. The wrong value seems to be generated by the instruction: ... @ testcase.c:10: b = __builtin_sub_overflow (0xff, (u8) - d, &f); mvn r4, #0 @ tmp143, ... $ armv7a-hardfloat-linux-gnueabi-gcc -v Using built-in specs. COLLECT_GCC=/repo/gcc-trunk/binary-latest-armv7a-hardfloat/bin/armv7a-hardfloat-linux-gnueabi-gcc COLLECT_LTO_WRAPPER=/repo/gcc-trunk/binary-trunk-269905-checking-yes-rtl-df-extra-armv7a-hardfloat/bin/../libexec/gcc/armv7a-hardfloat-linux-gnueabi/9.0.1/lto-wrapper Target: armv7a-hardfloat-linux-gnueabi 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 --with-float=hard --with-fpu=vfpv4 --with-arch=armv7-a --with-sysroot=/usr/armv7a-hardfloat-linux-gnueabi --build=x86_64-pc-linux-gnu --host=x86_64-pc-linux-gnu --target=armv7a-hardfloat-linux-gnueabi --with-ld=/usr/bin/armv7a-hardfloat-linux-gnueabi-ld --with-as=/usr/bin/armv7a-hardfloat-linux-gnueabi-as --disable-libstdcxx-pch --prefix=/repo/gcc-trunk//binary-trunk-269905-checking-yes-rtl-df-extra-armv7a-hardfloat Thread model: posix gcc version 9.0.1 20190325 (experimental) (GCC) The .ira dump has: ... (insn 55 24 32 2 (set (reg:QI 145 [143]) (const_int -1 [0xffffffffffffffff])) "testcase.c":10:7 191 {*arm_movqi_insn} (nil)) ... (insn 58 43 47 2 (set (reg:QI 143) (reg:QI 145 [143])) "testcase.c":13:1 191 {*arm_movqi_insn} (expr_list:REG_DEAD (reg:QI 145 [143]) (nil))) (insn 47 58 48 2 (set (reg/i:SI 0 r0) (subreg:SI (reg:QI 143) 0)) "testcase.c":13:1 654 {*arm_movsi_vfp} (expr_list:REG_DEAD (reg:QI 143) (nil))) ... And the .reload dump has: ... (insn 55 24 32 2 (set (reg:QI 4 r4 [143]) (const_int -1 [0xffffffffffffffff])) "testcase.c":10:7 191 {*arm_movqi_insn} (nil)) ... (insn 58 43 48 2 (set (reg:QI 0 r0 [143]) (reg:QI 4 r4 [143])) "testcase.c":13:1 191 {*arm_movqi_insn} (nil)) ...