https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104763
Bug ID: 104763 Summary: [12.0] Generate wrong assembly code Product: gcc Version: 12.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: 570070308 at qq dot com Target Milestone: --- file test.c: ``` #include <stddef.h> #include <stdbool.h> #include <stdint.h> void move_up() { for ( size_t* i=(size_t *)(0xb8000+160*24); ; ) { *i=0x0700070007000700; //if ( i == (size_t *)(0xb8000+160*24+7*sizeof(size_t)) ) if ( i == (volatile size_t *)(0xb8000+160*24)+2 ) { break; } ++i; } while (1){} } ``` compile with `gcc -O1 test.c -S` or -O2 or -O3 the assemble code: ``` move_up: .LFB0: .cfi_startproc endbr64 movabsq $504410854964332288, %rax movq %rax, 757512 movq %rax, 757520 .L2: jmp .L2 .cfi_endproc ``` But the correct assembly code should be: ``` move_up: movabsq $504410854964332288, %rax movq %rax, 757504 movq %rax, 757512 movq %rax, 757520 .L2: jmp .L2 ``` I try to compile with -fno-strict-aliasing -fwrapv -fno-aggressive-loop-optimizations -Wall -Wextra and the result is same. This is the full gcc compile info: ``` ig@ig-virtual-machine:~/os/myos/temp$ gcc -O1 test.c -S -v Using built-in specs. COLLECT_GCC=gcc OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa OFFLOAD_TARGET_DEFAULT=1 Target: x86_64-linux-gnu Configured with: ../src/configure -v --with-pkgversion='Ubuntu 12-20220222-1ubuntu1' --with-bugurl=file:///usr/share/doc/gcc-12/README.Bugs --enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2 --prefix=/usr --with-gcc-major-version-only --program-suffix=-12 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib --enable-libphobos-checking=release --with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch --disable-werror --enable-cet --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none=/build/gcc-12-TT8eTw/gcc-12-12-20220222/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-12-TT8eTw/gcc-12-12-20220222/debian/tmp-gcn/usr --enable-offload-defaulted --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu Thread model: posix Supported LTO compression algorithms: zlib zstd gcc version 12.0.1 20220222 (experimental) [master r12-7325-g2f59f067610] (Ubuntu 12-20220222-1ubuntu1) COLLECT_GCC_OPTIONS='-O1' '-S' '-v' '-mtune=generic' '-march=x86-64' /usr/lib/gcc/x86_64-linux-gnu/12/cc1 -quiet -v -imultiarch x86_64-linux-gnu test.c -quiet -dumpbase test.c -dumpbase-ext .c -mtune=generic -march=x86-64 -O1 -version -o test.s -fasynchronous-unwind-tables -fstack-protector-strong -Wformat -Wformat-security -fstack-clash-protection -fcf-protection GNU C17 (Ubuntu 12-20220222-1ubuntu1) version 12.0.1 20220222 (experimental) [master r12-7325-g2f59f067610] (x86_64-linux-gnu) compiled by GNU C version 12.0.1 20220222 (experimental) [master r12-7325-g2f59f067610], GMP version 6.2.1, MPFR version 4.1.0, MPC version 1.2.1, isl version isl-0.24-GMP 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/lib/gcc/x86_64-linux-gnu/12/include-fixed" ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/12/../../../../x86_64-linux-gnu/include" #include "..." search starts here: #include <...> search starts here: /usr/lib/gcc/x86_64-linux-gnu/12/include /usr/local/include /usr/include/x86_64-linux-gnu /usr/include End of search list. GNU C17 (Ubuntu 12-20220222-1ubuntu1) version 12.0.1 20220222 (experimental) [master r12-7325-g2f59f067610] (x86_64-linux-gnu) compiled by GNU C version 12.0.1 20220222 (experimental) [master r12-7325-g2f59f067610], GMP version 6.2.1, MPFR version 4.1.0, MPC version 1.2.1, isl version isl-0.24-GMP GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072 Compiler executable checksum: b0de683ccdd6a31c725d9273cea9e1f8 COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/12/:/usr/lib/gcc/x86_64-linux-gnu/12/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/12/:/usr/lib/gcc/x86_64-linux-gnu/ LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/12/:/usr/lib/gcc/x86_64-linux-gnu/12/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/12/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/12/../../../:/lib/:/usr/lib/ COLLECT_GCC_OPTIONS='-O1' '-S' '-v' '-mtune=generic' '-march=x86-64' ``` The gcc is installed by apt on ubuntu 22.04. If I change the `while (1){}` to `return ;` then the code will be right. Or change the `+2` of `(volatile size_t *)(0xb8000+160*24)+2` to `+1` or `+0`.