https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64992
Bug ID: 64992 Summary: More optimize opportunity Product: gcc Version: 5.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: tree-optimization Assignee: unassigned at gcc dot gnu.org Reporter: ishiura-compiler at ml dot kwansei.ac.jp The two programs (A.c) and (B.c) only differ by one line (marked by "// <---HERE"), where (B.c) simply replace local variable b by its initial value 2U. The code (A.s) for (A.c) is less optimized than (B.s) for (B.c). (org.c) int main (void) { volatile int a = -1; unsigned int b = 2U; int c = a + 0; unsigned d = b * (1 == c); //<---HERE if (c == -1) ; else __builtin_abort(); if (d == 0U) ; else __builtin_abort(); return 0; } (opt.c) int main (void) { volatile int a = -1; unsigned int b = 2U; int c = a + 0; unsigned d = 2U * (1 == c); //<---HERE if (c == -1) ; else __builtin_abort(); if (d == 0U) ; else __builtin_abort(); return 0; } (org.s) main: .LFB0: .cfi_startproc subq $24, %rsp .cfi_def_cfa_offset 32 xorl %eax, %eax movl $-1, 12(%rsp) movl 12(%rsp), %edx cmpl $1, %edx sete %al addl %eax, %eax cmpl $-1, %edx jne .L3 testl %eax, %eax jne .L3 addq $24, %rsp .cfi_remember_state .cfi_def_cfa_offset 8 ret .L3: .cfi_restore_state call abort .cfi_endproc .LFE0: .size main, .-main .section .text.unlikely .LCOLDE0: .section .text.startup .LHOTE0: .ident "GCC: (GNU) 5.0.0 20150205 (experimental)" .section .note.GNU-stack,"",@progbits (opt.s) main: .LFB0: .cfi_startproc subq $24, %rsp .cfi_def_cfa_offset 32 movl $-1, 12(%rsp) movl 12(%rsp), %eax cmpl $-1, %eax jne .L5 xorl %eax, %eax addq $24, %rsp .cfi_remember_state .cfi_def_cfa_offset 8 ret .L5: .cfi_restore_state call abort .cfi_endproc .LFE0: .size main, .-main .section .text.unlikely .LCOLDE0: .section .text.startup .LHOTE0: .ident "GCC: (GNU) 5.0.0 20150205 (experimental)" .section .note.GNU-stack,"",@progbits $ x86_64-unknown-linux-gnu-gcc-5.0.0 -v Using built-in specs. COLLECT_GCC=x86_64-unknown-linux-gnu-gcc-5.0.0 COLLECT_LTO_WRAPPER=/usr/local/x86_64-tools/gcc-5.0.0/libexec/gcc/x86_64-unknown-linux-gnu/5.0.0/lto-wrapper Target: x86_64-unknown-linux-gnu Configured with: /home/iwatsuji/gcc/configure --prefix=/usr/local/x86_64-tools/gcc-5.0.0/ --with-gmp=/usr/local/gmp-5.1.1/ --with-mpfr=/usr/local/mpfr-3.1.2/ --with-mpc=/usr/local/mpc-1.0.1/ --disable-multilib --disable-nls --enable-languages=c Thread model: posix gcc version 5.0.0 20150205 (experimental) (GCC)