[Bug rtl-optimization/109019] New: Failure to optimize b + c -1

[tkoenig at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109019

            Bug ID: 109019
           Summary: Failure to optimize b + c -1
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tkoenig at gcc dot gnu.org
  Target Milestone: ---

Looks like a general RTL issue, I see this on POWER, RV64 and ARM64 (the
latter two on godbolt).


[tkoenig@gcc135 ~]$ cat c.c
long foo (long b, long c)
{
  return b + c - 1;
}
[tkoenig@gcc135 ~]$ gcc -O3 -S c.c
[tkoenig@gcc135 ~]$ cat c.s
        .file   "c.c"
        .machine power8
        .abiversion 2
        .section        ".text"
        .align 2
        .p2align 4,,15
        .globl foo
        .type   foo, @function
foo:
.LFB0:
        .cfi_startproc
        add 3,3,4
        addi 3,3,-1
        blr
        .long 0
        .byte 0,0,0,0,0,0,0,0
        .cfi_endproc
.LFE0:
        .size   foo,.-foo
        .ident  "GCC: (GNU) 13.0.1 20230215 (experimental)"
        .section        .note.GNU-stack,"",@progbits

This should be

        addi    3,4,-1
        ret