[Bug tree-optimization/53870] New: Redundant memory load

[unixoid2003 at mail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53870

             Bug #: 53870
           Summary: Redundant memory load
    Classification: Unclassified
           Product: gcc
           Version: 4.7.1
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: unixoid2...@mail.ru


class test{
public:
    void remove();
private:
    test *next;
    test *prev;
};

void test::remove(){
    next->prev=prev;
    prev->next=next;
}

arm-none-eabi-gcc++ -mcpu=cortex-m3 -mthumb -O2

00000000 <_ZN4test6removeEv>:
   0:    6803          ldr    r3, [r0, #0]
   2:    6842          ldr    r2, [r0, #4]
   4:    605a          str    r2, [r3, #4]
   6:    6842          ldr    r2, [r0, #4]   ; Redundant
   8:    6013          str    r3, [r2, #0]
   a:    4770          bx    lr

But this code compiles better:

void test::remove(){
    test *n=next,*p=prev;
    n->prev=p;
    p->next=n;
}

00000000 <_ZN4test6removeEv>:
   0:    e890 000c     ldmia.w    r0, {r2, r3}
   4:    6053          str    r3, [r2, #4]
   6:    601a          str    r2, [r3, #0]
   8:    4770          bx    lr