[Bug target/47133] New: code size opportunity for boolean expression evaluation

[carrot at google dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47133

           Summary: code size opportunity for boolean expression
                    evaluation
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: car...@google.com
            Target: arm-eabi


Compile the following code with options -march=armv7-a -mthumb -Os

struct S
{
  int f1, f2;
};

int t04(int x, struct S* p)
{
  return p->f1 == 9 && p->f2 == 0;
}

GCC 4.6 generates:

t04:
    ldr    r3, [r1, #0]
    cmp    r3, #9             // A
    bne    .L3
    ldr    r0, [r1, #4]
    rsbs    r0, r0, #1
    it    cc
    movcc    r0, #0
    bx    lr                 // C
.L3:
    movs    r0, #0             // B
    bx    lr


Instruction B can be moved before instruction A, and instruction C can be
removed. 

t04:
    ldr    r3, [r1, #0]
        movs    r0, #0
    cmp    r3, #9            
    bne    .L3
    ldr    r0, [r1, #4]
    rsbs    r0, r0, #1
    it    cc
    movcc    r0, #0
.L3:
    bx    lr

When compiled to arm instructions, it has the same problem.

It should be enabled for code size optimization only because it may execute one
more instruction run time.

Looks like an if-conversion opportunity.