[Bug target/42879] New: Replace "tst r3, 1" with "lsl r3, r3, 31" in thumb2

["carrot at google dot com" <gcc-bugzilla at gcc dot gnu dot org>]

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

struct A
{
  bool v:1;
};

bool bar();

bool foo(struct A* p)
{
  if (p->v)
    return true;
  return bar();
}

Gcc generates

_Z3fooP1A:
        push    {r3, lr}
        .save {r3, lr}
.LCFI0:
        ldrb    r3, [r0, #0]    @ zero_extendqisi2
        tst     r3, #1
        bne     .L3
        bl      _Z3barv
        b       .L2
.L3:
        movs    r0, #1
.L2:
        pop     {r3, pc}

The "tst  r3, #1" is a 32 bit instruction, it can be replaced by a 16 bit
instruction "lsl r3, r3, 31" while still retain the original semantics.


-- 
           Summary: Replace "tst  r3, 1" with "lsl r3, r3, 31" in thumb2
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: carrot at google dot com
 GCC build triplet: i686-linux
  GCC host triplet: i686-linux
GCC target triplet: arm-eabi


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42879