[Bug web/43473] New: hword size destination variable induces suboptimal code generation compared to full word size var

[mirq-gccboogs at rere dot qmqm dot pl]

unsigned short a;
unsigned b;
#define d 0xC000

void ma()
{
        unsigned short u = (d >> 1) & 0x55555555;

        a = (a & ~u) | d;
}

void mb()
{
        unsigned short u = (d >> 1) & 0x55555555;

        b = (b & ~u) | d;
}

generates:
ma:
        ldr     r3, .L2
        ldrh    r2, [r3, #0]
        mvn     r2, r2, asl #18
        mvn     r2, r2, lsr #18
        strh    r2, [r3, #0]    @ movhi
        bx      lr
.L2:
        .word   a

mb:
        ldr     r3, .L5
        ldr     r2, [r3, #0]
        orr     r2, r2, #49152
        str     r2, [r3, #0]
        bx      lr
.L5:
        .word   b

This is with -O. Without optimization it looks even worse:

(gcc 4.5 svn 157582)

Code without -O looks even worse:

        mov     r3, #16384
        strh    r3, [fp, #-6]   @ movhi
        ldrh    r3, [fp, #-6]
        mvn     r3, r3
        mov     r3, r3, asl #16
        mov     r2, r3, lsr #16
        ldr     r3, .L2
        ldrh    r3, [r3, #0]
        mov     r3, r3, asl #16
        mov     r3, r3, lsr #16
        and     r3, r2, r3
        mov     r3, r3, asl #16
        mov     r3, r3, lsr #16
        mvn     r3, r3, asl #18
        mvn     r3, r3, lsr #18
        mov     r3, r3, asl #16
        mov     r3, r3, lsr #16
        mov     r3, r3, asl #16
        mov     r2, r3, lsr #16
        ldr     r3, .L2
        strh    r2, [r3, #0]    @ movhi

compared to:

        mov     r3, #16384
        strh    r3, [fp, #-6]   @ movhi
        ldrh    r3, [fp, #-6]
        mvn     r3, r3
        mov     r2, r3
        ldr     r3, .L5
        ldr     r3, [r3, #0]
        and     r3, r2, r3
        orr     r2, r3, #49152
        ldr     r3, .L5
        str     r2, [r3, #0]


-- 
           Summary: hword size destination variable induces suboptimal code
                    generation compared to full word size var
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: web
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: mirq-gccboogs at rere dot qmqm dot pl
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: arm-none-eabi


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43473