Poor code for alloca

[Yao Qi]

#include <alloca.h>
extern void bar(void *);

int foo(int i)
{
  bar(alloca(i));
  return 0;
}
$ arm-none-linux-gnueabi-gcc --version
arm-none-linux-gnueabi-gcc (GCC) 4.6.0 20100907 (experimental)
$arm-none-linux-gnueabi-gcc -march=armv7-a -O2 -S poor_alloca.c

FSF GCC trunk generate codes:

foo:
        @ args = 0, pretend = 0, frame = 0
        @ frame_needed = 1, uses_anonymous_args = 0
        add r0, r0, #14
        bic r0, r0, #7
        stmfd sp!, {fp, lr}
        add fp, sp, #4
        sub sp, sp, r0
        mov r0, sp
        bl bar
        mov r0, #0
        sub sp, fp, #4
        ldmfd sp!, {fp, pc}

The instructions for alignment are not necessary.

[CodeSourcery #1675]

[Yao Qi (yao-codesourcery)]

Code size will be reduced once this bug is fixed.

[Yao Qi (yao-codesourcery)]

Please ignore my comment #1, and sentence "The instructions for alignment are not necessary." in bug report.

After talk with cltang, we realize that alignment is necessary here. However, 'add r0, r0, #14' can be changed to 'add r0, r0, #7'.