Re: [patch,loopiv] misaligned packed array memory access

[Christian BRUEL <christian dot bruel at st dot com>]

Adding a testcase to the patch for the testsuite.

(aborts on sh-superh-elf-gcc),

Regards

-c

2008-01-28  Christian Bruel  <christian.bruel@st.com

	* gcc.dg/packed-array.c: New testcase.


Christian BRUEL wrote:
> The attached test case reduces a misaligned field access from an array 
> of packed structs. In this example compiled with -O2 the field 
> wMaxPacketSize is accessed (on sh4) with a mov.w instruction although it 
> is byte aligned.
>
> The tree-ssa-loop ivopts did not check packed struct offsets indexed by 
> an induction variable. Thus if the struct size is not aligned, the field 
>  becomes unaligned after the first iteration even if it was aligned from 
> the base of this structure.
>
> This patch solves this problem by expanding may_be_unaligned_p to check 
> that a loop carried offset is a multiple of the desired alignment.
>
> This bug impacted STRICT_ALIGNMENT targets. I regtested on sh-superh-elf 
> and sh4-linux-gnu.
>
> Also bootstraped for i686-pc-linux-gnu.
>
> Thanks you for any feedback and trunk approval if ok.
>
> -c
>
> 2008-01-28  Christian Bruel  <christian.bruel@st.com>
>
>     * tree-ssa-loop-ivopts.c (may_be_unaligned_p): check loop carried 
> offset.
>     * (loop_offset_multiple_of): new function.

/* { dg-do run } */
/* { dg-options "-O2 -fno-inline" } */

struct usb_interface_descriptor {
 unsigned short wMaxPacketSize;
  char e;
} __attribute__ ((packed));

struct usb_device {
 int devnum;
 struct usb_interface_descriptor if_desc[2];
};

extern int printf (const char *, ...);

void foo (unsigned short a)
{
  printf ("%d\n", a);
}

struct usb_device ndev;

void usb_set_maxpacket(int n)
{
  int i;

  for(i=0; i<n;i++)
    foo((&ndev)->if_desc[i].wMaxPacketSize);
}

int
main()
{
  usb_set_maxpacket(2);
  return 0;
}