> -----Original Message-----
> From: Bin.Cheng [mailto:amker.ch...@gmail.com]
> Sent: Monday, August 04, 2014 4:41 PM
> To: Zhenqiang Chen
> Cc: gcc-patches List
> Subject: Re: [PATCH, ivopt] Try aligned offset when get_address_cost
>
> On Mon, Aug 4, 2014 at 2:28 PM, Zhenqiang Chen
> <zhenqiang.c...@arm.com> wrote:
> > Hi,
> >
> > For some TARGET, like ARM THUMB1, the offset in load/store should be
> > nature aligned. But in function get_address_cost, when computing
> > max_offset, it only tries byte-aligned offsets:
> >
> > ((unsigned HOST_WIDE_INT) 1 << i) - 1
> >
> > which can not meet thumb_legitimate_offset_p check called from
> > thumb1_legitimate_address_p for HImode and SImode.
> >
> > The patch adds additional try for aligned offset:
> >
> > ((unsigned HOST_WIDE_INT) 1 << i) - GET_MODE_SIZE (address_mode).
> >
> > Bootstrap and no make check regression on X86-64.
> > No make check regression on qemu for Cortex-m0 and Cortex-m3.
> > For Cortex-m0, no performance changes with coremark and dhrystone.
> > Coremark code size is ~0.44 smaller. And eembcv2 code size is ~0.22
> > smaller. CSiBE code size is ~0.05% smaller.
> >
> > OK for trunk?
> >
> > Thanks!
> > -Zhenqiang
> >
> > ChangeLog
> > 2014-08-04 Zhenqiang Chen <zhenqiang.c...@arm.com>
> >
> > * tree-ssa-loop-ivopts.c (get_address_cost): Try aligned offset.
> >
> > testsuite/ChangeLog:
> > 2014-08-04 Zhenqiang Chen <zhenqiang.c...@arm.com>
> >
> > * gcc.target/arm/get_address_cost_aligned_max_offset.c: New
test.
> >
> > diff --git a/gcc/tree-ssa-loop-ivopts.c b/gcc/tree-ssa-loop-ivopts.c
> > index 3b4a6cd..562122a 100644
> > --- a/gcc/tree-ssa-loop-ivopts.c
> > +++ b/gcc/tree-ssa-loop-ivopts.c
> > @@ -3308,6 +3308,18 @@ get_address_cost (bool symbol_present, bool
> > var_present,
> > XEXP (addr, 1) = gen_int_mode (off, address_mode);
> > if (memory_address_addr_space_p (mem_mode, addr, as))
> > break;
> > + /* For some TARGET, like ARM THUMB1, the offset should be
nature
> > + aligned. Try an aligned offset if address_mode is not
QImode.
> > */
> > + off = (address_mode == QImode)
> > + ? 0
> > + : ((unsigned HOST_WIDE_INT) 1 << i)
> > + - GET_MODE_SIZE (address_mode);
> > + if (off > 0)
> > + {
> > + XEXP (addr, 1) = gen_int_mode (off, address_mode);
> > + if (memory_address_addr_space_p (mem_mode, addr, as))
> > + break;
> > + }
> Hi, Why not just check "address_mode != QImode"? Set off to 0 then check
it
> seems unnecessary.
Thanks for the comments.
((unsigned HOST_WIDE_INT) 1 << i) - GET_MODE_SIZE (address_mode) might be a
negative value except QImode. A negative value can not be max_offset. So we
do not need to check it.
For QImode, "((unsigned HOST_WIDE_INT) 1 << i) - GET_MODE_SIZE
(address_mode)" == "((unsigned HOST_WIDE_INT) 1 << i) - 1". It is already
checked. So no need to check it again.
I think the compiler can optimize the patch like
diff --git a/gcc/tree-ssa-loop-ivopts.c b/gcc/tree-ssa-loop-ivopts.c
index 3b4a6cd..213598a 100644
--- a/gcc/tree-ssa-loop-ivopts.c
+++ b/gcc/tree-ssa-loop-ivopts.c
@@ -3308,6 +3308,19 @@ get_address_cost (bool symbol_present, bool
var_present,
XEXP (addr, 1) = gen_int_mode (off, address_mode);
if (memory_address_addr_space_p (mem_mode, addr, as))
break;
+ /* For some TARGET, like ARM THUMB1, the offset should be nature
+ aligned. Try an aligned offset if address_mode is not QImode.
*/
+ if (address_mode != QImode)
+ {
+ off = ((unsigned HOST_WIDE_INT) 1 << i)
+ - GET_MODE_SIZE (address_mode);
+ if (off > 0)
+ {
+ XEXP (addr, 1) = gen_int_mode (off, address_mode);
+ if (memory_address_addr_space_p (mem_mode, addr, as))
+ break;
+ }
+ }
}
if (i == -1)
off = 0;
> Thanks,
> bin
> > }
> > if (i == -1)
> > off = 0;
> > diff --git
> > a/gcc/testsuite/gcc.target/arm/get_address_cost_aligned_max_offset.c
> > b/gcc/testsuite/gcc.target/arm/get_address_cost_aligned_max_offset.c
> > new file mode 100644
> > index 0000000..cc3e2f7
> > --- /dev/null
> > +++
> b/gcc/testsuite/gcc.target/arm/get_address_cost_aligned_max_offset
> > +++ .c
> > @@ -0,0 +1,28 @@
> > +/* { dg-do compile } */
> > +/* { dg-options "-mthumb -O2" } */
> > +/* { dg-require-effective-target arm_thumb1_ok } */
> > +
> > +unsigned int
> > +test (const short p16[6 * 64])
> > +{
> > + unsigned int i = 6;
> > + unsigned int ret = 0;
> > +
> > + do
> > + {
> > + unsigned long long *p64 = (unsigned long long*) p16;
> > + unsigned int *p32 = (unsigned int*) p16;
> > + ret += ret;
> > + if (p16[1] || p32[1])
> > + ret++;
> > + else if (p64[1] | p64[2] | p64[3])
> > + ret++;
> > + p16 += 64;
> > + i--;
> > + } while (i != 0);
> > +
> > + return ret;
> > +}
> > +
> > +/* { dg-final { scan-assembler-not "#22" } } */
> > +/* { dg-final { scan-assembler-not "#14" } } */
> >
> >
> >
