[PATCH] Fix PR tree-optimization/53636 (SLP generates invalid misaligned access)
Mikael Pettersson
mikpe@it.uu.se
Wed Jun 20 12:05:00 GMT 2012
Richard Guenther writes:
> On Tue, Jun 19, 2012 at 11:36 PM, Mikael Pettersson <mikpe@it.uu.se> wrote:
> > Richard Guenther writes:
> > > On Fri, Jun 15, 2012 at 5:00 PM, Ulrich Weigand <uweigand@de.ibm.com> wrote:
> > > > Richard Guenther wrote:
> > > >> On Fri, Jun 15, 2012 at 3:13 PM, Ulrich Weigand <uweigand@de.ibm.com> wrote:
> > > >> > However, there is a second case where we need to check every pass: if
> > > >> > we're not actually vectorizing any loop, but are performing basic-block
> > > >> > SLP. In this case, it would appear that we need the same check as
> > > >> > described in the comment above, i.e. to verify that the stride is a
> > > >> > multiple of the vector size.
> > > >> >
> > > >> > The patch below adds this check, and this indeed fixes the invalid access
> > > >> > I was seeing in the test case (in the final assembler, we now get a
> > > >> > vld1.16 instead of vldr).
> > > >> >
> > > >> > Tested on arm-linux-gnueabi with no regressions.
> > > >> >
> > > >> > OK for mainline?
> > > >>
> > > >> Ok.
> > > >
> > > > Thanks for the quick review; I've checked this in to mainline now.
> > > >
> > > > I just noticed that the test case also crashes on 4.7, but not on 4.6.
> > > >
> > > > Would a backport to 4.7 also be OK, once testing passes?
> > >
> > > Yes. Please leave it on mainline a few days to catch fallout from
> > > autotesters.
> >
> > This patch caused
> >
> > FAIL: gcc.dg/vect/bb-slp-16.c scan-tree-dump-times slp "basic block vectorized using SLP" 1
> >
> > on sparc64-linux. Comparing the pre and post patch dumps for that file shows
> >
> > 22: vect_compute_data_ref_alignment:
> > 22: misalign = 4 bytes of ref MEM[(unsigned int *)pout_90 + 28B]
> > 22: vect_compute_data_ref_alignment:
> > -22: force alignment of arr[i_87]
> > -22: misalign = 0 bytes of ref arr[i_87]
> > +22: SLP: step doesn't divide the vector-size.
> > +22: Unknown alignment for access: arr
> >
> > (lots of stuff that's simply gone)
> >
> > -22: BASIC BLOCK VECTORIZED
> > -
> > -22: basic block vectorized using SLP
> > +22: not vectorized: unsupported unaligned store.arr[i_87]
> > +22: not vectorized: unsupported alignment in basic block.
>
> In this testcase the alignment of arr[i] should be irrelevant - it is
> not part of
> the stmts that are going to be vectorized. But of course this may be
> simply an odering issue in how we analyze data-references / statements
> in basic-block vectorization (thus we possibly did not yet declare the
> arr[i] = i statement as not taking part in the vectorization).
>
> The line
>
> > -22: force alignment of arr[i_87]
>
> is odd, too - as said we do not need to touch arr when vectorizing the
> basic-block.
>
> Ulrich, can you look into this or do you want me to take a look here?
>
> Mikael - please open a bugreport for this.
I opened PR53729 for this, with an update saying that powerpc64-linux
also has this regression.
/Mikael
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