[PATCH, 8/8] Do simple omp lowering for no address taken var

[Tom de Vries]

On 17-11-14 11:13, Richard Biener wrote:
> On Sat, 15 Nov 2014, Tom de Vries wrote:
>
>> >On 15-11-14 13:14, Tom de Vries wrote:
>>> > >Hi,
>>> > >
>>> > >I'm submitting a patch series with initial support for the oacc kernels
>>> > >directive.
>>> > >
>>> > >The patch series uses pass_parallelize_loops to implement parallelization of
>>> > >loops in the oacc kernels region.
>>> > >
>>> > >The patch series consists of these 8 patches:
>>> > >...
>>> > >      1  Expand oacc kernels after pass_build_ealias
>>> > >      2  Add pass_oacc_kernels
>>> > >      3  Add pass_ch_oacc_kernels to pass_oacc_kernels
>>> > >      4  Add pass_tree_loop_{init,done} to pass_oacc_kernels
>>> > >      5  Add pass_loop_im to pass_oacc_kernels
>>> > >      6  Add pass_ccp to pass_oacc_kernels
>>> > >      7  Add pass_parloops_oacc_kernels to pass_oacc_kernels
>>> > >      8  Do simple omp lowering for no address taken var
>>> > >...
>> >
>> >This patch lowers integer variables that do not have their address taken as
>> >local variable.  We use a copy at region entry and exit to copy the value in
>> >and out.
>> >
>> >In the context of reduction handling in a kernels region, this allows the
>> >parloops reduction analysis to recognize the reduction, even after oacc
>> >lowering has been done in pass_lower_omp.
>> >
>> >In more detail, without this patch, the omp_data_i load and stores are
>> >generated in place (in this case, in the loop):
>> >...
>> >                 {
>> >                   .omp_data_iD.2201 = &.omp_data_arr.15D.2220;
>> >                   {
>> >                     unsigned intD.9 iD.2146;
>> >
>> >                     iD.2146 = 0;
>> >                     goto <D.2207>;
>> >                     <D.2208>:
>> >                     D.2216 = .omp_data_iD.2201->cD.2203;
>> >                     c.9D.2176 = *D.2216;
>> >                     D.2177 = (long unsigned intD.10) iD.2146;
>> >                     D.2178 = D.2177 * 4;
>> >                     D.2179 = c.9D.2176 + D.2178;
>> >                     D.2180 = *D.2179;
>> >                     D.2217 = .omp_data_iD.2201->sumD.2205;
>> >                     D.2218 = *D.2217;
>> >                     D.2217 = .omp_data_iD.2201->sumD.2205;
>> >                     D.2219 = D.2180 + D.2218;
>> >                     *D.2217 = D.2219;
>> >                     iD.2146 = iD.2146 + 1;
>> >                     <D.2207>:
>> >                     if (iD.2146 <= 524287) goto <D.2208>; else goto <D.2209>;
>> >                     <D.2209>:
>> >                   }
>> >...
>> >
>> >With this patch, the omp_data_i load and stores for sum are generated at entry
>> >and exit:
>> >...
>> >                 {
>> >                   .omp_data_iD.2201 = &.omp_data_arr.15D.2218;
>> >                   D.2216 = .omp_data_iD.2201->sumD.2205;
>> >                   sumD.2206 = *D.2216;
>> >                   {
>> >                     unsigned intD.9 iD.2146;
>> >
>> >                     iD.2146 = 0;
>> >                     goto <D.2207>;
>> >                     <D.2208>:
>> >                     D.2217 = .omp_data_iD.2201->cD.2203;
>> >                     c.9D.2176 = *D.2217;
>> >                     D.2177 = (long unsigned intD.10) iD.2146;
>> >                     D.2178 = D.2177 * 4;
>> >                     D.2179 = c.9D.2176 + D.2178;
>> >                     D.2180 = *D.2179;
>> >                     sumD.2206 = D.2180 + sumD.2206;
>> >                     iD.2146 = iD.2146 + 1;
>> >                     <D.2207>:
>> >                     if (iD.2146 <= 524287) goto <D.2208>; else goto <D.2209>;
>> >                     <D.2209>:
>> >                   }
>> >                   *D.2216 = sumD.2206;
>> >                   #pragma omp return
>> >                 }
>> >...
>> >
>> >
>> >So, without the patch the reduction operation looks like this:
>> >...
>> >     *(.omp_data_iD.2201->sumD.2205) = *(.omp_data_iD.2201->sumD.2205) + x
>> >...
>> >
>> >And with this patch the reduction operation is simply:
>> >...
>> >     sumD.2206 = sumD.2206 + x:
>> >...
>> >
>> >OK for trunk?
> I presume the reason you are trying to do that here is that otherwise
> it happens too late?  What you do is what loop store motion would
> do.

Richard,

Thanks for the hint. I've built a reduction example:
...
void __attribute__((noinline))
f (unsigned int *__restrict__ a, unsigned int *__restrict__ sum, unsigned int n)
{
   unsigned int i;
   for (i = 0; i < n; ++i)
     *sum += a[i];
}...
and observed that store motion of the *sum store is done by pass_loop_im, 
provided the *sum load is taken out of the the loop by pass_pre first.

So alternatively, we could use pass_pre and pass_loop_im to achieve the same effect.

When trying out adding pass_pre as a part of the pass group pass_oacc_kernels, I 
found that also pass_copyprop was required to get parloops to recognize the 
reduction.

Attached patch adds the pre pass to pass group pass_oacc_kernels.

Bootstrapped and reg-tested in the same way as before.

OK for trunk?
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