[PATCH][vect] Disable vectorization of epilogues for loops with SIMDUID set

["Andre Vieira (lists)" <andre dot simoesdiasvieira at arm dot com>]

Hi,

I was using loop->simdlen to detect whether it was a SIMD loop and I 
don't believe that was correct, as can be witnessed by the mass failures 
in libgomp. My apologies for not running this, didn't think of it!

I found that these were failing because we do not handle vectorization 
of epilogues correctly when SIMDUID is set. For now Jakub and I agreed 
to disable epilogue vectorization for loops where SIMDUID is set until 
we have fixed this. See further comments inline.

I bootstrapped it on aarch64 and x86_64, ran libgomp on both.

This OK for trunk?

Cheers,
Andre

gcc/ChangeLog:
2019-11-04  Andre Vieira  <andre.simoesdiasvieira@arm.com>

        * tree-vect-loop.c (vect_analyze_loop): Disable epilogue
        vectorization if loop->simduid is non null.

On 31/10/2019 16:58, Jakub Jelinek wrote:

> FAIL: libgomp.c/../libgomp.c-c++-common/loop-1.c execution test
> FAIL: libgomp.c/examples-4/simd-3.c execution test
> FAIL: libgomp.c/pr58392.c execution test
> FAIL: libgomp.c/scan-13.c execution test
> FAIL: libgomp.c/scan-17.c execution test
> FAIL: libgomp.c/scan-19.c execution test
> FAIL: libgomp.c/scan-20.c execution test
> FAIL: libgomp.c/simd-10.c execution test
> FAIL: libgomp.c/simd-12.c execution test
> FAIL: libgomp.c/simd-13.c execution test
> FAIL: libgomp.c/simd-6.c execution test
> FAIL: libgomp.c++/../libgomp.c-c++-common/loop-1.c execution test
> FAIL: libgomp.c++/simd-8.C execution test
> FAIL: libgomp.fortran/examples-4/simd-3.f90   -O1  execution test
> FAIL: libgomp.fortran/examples-4/simd-3.f90   -O2  execution test
> FAIL: libgomp.fortran/examples-4/simd-3.f90   -O3 -fomit-frame-pointer -funroll-loops -fpeel-loops -ftracer -finline-functions  execution test
> FAIL: libgomp.fortran/examples-4/simd-3.f90   -O3 -g  execution test
> FAIL: libgomp.fortran/examples-4/simd-3.f90   -Os  execution test
> FAIL: libgomp.fortran/nestedfn5.f90   -O1  execution test
> FAIL: libgomp.fortran/nestedfn5.f90   -O2  execution test
> FAIL: libgomp.fortran/nestedfn5.f90   -O3 -fomit-frame-pointer -funroll-loops -fpeel-loops -ftracer -finline-functions  execution test
> FAIL: libgomp.fortran/nestedfn5.f90   -O3 -g  execution test
> FAIL: libgomp.fortran/nestedfn5.f90   -Os  execution test

These should go away now, but we should revisit SIMDUID and epilogue 
vectorization later.  I tried to look into it, but I am afraid I know 
very little about SIMD loops to figure out how to make this work.
> On i686-linux, I also see newly
> FAIL: gcc.dg/vect/vect-epilogues.c -flto -ffat-lto-objects  scan-tree-dump vect "LOOP EPILOGUE VECTORIZED"
> FAIL: gcc.dg/vect/vect-epilogues.c scan-tree-dump vect "LOOP EPILOGUE VECTORIZED"
> and in libgomp just

These, just like for arm should be skipped for i686, I suspect it 
doesn't know how to vectorize for lower VF's.  Could someone add the 
appropriate skip target triple for i686?

> FAIL: libgomp.c/examples-4/simd-3.c execution test
> FAIL: libgomp.c/scan-13.c execution test
> FAIL: libgomp.c/scan-17.c execution test
> FAIL: libgomp.fortran/examples-4/simd-3.f90   -O1  execution test
> FAIL: libgomp.fortran/examples-4/simd-3.f90   -O2  execution test
> FAIL: libgomp.fortran/examples-4/simd-3.f90   -O3 -fomit-frame-pointer -funroll-loops -fpeel-loops -ftracer -finline-functions  execution test
> FAIL: libgomp.fortran/examples-4/simd-3.f90   -O3 -g  execution test
> FAIL: libgomp.fortran/examples-4/simd-3.f90   -Os  execution test

Same as the other libgomp tests. Should go away now.

diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
index fa873e9b435037e5a81dda6615cab809d2d4de48..d3a0fa015332dbcccf84bc68531dc1e49550cc19 100644
--- a/gcc/tree-vect-loop.c
+++ b/gcc/tree-vect-loop.c
@@ -2383,10 +2383,11 @@ vect_analyze_loop (class loop *loop, loop_vec_info orig_loop_vinfo,
   poly_uint64 lowest_th = 0;
   unsigned vectorized_loops = 0;
 
-  /* Only vectorize epilogues if PARAM_VECT_EPILOGUES_NOMASK is enabled, this
-     is not a simd loop and it is the most inner loop.  */
+  /* Only vectorize epilogues if PARAM_VECT_EPILOGUES_NOMASK is enabled,
+     SIMDLEN is not set, SIMDUID is not set and this is the most inner loop.
+     TODO: Enable epilogue vectorization for loops with SIMDUID set.  */
   bool vect_epilogues
-    = !loop->simdlen && loop->inner == NULL
+    = loop->simdlen == 0 && loop->simduid == NULL_TREE && loop->inner == NULL
       && PARAM_VALUE (PARAM_VECT_EPILOGUES_NOMASK);
   while (1)
     {