Restore 'libgomp.oacc-c-c++-common/nvptx-sese-1.c' SESE regions checking [PR107195, PR107344] (was: [COMMITTED] [PR107195] Set range to zero when nonzero mask is 0.)

[Thomas Schwinge <thomas@codesourcery.com>]

Hi!

On 2022-10-17T09:43:37+0200, I wrote:
> On 2022-10-11T10:31:37+0200, Aldy Hernandez via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
>> When solving 0 = _15 & 1, we calculate _15 as:
>>
>>      [irange] int [-INF, -2][0, +INF] NONZERO 0xfffffffe
>>
>> The known value of _15 is [0, 1] NONZERO 0x1 which is intersected with
>> the above, yielding:
>>
>>      [0, 1] NONZERO 0x0
>>
>> This eventually gets copied to a _Bool [0, 1] NONZERO 0x0.
>>
>> This is problematic because here we have a bool which is zero, but
>> returns false for irange::zero_p, since the latter does not look at
>> nonzero bits.  This causes logical_combine to assume the range is
>> not-zero, and all hell breaks loose.
>>
>> I think we should just normalize a nonzero mask of 0 to [0, 0] at
>> creation, thus avoiding all this.
>
> 1. This commit r13-3217-gc4d15dddf6b9eacb36f535807ad2ee364af46e04
> "[PR107195] Set range to zero when nonzero mask is 0" broke a GCC/nvptx
> offloading test case:
>
>     UNSUPPORTED: libgomp.oacc-c/../libgomp.oacc-c-c++-common/nvptx-sese-1.c -DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0 -foffload=nvptx-none  -O0
>     PASS: libgomp.oacc-c/../libgomp.oacc-c-c++-common/nvptx-sese-1.c -DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0 -foffload=nvptx-none  -O2  (test for excess errors)
>     PASS: libgomp.oacc-c/../libgomp.oacc-c-c++-common/nvptx-sese-1.c -DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0 -foffload=nvptx-none  -O2  execution test
>     [-PASS:-]{+FAIL:+} libgomp.oacc-c/../libgomp.oacc-c-c++-common/nvptx-sese-1.c -DACC_DEVICE_TYPE_nvidia=1 -DACC_MEM_SHARED=0 -foffload=nvptx-none  -O2   scan-nvptx-none-offload-rtl-dump mach "SESE regions:.* [0-9]+{[0-9]+->[0-9]+(\\.[0-9]+)+}"
>
> Same for C++.
>
> I'll later send a patch (for the test case!) to fix that up.

Pushed to master branch commit a9de836c2b22f878cff592b96e11c1b95d4d36ee
"Restore 'libgomp.oacc-c-c++-common/nvptx-sese-1.c' SESE regions checking [PR107195, PR107344]",
see attached.

That discussion I suppose is to be continued in
<https://gcc.gnu.org/PR107344> "GCC/nvptx SESE region optimization".


Grüße
 Thomas


>>      PR tree-optimization/107195
>>
>> gcc/ChangeLog:
>>
>>      * value-range.cc (irange::set_range_from_nonzero_bits): Set range
>>      to [0,0] when nonzero mask is 0.
>>
>> gcc/testsuite/ChangeLog:
>>
>>      * gcc.dg/tree-ssa/pr107195-1.c: New test.
>>      * gcc.dg/tree-ssa/pr107195-2.c: New test.
>> ---
>>  gcc/testsuite/gcc.dg/tree-ssa/pr107195-1.c | 15 +++++++++++++++
>>  gcc/testsuite/gcc.dg/tree-ssa/pr107195-2.c | 16 ++++++++++++++++
>>  gcc/value-range.cc                         |  5 +++++
>>  3 files changed, 36 insertions(+)
>>  create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr107195-1.c
>>  create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr107195-2.c
>>
>> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr107195-1.c b/gcc/testsuite/gcc.dg/tree-ssa/pr107195-1.c
>> new file mode 100644
>> index 00000000000..a0c20dbd4b1
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr107195-1.c
>> @@ -0,0 +1,15 @@
>> +// { dg-do run }
>> +// { dg-options "-O1 -fno-tree-ccp" }
>> +
>> +int a, b;
>> +int main() {
>> +  int c = 0;
>> +  if (a)
>> +    c = 1;
>> +  c = 1 & (a && c) && b;
>> +  if (a) {
>> +    b = c;
>> +    __builtin_abort ();
>> +  }
>> +  return 0;
>> +}
>> diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr107195-2.c b/gcc/testsuite/gcc.dg/tree-ssa/pr107195-2.c
>> new file mode 100644
>> index 00000000000..d447c78bdd3
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/tree-ssa/pr107195-2.c
>> @@ -0,0 +1,16 @@
>> +// { dg-do run }
>> +// { dg-options "-O1" }
>> +
>> +int a, b;
>> +int main() {
>> +  int c = 0;
>> +  long d;
>> +  for (; b < 1; b++) {
>> +    (c && d) & 3 || a;
>> +    d = c;
>> +    c = -1;
>> +    if (d)
>> +      __builtin_abort();
>> +  }
>> +  return 0;
>> +}
>> diff --git a/gcc/value-range.cc b/gcc/value-range.cc
>> index a14f9bc4394..e07d2aa9a5b 100644
>> --- a/gcc/value-range.cc
>> +++ b/gcc/value-range.cc
>> @@ -2903,6 +2903,11 @@ irange::set_range_from_nonzero_bits ()
>>      }
>>        return true;
>>      }
>> +  else if (popcount == 0)
>> +    {
>> +      set_zero (type ());
>> +      return true;
>> +    }
>>    return false;
>>  }
>>
>> --
>> 2.37.3
>
>
> From dc4644dcef05a1f21a9ebc194689f31412811387 Mon Sep 17 00:00:00 2001
> From: Thomas Schwinge <thomas@codesourcery.com>
> Date: Mon, 17 Oct 2022 09:10:03 +0200
> Subject: [PATCH] Add 'c-c++-common/torture/pr107195-1.c' [PR107195]
>
> ... to display optimization performed as of recent
> commit r13-3217-gc4d15dddf6b9eacb36f535807ad2ee364af46e04
> "[PR107195] Set range to zero when nonzero mask is 0".
>
>       PR tree-optimization/107195
>       gcc/testsuite/
>       * c-c++-common/torture/pr107195-1.c: New.
> ---
>  .../c-c++-common/torture/pr107195-1.c         | 41 +++++++++++++++++++
>  1 file changed, 41 insertions(+)
>  create mode 100644 gcc/testsuite/c-c++-common/torture/pr107195-1.c
>
> diff --git a/gcc/testsuite/c-c++-common/torture/pr107195-1.c b/gcc/testsuite/c-c++-common/torture/pr107195-1.c
> new file mode 100644
> index 000000000000..1e201c1f5e6c
> --- /dev/null
> +++ b/gcc/testsuite/c-c++-common/torture/pr107195-1.c
> @@ -0,0 +1,41 @@
> +/* Inspired by 'libgomp.oacc-c-c++-common/nvptx-sese-1.c'.  */
> +
> +/* { dg-additional-options -fdump-tree-optimized-raw }
> +   { dg-skip-if {} { *-*-* } { {-flto -fno-fat-lto-objects} } { } } */
> +
> +#if 1
> +extern int
> +__attribute__((const))
> +foo (int);
> +#else
> +int
> +__attribute__((noinline))
> +foo (int x)
> +{
> +  return x & 2;
> +}
> +#endif
> +
> +int f (int r)
> +{
> +  if (foo (r)) /* If this first 'if' holds...  */
> +    r *= 2;  /* ..., 'r' now has a zero-value lower-most bit...  */
> +
> +  if (r & 1) /* ..., so this second 'if' can never hold...  */
> +    { /* ..., so this is unreachable.  */
> +#if 1
> +      /* In constrast, if the first 'if' does not hold ('foo (r) == 0'), the
> +      second 'if' may hold, but we know ('foo' being 'const') that
> +      'foo (r) == 0', so don't have to re-evaluate it here: */
> +      r += foo (r);
> +      /* Thus, if optimizing, we only ever expect one call of 'foo'.
> +      { dg-final { scan-tree-dump-times {gimple_call <foo,} 1 optimized { target __OPTIMIZE__ } } }
> +      { dg-final { scan-tree-dump-times {gimple_call <foo,} 2 optimized { target { ! __OPTIMIZE__ } } } }
> +      */
> +#else
> +      r += foo (-r);
> +#endif
> +    }
> +
> +  return r;
> +}
> --
> 2.35.1
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