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From: "tschwinge at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/107344] New: GCC/nvptx SESE region optimization
Date: Fri, 21 Oct 2022 09:24:39 +0000
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: 13.0
X-Bugzilla-Keywords: openacc
X-Bugzilla-Severity: normal
X-Bugzilla-Who: tschwinge at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107344

            Bug ID: 107344
           Summary: GCC/nvptx SESE region optimization
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Keywords: openacc
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tschwinge at gcc dot gnu.org
                CC: vries at gcc dot gnu.org
  Target Milestone: ---
            Target: nvptx

GCC/nvptx has a "SESE region optimization",
<https://inbox.sourceware.org/gcc-patches/564CC75D.3020309@acm.org>.

A "regression" has been introduced by recent commit
r13-3217-gc4d15dddf6b9eacb36f535807ad2ee364af46e04 "[PR107195] Set range to
zero when nonzero mask is 0":

    UNSUPPORTED: libgomp.oacc-c/../libgomp.oacc-c-c++-common/nvptx-sese-1.c
-DACC_DEVICE_TYPE_nvidia=3D1 -DACC_MEM_SHARED=3D0 -foffload=3Dnvptx-none  -=
O0=20
    PASS: libgomp.oacc-c/../libgomp.oacc-c-c++-common/nvptx-sese-1.c
-DACC_DEVICE_TYPE_nvidia=3D1 -DACC_MEM_SHARED=3D0 -foffload=3Dnvptx-none  -=
O2  (test
for excess errors)
    PASS: libgomp.oacc-c/../libgomp.oacc-c-c++-common/nvptx-sese-1.c
-DACC_DEVICE_TYPE_nvidia=3D1 -DACC_MEM_SHARED=3D0 -foffload=3Dnvptx-none  -=
O2=20
execution test
    [-PASS:-]{+FAIL:+}
libgomp.oacc-c/../libgomp.oacc-c-c++-common/nvptx-sese-1.c
-DACC_DEVICE_TYPE_nvidia=3D1 -DACC_MEM_SHARED=3D0 -foffload=3Dnvptx-none  -=
O2=20=20
scan-nvptx-none-offload-rtl-dump mach "SESE regions:.*
[0-9]+{[0-9]+->[0-9]+(\\.[0-9]+)+}"

Same for C++.

During investigation of that issue (which I suppose is just one random
example), I found that earlier code transformations/optimizations may inhib=
it
this "Neuter whole SESE regions" optimization.

It's unclear to me if this is an actual "problem", which optimization is "m=
ore
important".=