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From: "vries at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/97338] New: [nvptx] Convergence checking
Date: Thu, 08 Oct 2020 16:14:18 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D97338

            Bug ID: 97338
           Summary: [nvptx] Convergence checking
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

With ptx, we have insns that need to be executed in convergent mode, that i=
s,
all threads in the warp active.

We can unfortunately not enforce this, but we could check it, which could h=
elp
pinpoint problems.

A ptx insn:
...
  vote.ballot.b32 %rbla, 1;
...
gives us the regmask of active threads, so we could check:
...
{
  .reg .u32 %rwarp_active_mask;
  vote.ballot.b32 %rwarp_active_mask, 1;
  .reg .pred %pconvergent;
  setp.eq.u32 %pconvergent,%rwarp_active_mask,-1;
  @ ! %pconvergent trap;
}
...=