[Beignet] [PATCH] GBE: handle dead loop BBs in liveness analysis.

[yan.wang at linux.intel.com]

I tried your patch and the bug is fixed.
Thanks.

Yan Wang

> LGTM, thanks.
>
>> -----Original Message-----
>> From: Gong, Zhigang
>> Sent: Friday, October 24, 2014 11:41
>> To: beignet at lists.freedesktop.org
>> Cc: yan.wang at linux.intel.com; Yang, Rong R; Gong, Zhigang
>> Subject: [PATCH] GBE: handle dead loop BBs in liveness analysis.
>>
>> Considering the following CFG, our previous liveness analysis will only
>> back
>> traverse from the exit point BB, thus the BB 6 and 7 will not be
>> handled.
>>
>>     4---
>>     |   |
>>     |   |
>>     5 --|---> 10 ---> ret
>>     |   |
>>     |   |
>>     6<--
>>     |
>>     |<--
>>     7   |
>>     |   |
>>      ---
>>
>> Although the CFG looks not a normal application as once it goes to block
>> 6, it
>> will enter a dead loop and will never return, we still need to compile
>> it
>> successfully.
>>
>> This patch is to fix the bug at:
>> https://bugs.freedesktop.org/show_bug.cgi?id=85362
>>
>> Signed-off-by: Zhigang Gong <zhigang.gong at intel.com>
>> ---
>>  backend/src/ir/liveness.cpp | 11 ++++++++++-
>> backend/src/ir/liveness.hpp
>> |  1 +
>>  2 files changed, 11 insertions(+), 1 deletion(-)
>>
>> diff --git a/backend/src/ir/liveness.cpp b/backend/src/ir/liveness.cpp
>> index
>> eaf6728..35b935f 100644
>> --- a/backend/src/ir/liveness.cpp
>> +++ b/backend/src/ir/liveness.cpp
>> @@ -41,7 +41,11 @@ namespace ir {
>>        }
>>      });
>>      // Now with iterative analysis, we compute liveout and livein sets
>> -    this->computeLiveInOut();
>> +    while (unvisitBlocks.size()) {
>> +      if (workSet.size() == 0)
>> +        workSet.insert(--unvisitBlocks.end(), unvisitBlocks.end());
>> +      this->computeLiveInOut();
>> +    }
>>      // extend register (def in loop, use out-of-loop) liveness to the
>> whole loop
>>      set<Register> extentRegs;
>>      this->computeExtraLiveInOut(extentRegs);
>> @@ -98,6 +102,7 @@ namespace ir {
>>        this->initInstruction(*info, insn);
>>      });
>>      liveness[&bb] = info;
>> +    unvisitBlocks.insert(info);
>>      if(!bb.liveout.empty())
>>        info->liveOut.insert(bb.liveout.begin(), bb.liveout.end());
>>    }
>> @@ -124,12 +129,16 @@ namespace ir {
>>      while(!workSet.empty()) {
>>        auto currInfo = *workSet.begin();
>>        workSet.erase(currInfo);
>> +      if (unvisitBlocks.find(currInfo) != unvisitBlocks.end())
>> +        unvisitBlocks.erase(currInfo);
>>        for (auto currOutVar : currInfo->liveOut)
>>          if (!currInfo->varKill.contains(currOutVar))
>>            currInfo->upwardUsed.insert(currOutVar);
>>        bool isChanged = false;
>>        for (auto prev : currInfo->bb.getPredecessorSet()) {
>>          BlockInfo *prevInfo = liveness[prev];
>> +        if (unvisitBlocks.find(currInfo) != unvisitBlocks.end())
>> +          unvisitBlocks.erase(currInfo);
>>          for (auto currInVar : currInfo->upwardUsed) {
>>            if (!prevInfo->bb.undefPhiRegs.contains(currInVar)) {
>>              auto changed = prevInfo->liveOut.insert(currInVar);
>> diff --git a/backend/src/ir/liveness.hpp b/backend/src/ir/liveness.hpp
>> index
>> d55e00d..d1e1a53 100644
>> --- a/backend/src/ir/liveness.hpp
>> +++ b/backend/src/ir/liveness.hpp
>> @@ -132,6 +132,7 @@ namespace ir {
>>      /*! Set of work list block which has exit(return) instruction */
>>      typedef set <struct BlockInfo*> WorkSet;
>>      WorkSet workSet;
>> +    WorkSet unvisitBlocks;
>>
>>      /*! Use custom allocators */
>>      GBE_CLASS(Liveness);
>> --
>> 1.8.3.2
>
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