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Thu Sep 3 10:48:24 PDT 2015

Any suggestion?

On Wed, Sep 2, 2015 at 11:09 AM, Jonathan Roelofs via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

>
>
> On 9/2/15 12:07 PM, Mail Delivery System wrote:
>
> Forwarding to the new list...
>
>
>>
>> On 6/18/15 10:01 AM, Benjamin Kramer wrote:
>>
>>> Author: d0k
>>> Date: Thu Jun 18 11:01:00 2015
>>> New Revision: 240023
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=240023&view=rev
>>> Log:
>>> [EliminateDuplicatePHINodes] Replace custom hash map with DenseSet.
>>>
>>> While there use hash_combine instead of hand-rolled hashing. No
>>> functionality change intended.
>>>
>>
>> Something about this patch is causing a crash in the attached testcase
>> (which is already heavily reduced/redacted as much as I could). The
>> failure mode is an assertion fail in DenseMap:
>>
>> Assertion failed: (!FoundVal && "Key already in new map?"), function
>> moveFromOldBuckets, file
>> /Users/jroelofs/workdir/svn/llvm2/include/llvm/ADT/DenseMap.h, line 301.
>>
>> Unfortunately I can't get this to reproduce on trunk, and my stabs at
>> debugging it have been thus-far unsuccessful... Mind taking a look?
>>
>>
>> Thanks,
>>
>> Jon
>>
>>
>>> Modified:
>>>       llvm/trunk/lib/Transforms/Utils/Local.cpp
>>>
>>> Modified: llvm/trunk/lib/Transforms/Utils/Local.cpp
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/Local.cpp?rev=240023&r1=240022&r2=240023&view=diff
>>>
>>> ==============================================================================
>>> --- llvm/trunk/lib/Transforms/Utils/Local.cpp (original)
>>> +++ llvm/trunk/lib/Transforms/Utils/Local.cpp Thu Jun 18 11:01:00 2015
>>> @@ -14,6 +14,8 @@
>>>
>>>    #include "llvm/Transforms/Utils/Local.h"
>>>    #include "llvm/ADT/DenseMap.h"
>>> +#include "llvm/ADT/DenseSet.h"
>>> +#include "llvm/ADT/Hashing.h"
>>>    #include "llvm/ADT/STLExtras.h"
>>>    #include "llvm/ADT/SmallPtrSet.h"
>>>    #include "llvm/ADT/Statistic.h"
>>> @@ -828,64 +830,45 @@ bool llvm::TryToSimplifyUncondBranchFrom
>>>    /// orders them so it usually won't matter.
>>>    ///
>>>    bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
>>> -  bool Changed = false;
>>> -
>>>      // This implementation doesn't currently consider undef operands
>>>      // specially. Theoretically, two phis which are identical except for
>>>      // one having an undef where the other doesn't could be collapsed.
>>>
>>> -  // Map from PHI hash values to PHI nodes. If multiple PHIs have
>>> -  // the same hash value, the element is the first PHI in the
>>> -  // linked list in CollisionMap.
>>> -  DenseMap<uintptr_t, PHINode *> HashMap;
>>> +  struct PHIDenseMapInfo {
>>> +    static PHINode *getEmptyKey() {
>>> +      return DenseMapInfo<PHINode *>::getEmptyKey();
>>> +    }
>>> +    static PHINode *getTombstoneKey() {
>>> +      return DenseMapInfo<PHINode *>::getTombstoneKey();
>>> +    }
>>> +    static unsigned getHashValue(PHINode *PN) {
>>> +      // Compute a hash value on the operands. Instcombine will likely
>>> have
>>> +      // sorted them, which helps expose duplicates, but we have to
>>> check all
>>> +      // the operands to be safe in case instcombine hasn't run.
>>> +      return static_cast<unsigned>(hash_combine(
>>> +          hash_combine_range(PN->value_op_begin(), PN->value_op_end()),
>>> +          hash_combine_range(PN->block_begin(), PN->block_end())));
>>> +    }
>>> +    static bool isEqual(PHINode *LHS, PHINode *RHS) {
>>> +      if (LHS == getEmptyKey() || LHS == getTombstoneKey() ||
>>> +          RHS == getEmptyKey() || RHS == getTombstoneKey())
>>> +        return LHS == RHS;
>>> +      return LHS->isIdenticalTo(RHS);
>>> +    }
>>> +  };
>>>
>>> -  // Maintain linked lists of PHI nodes with common hash values.
>>> -  DenseMap<PHINode *, PHINode *> CollisionMap;
>>> +  // Set of unique PHINodes.
>>> +  DenseSet<PHINode *, PHIDenseMapInfo> PHISet;
>>>
>>>      // Examine each PHI.
>>> -  for (BasicBlock::iterator I = BB->begin();
>>> -       PHINode *PN = dyn_cast<PHINode>(I++); ) {
>>> -    // Compute a hash value on the operands. Instcombine will likely
>>> have sorted
>>> -    // them, which helps expose duplicates, but we have to check all the
>>> -    // operands to be safe in case instcombine hasn't run.
>>> -    uintptr_t Hash = 0;
>>> -    // This hash algorithm is quite weak as hash functions go, but it
>>> seems
>>> -    // to do a good enough job for this particular purpose, and is very
>>> quick.
>>> -    for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I !=
>>> E; ++I) {
>>> -      Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
>>> -      Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
>>> -    }
>>> -    for (PHINode::block_iterator I = PN->block_begin(), E =
>>> PN->block_end();
>>> -         I != E; ++I) {
>>> -      Hash ^= reinterpret_cast<uintptr_t>(static_cast<BasicBlock
>>> *>(*I));
>>> -      Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
>>> -    }
>>> -    // Avoid colliding with the DenseMap sentinels ~0 and ~0-1.
>>> -    Hash >>= 1;
>>> -    // If we've never seen this hash value before, it's a unique PHI.
>>> -    std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
>>> -      HashMap.insert(std::make_pair(Hash, PN));
>>> -    if (Pair.second) continue;
>>> -    // Otherwise it's either a duplicate or a hash collision.
>>> -    for (PHINode *OtherPN = Pair.first->second; ; ) {
>>> -      if (OtherPN->isIdenticalTo(PN)) {
>>> -        // A duplicate. Replace this PHI with its duplicate.
>>> -        PN->replaceAllUsesWith(OtherPN);
>>> -        PN->eraseFromParent();
>>> -        Changed = true;
>>> -        break;
>>> -      }
>>> -      // A non-duplicate hash collision.
>>> -      DenseMap<PHINode *, PHINode *>::iterator I =
>>> CollisionMap.find(OtherPN);
>>> -      if (I == CollisionMap.end()) {
>>> -        // Set this PHI to be the head of the linked list of colliding
>>> PHIs.
>>> -        PHINode *Old = Pair.first->second;
>>> -        Pair.first->second = PN;
>>> -        CollisionMap[PN] = Old;
>>> -        break;
>>> -      }
>>> -      // Proceed to the next PHI in the list.
>>> -      OtherPN = I->second;
>>> +  bool Changed = false;
>>> +  for (auto I = BB->begin(); PHINode *PN = dyn_cast<PHINode>(I++);) {
>>> +    auto Inserted = PHISet.insert(PN);
>>> +    if (!Inserted.second) {
>>> +      // A duplicate. Replace this PHI with its duplicate.
>>> +      PN->replaceAllUsesWith(*Inserted.first);
>>> +      PN->eraseFromParent();
>>> +      Changed = true;
>>>        }
>>>      }
>>>
>>>
>>>
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>>>
>>>
>>
> --
> Jon Roelofs
> jonathan at codesourcery.com
> CodeSourcery / Mentor Embedded
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