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[NFC][LoopVectorize] Make replaceVPBBWithIRVPBB more efficient #111514

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Merged
merged 4 commits into from
Oct 15, 2024
Merged

[NFC][LoopVectorize] Make replaceVPBBWithIRVPBB more efficient #111514

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389ab09
[NFC][LoopVectorize] Make replaceVPBBWithIRVPBB more efficient
david-arm Oct 8, 2024
6c45224
Address review comments
david-arm Oct 11, 2024
3da4e4e
Make new replaceXYZ functions private
david-arm Oct 14, 2024
d1b45da
Ensure reassociateBlocks leaves Old and New in a decent state
david-arm Oct 15, 2024
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10 changes: 3 additions & 7 deletions llvm/lib/Transforms/Vectorize/VPlan.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1004,13 +1004,9 @@ static void replaceVPBBWithIRVPBB(VPBasicBlock *VPBB, BasicBlock *IRBB) {
assert(!R.isPhi() && "Tried to move phi recipe to end of block");
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While we're here, worth adding in documentation above that VPBB, having a single predecessor, is expected to be free of phi recipes. A more informative error message may be "VPBB to be replaced by IRBB must be free of phi recipes".

Note that, in general, replacing a VPBB with an IRBB is a temporary solution, until the full skeleton is built in VPlan. Blocks would clearly be identified as IRBB's or not, from the outset.

R.moveBefore(*IRVPBB, IRVPBB->end());
}
VPBlockBase *PredVPBB = VPBB->getSinglePredecessor();
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This assert of having a single predecessor is now lost, yet still documented. The function traverses multiple predecessors, but probably works and tested for single predecessor only, as VPBB is still expected to be free of phi recipes? Better be clear, assert and test what is supported.

VPBlockUtils::disconnectBlocks(PredVPBB, VPBB);
VPBlockUtils::connectBlocks(PredVPBB, IRVPBB);
for (auto *Succ : to_vector(VPBB->getSuccessors())) {
VPBlockUtils::connectBlocks(IRVPBB, Succ);
VPBlockUtils::disconnectBlocks(VPBB, Succ);
}

VPBlockUtils::reassociateBlocks(VPBB, IRVPBB);

delete VPBB;
}

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33 changes: 33 additions & 0 deletions llvm/lib/Transforms/Vectorize/VPlan.h
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Expand Up @@ -440,6 +440,26 @@ class VPBlockBase {
Successors.erase(Pos);
}

/// This function replaces one predecessor with another, useful when
/// trying to replace an old block in the CFG with a new one.
void replacePredecessor(VPBlockBase *Old, VPBlockBase *New) {
auto I = find(Predecessors, Old);
assert(I != Predecessors.end());
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Error message missing.

assert(Old->getParent() == New->getParent() &&
"replaced predecessor must have the same parent");
*I = New;
}

/// This function replaces one successor with another, useful when
/// trying to replace an old block in the CFG with a new one.
void replaceSuccessor(VPBlockBase *Old, VPBlockBase *New) {
auto I = find(Successors, Old);
assert(I != Successors.end());
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Error message missing.

assert(Old->getParent() == New->getParent() &&
"replaced successor must have the same parent");
*I = New;
}

protected:
VPBlockBase(const unsigned char SC, const std::string &N)
: SubclassID(SC), Name(N) {}
Expand Down Expand Up @@ -3862,6 +3882,19 @@ class VPBlockUtils {
To->removePredecessor(From);
}

/// Reassociate all the blocks connected to \p Old so that they now point to
/// \p New.
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Suggested change
/// \p New.
/// \p New instead.

static void reassociateBlocks(VPBlockBase *Old, VPBlockBase *New) {
for (auto *Pred : to_vector(Old->getPredecessors()))
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Is this to_vector() needed, given that Old's predecessors remain intact?

Pred->replaceSuccessor(Old, New);
for (auto *Succ : to_vector(Old->getSuccessors()))
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Is this to_vector() needed, given that Old's successors remain intact?

Succ->replacePredecessor(Old, New);
New->setPredecessors(Old->getPredecessors());
New->setSuccessors(Old->getSuccessors());
Old->clearPredecessors();
Old->clearSuccessors();
}

/// Return an iterator range over \p Range which only includes \p BlockTy
/// blocks. The accesses are casted to \p BlockTy.
template <typename BlockTy, typename T>
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