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[SandboxVec][DAG] Avoid unnecessary dependency scan and improve description #112057

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Merged
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Oct 14, 2024
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[SandboxVec][DAG] Avoid unnecessary dependency scan and improve description #112057

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89 changes: 63 additions & 26 deletions llvm/lib/Transforms/Vectorize/SandboxVectorizer/DependencyGraph.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -276,30 +276,44 @@ Interval<Instruction> DependencyGraph::extend(ArrayRef<Instruction *> Instrs) {

// Create the dependencies.
//
// 1. DAGInterval empty 2. New is below Old 3. New is above old
// ------------------------ ------------------- -------------------
// Scan: DstN: Scan:
// +---+ -ScanTopN +---+DstTopN -ScanTopN
// | | | |New| |
// |Old| | +---+ -ScanBotN
// | | | +---+
// DstN: Scan: +---+DstN: | | |
// +---+DstTopN -ScanTopN +---+DstTopN | |Old|
// |New| | |New| | | |
// +---+DstBotN -ScanBotN +---+DstBotN -ScanBotN +---+DstBotN

// 1. This is a new DAG.
if (DAGInterval.empty()) {
assert(NewInterval == InstrsInterval && "Expected empty DAGInterval!");
auto DstRange = MemDGNodeIntervalBuilder::make(NewInterval, *this);
// 1. This is a new DAG, DAGInterval is empty. Fully scan the whole interval.
// +---+ - -
// | | SrcN | |
// | | | | SrcRange |
// |New| v | | DstRange
// | | DstN - |
// | | |
// +---+ -
// We are scanning for deps with destination in NewInterval and sources in
// NewInterval until DstN, for each DstN.
auto FullScan = [this](const Interval<Instruction> Intvl) {
auto DstRange = MemDGNodeIntervalBuilder::make(Intvl, *this);
if (!DstRange.empty()) {
for (MemDGNode &DstN : drop_begin(DstRange)) {
auto SrcRange = Interval<MemDGNode>(DstRange.top(), DstN.getPrevNode());
scanAndAddDeps(DstN, SrcRange);
}
}
};
if (DAGInterval.empty()) {
assert(NewInterval == InstrsInterval && "Expected empty DAGInterval!");
FullScan(NewInterval);
}
// 2. The new section is below the old section.
// +---+ -
// | | |
// |Old| SrcN |
// | | | |
// +---+ | | SrcRange
// +---+ | | -
// | | | | |
// |New| v | | DstRange
// | | DstN - |
// | | |
// +---+ -
// We are scanning for deps with destination in NewInterval because the deps
// in DAGInterval have already been computed. We consider sources in the whole
// range including both NewInterval and DAGInterval until DstN, for each DstN.
else if (DAGInterval.bottom()->comesBefore(NewInterval.top())) {
auto DstRange = MemDGNodeIntervalBuilder::make(NewInterval, *this);
auto SrcRangeFull = MemDGNodeIntervalBuilder::make(
Expand All @@ -312,16 +326,39 @@ Interval<Instruction> DependencyGraph::extend(ArrayRef<Instruction *> Instrs) {
}
// 3. The new section is above the old section.
else if (NewInterval.bottom()->comesBefore(DAGInterval.top())) {
auto DstRange = MemDGNodeIntervalBuilder::make(
NewInterval.getUnionInterval(DAGInterval), *this);
auto SrcRangeFull = MemDGNodeIntervalBuilder::make(NewInterval, *this);
if (!DstRange.empty()) {
for (MemDGNode &DstN : drop_begin(DstRange)) {
auto SrcRange =
Interval<MemDGNode>(SrcRangeFull.top(), DstN.getPrevNode());
scanAndAddDeps(DstN, SrcRange);
}
}
// +---+ - -
// | | SrcN | |
// |New| | | SrcRange | DstRange
// | | v | |
// | | DstN - |
// | | |
// +---+ -
// +---+
// |Old|
// | |
// +---+
// When scanning for deps with destination in NewInterval we need to fully
// scan the interval. This is the same as the scanning for a new DAG.
FullScan(NewInterval);

// +---+ -
// | | |
// |New| SrcN | SrcRange
// | | | |
// | | | |
// | | | |
// +---+ | -
// +---+ | -
// |Old| v | DstRange
// | | DstN |
// +---+ -
// When scanning for deps with destination in DAGInterval we need to
// consider sources from the NewInterval only, because all intra-DAGInterval
// dependencies have already been created.
auto DstRangeOld = MemDGNodeIntervalBuilder::make(DAGInterval, *this);
auto SrcRange = MemDGNodeIntervalBuilder::make(NewInterval, *this);
for (MemDGNode &DstN : DstRangeOld)
scanAndAddDeps(DstN, SrcRange);
} else {
llvm_unreachable("We don't expect extending in both directions!");
}
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