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Optimize DAGCombiner's worklist processing. Previously it started

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its work by putting all nodes in the worklist, requiring a big
dynamic allocation. Now, DAGCombiner just iterates over the AllNodes
list and maintains a worklist for nodes that are newly created or
need to be revisited. This allows the worklist to stay small in most
cases, so it can be a SmallVector.

This has the side effect of making DAGCombine not miss a folding
opportunity in alloca-align-rounding.ll.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@55498 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2008-08-28 21:01:56 +00:00
parent 9ffd8b5720
commit a3f8b7a4ce
2 changed files with 102 additions and 77 deletions
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177
lib/CodeGen/SelectionDAG/DAGCombiner.cpp
View File

@ -53,12 +53,31 @@ namespace {
bool AfterLegalize;
bool Fast;
// Create a dummy node (which is not added to allnodes), that adds a reference
// to the root node, preventing it from being deleted, and tracking any
// changes of the root.
HandleSDNode Dummy;
// Worklist of all of the nodes that need to be simplified.
std::vector<SDNode*> WorkList;
SmallVector<SDNode*, 8> WorkList;
// The current position of our iteration through the allnodes list.
SelectionDAG::allnodes_iterator CurNode;
// AA - Used for DAG load/store alias analysis.
AliasAnalysis &AA;
/// AdvanceCurNode - Update CurNode to point to the next node to process.
///
void AdvanceCurNode() {
// We start at the end of the list and work towards the front. Setting
// CurNode to DAG.allnodes_end() indicates that we're done.
if (CurNode == DAG.allnodes_begin())
CurNode = DAG.allnodes_end();
else
--CurNode;
}
/// AddUsersToWorkList - When an instruction is simplified, add all users of
/// the instruction to the work lists because they might get more simplified
/// now.
@ -86,6 +105,10 @@ namespace {
void removeFromWorkList(SDNode *N) {
WorkList.erase(std::remove(WorkList.begin(), WorkList.end(), N),
WorkList.end());
// If the next node we were planning to process is deleted,
// skip past it.
if (N == CurNode)
AdvanceCurNode();
}
SDValue CombineTo(SDNode *N, const SDValue *To, unsigned NumTo,
@ -243,10 +266,14 @@ public:
TLI(D.getTargetLoweringInfo()),
AfterLegalize(false),
Fast(fast),
Dummy(D.getRoot()),
AA(A) {}
/// Run - runs the dag combiner on all nodes in the work list
void Run(bool RunningAfterLegalize);
/// ProcessNode - runs the dag combiner on a node
void ProcessNode(SDNode *N);
};
}
@ -575,91 +602,89 @@ bool DAGCombiner::SimplifyDemandedBits(SDValue Op, const APInt &Demanded) {
// Main DAG Combiner implementation
//===----------------------------------------------------------------------===//
void DAGCombiner::ProcessNode(SDNode *N) {
// If N has no uses, it is dead. Make sure to revisit all N's operands once
// N is deleted from the DAG, since they too may now be dead or may have a
// reduced number of uses, allowing other xforms.
if (N->use_empty() && N != &Dummy) {
for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i)
AddToWorkList(N->getOperand(i).Val);
DAG.DeleteNode(N);
return;
}
SDValue RV = combine(N);
if (RV.Val == 0)
return;
++NodesCombined;
// If we get back the same node we passed in, rather than a new node or
// zero, we know that the node must have defined multiple values and
// CombineTo was used. Since CombineTo takes care of the worklist
// mechanics for us, we have no work to do in this case.
if (RV.Val == N)
return;
assert(N->getOpcode() != ISD::DELETED_NODE &&
RV.Val->getOpcode() != ISD::DELETED_NODE &&
"Node was deleted but visit returned new node!");
DOUT << "\nReplacing.3 "; DEBUG(N->dump(&DAG));
DOUT << "\nWith: "; DEBUG(RV.Val->dump(&DAG));
DOUT << '\n';
if (N->getNumValues() == RV.Val->getNumValues())
DAG.ReplaceAllUsesWith(N, RV.Val);
else {
assert(N->getValueType(0) == RV.getValueType() &&
N->getNumValues() == 1 && "Type mismatch");
SDValue OpV = RV;
DAG.ReplaceAllUsesWith(N, &OpV);
}
// Delete the old node.
removeFromWorkList(N);
DAG.DeleteNode(N);
// Push the new node and any users onto the worklist
AddToWorkList(RV.Val);
AddUsersToWorkList(RV.Val);
}
void DAGCombiner::Run(bool RunningAfterLegalize) {
// set the instance variable, so that the various visit routines may use it.
AfterLegalize = RunningAfterLegalize;
// Add all the dag nodes to the worklist.
WorkList.reserve(DAG.allnodes_size());
for (SelectionDAG::allnodes_iterator I = DAG.allnodes_begin(),
E = DAG.allnodes_end(); I != E; ++I)
WorkList.push_back(I);
// Create a dummy node (which is not added to allnodes), that adds a reference
// to the root node, preventing it from being deleted, and tracking any
// changes of the root.
HandleSDNode Dummy(DAG.getRoot());
// The root of the dag may dangle to deleted nodes until the dag combiner is
// done. Set it to null to avoid confusion.
DAG.setRoot(SDValue());
// while the worklist isn't empty, inspect the node on the end of it and
// try and combine it.
while (!WorkList.empty()) {
SDNode *N = WorkList.back();
WorkList.pop_back();
// If N has no uses, it is dead. Make sure to revisit all N's operands once
// N is deleted from the DAG, since they too may now be dead or may have a
// reduced number of uses, allowing other xforms.
if (N->use_empty() && N != &Dummy) {
for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i)
AddToWorkList(N->getOperand(i).Val);
DAG.DeleteNode(N);
continue;
// Process all the original dag nodes. We process starting from the
// end of the list and working forward, which is in roughly topological
// order. Starting at the end and working forward means we won't
// accidentally revisit nodes created during the dagcombine process.
CurNode = prior(DAG.allnodes_end());
do {
SDNode *N = &*CurNode;
AdvanceCurNode();
ProcessNode(N);
// Processing the node may have resulted in nodes being added to the
// worklist, because the were newly created or because one of their
// operands changed or some other reason they should be revisited.
// While the worklist isn't empty, inspect the node on the end of it
// and try and combine it.
while (!WorkList.empty()) {
SDNode *N = WorkList.back();
WorkList.pop_back();
if (N == CurNode)
AdvanceCurNode();
ProcessNode(N);
}
SDValue RV = combine(N);
if (RV.Val == 0)
continue;
++NodesCombined;
// If we get back the same node we passed in, rather than a new node or
// zero, we know that the node must have defined multiple values and
// CombineTo was used. Since CombineTo takes care of the worklist
// mechanics for us, we have no work to do in this case.
if (RV.Val == N)
continue;
assert(N->getOpcode() != ISD::DELETED_NODE &&
RV.Val->getOpcode() != ISD::DELETED_NODE &&
"Node was deleted but visit returned new node!");
} while (CurNode != DAG.allnodes_end());
DOUT << "\nReplacing.3 "; DEBUG(N->dump(&DAG));
DOUT << "\nWith: "; DEBUG(RV.Val->dump(&DAG));
DOUT << '\n';
WorkListRemover DeadNodes(*this);
if (N->getNumValues() == RV.Val->getNumValues())
DAG.ReplaceAllUsesWith(N, RV.Val, &DeadNodes);
else {
assert(N->getValueType(0) == RV.getValueType() &&
N->getNumValues() == 1 && "Type mismatch");
SDValue OpV = RV;
DAG.ReplaceAllUsesWith(N, &OpV, &DeadNodes);
}
// Push the new node and any users onto the worklist
AddToWorkList(RV.Val);
AddUsersToWorkList(RV.Val);
// Add any uses of the old node to the worklist in case this node is the
// last one that uses them. They may become dead after this node is
// deleted.
for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i)
AddToWorkList(N->getOperand(i).Val);
// Nodes can be reintroduced into the worklist. Make sure we do not
// process a node that has been replaced.
removeFromWorkList(N);
// Finally, since the node is now dead, remove it from the graph.
DAG.DeleteNode(N);
}
// If the root changed (e.g. it was a dead load, update the root).
DAG.setRoot(Dummy.getValue());
}

2
test/CodeGen/X86/alloca-align-rounding.ll
View File

@ -1,5 +1,5 @@
; RUN: llvm-as < %s | llc -march=x86 -mtriple=i686-apple-darwin | grep and | count 1
; RUN: llvm-as < %s | llc -march=x86-64 -mtriple=i686-pc-linux | grep and | count 3
; RUN: llvm-as < %s | llc -march=x86-64 -mtriple=i686-pc-linux | grep and | count 1
declare void @bar(<2 x i64>* %n)