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[ScheduleDAG] Fix and simplify the algorithm used for finding callseq_start #149692

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85 changes: 41 additions & 44 deletions llvm/lib/CodeGen/SelectionDAG/ScheduleDAGRRList.cpp
Original file line number Diff line number Diff line change
Expand Up @@ -478,62 +478,61 @@ static bool IsChainDependent(SDNode *Outer, SDNode *Inner,
}
}

/// FindCallSeqStart - Starting from the (lowered) CALLSEQ_END node, locate
/// findCallSeqStart - Starting from the (lowered) CALLSEQ_END node, locate
/// the corresponding (lowered) CALLSEQ_BEGIN node.
///
/// NestLevel and MaxNested are used in recursion to indcate the current level
/// of nesting of CALLSEQ_BEGIN and CALLSEQ_END pairs, as well as the maximum
/// level seen so far.
///
/// TODO: It would be better to give CALLSEQ_END an explicit operand to point
/// to the corresponding CALLSEQ_BEGIN to avoid needing to search for it.
static SDNode *
FindCallSeqStart(SDNode *N, unsigned &NestLevel, unsigned &MaxNest,
const TargetInstrInfo *TII) {
while (true) {
// For a TokenFactor, examine each operand. There may be multiple ways
// to get to the CALLSEQ_BEGIN, but we need to find the path with the
// most nesting in order to ensure that we find the corresponding match.
static SDNode *findCallSeqStart(SDNode *CallSeqEnd,
const TargetInstrInfo *TII) {
SmallVector<SDNode *> DFSStack;
SmallPtrSet<SDNode *, 8> Visited;
unsigned CallSeqDepth = 0;

DFSStack.push_back(CallSeqEnd);
Visited.insert(CallSeqEnd);

while (!DFSStack.empty()) {
SDNode *N = DFSStack.back();

if (N->getOpcode() == ISD::TokenFactor) {
SDNode *Best = nullptr;
unsigned BestMaxNest = MaxNest;
for (const SDValue &Op : N->op_values()) {
unsigned MyNestLevel = NestLevel;
unsigned MyMaxNest = MaxNest;
if (SDNode *New = FindCallSeqStart(Op.getNode(),
MyNestLevel, MyMaxNest, TII))
if (!Best || (MyMaxNest > BestMaxNest)) {
Best = New;
BestMaxNest = MyMaxNest;
}
if (!Visited.insert(Op.getNode()).second)
continue;
DFSStack.push_back(Op.getNode());
break;
}
assert(Best);
MaxNest = BestMaxNest;
return Best;
if (DFSStack.back() == N)
DFSStack.pop_back();
continue;
}
// Check for a lowered CALLSEQ_BEGIN or CALLSEQ_END.

// Not a TokenFactor, no need to keep it in the DFS stack.
DFSStack.pop_back();

if (N->isMachineOpcode()) {
if (N->getMachineOpcode() == TII->getCallFrameDestroyOpcode()) {
++NestLevel;
MaxNest = std::max(MaxNest, NestLevel);
++CallSeqDepth;
} else if (N->getMachineOpcode() == TII->getCallFrameSetupOpcode()) {
assert(NestLevel != 0);
--NestLevel;
if (NestLevel == 0)
assert(CallSeqDepth);
if (--CallSeqDepth == 0)
return N;
}
}
// Otherwise, find the chain and continue climbing.
for (const SDValue &Op : N->op_values())
if (Op.getValueType() == MVT::Other) {
N = Op.getNode();
goto found_chain_operand;
}
return nullptr;
found_chain_operand:;
if (N->getOpcode() == ISD::EntryToken)
return nullptr;

// Find the chain and continue climbing.
// A SDNode should only have a single input chain.
auto OpValues = N->op_values();
auto ItChain = find_if(OpValues, [](const SDValue &Op) {
return Op.getValueType() == MVT::Other;
});
if (ItChain != OpValues.end() &&
(*ItChain)->getOpcode() != ISD::EntryToken &&
Visited.insert((*ItChain).getNode()).second)
DFSStack.push_back((*ItChain).getNode());
}

return nullptr;
}

/// Call ReleasePred for each predecessor, then update register live def/gen.
Expand Down Expand Up @@ -581,9 +580,7 @@ void ScheduleDAGRRList::ReleasePredecessors(SUnit *SU) {
for (SDNode *Node = SU->getNode(); Node; Node = Node->getGluedNode())
if (Node->isMachineOpcode() &&
Node->getMachineOpcode() == TII->getCallFrameDestroyOpcode()) {
unsigned NestLevel = 0;
unsigned MaxNest = 0;
SDNode *N = FindCallSeqStart(Node, NestLevel, MaxNest, TII);
SDNode *N = findCallSeqStart(Node, TII);
assert(N && "Must find call sequence start");

SUnit *Def = &SUnits[N->getNodeId()];
Expand Down
31 changes: 31 additions & 0 deletions llvm/test/CodeGen/M68k/PR146213.ll
Original file line number Diff line number Diff line change
@@ -0,0 +1,31 @@
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
; RUN: llc < %s -mtriple=m68k-linux | FileCheck %s

define double @minimized() nounwind {
; CHECK-LABEL: minimized:
; CHECK: ; %bb.0: ; %start
; CHECK-NEXT: suba.l #20, %sp
; CHECK-NEXT: movem.l %a2, (16,%sp) ; 8-byte Folded Spill
; CHECK-NEXT: move.l #0, (4,%sp)
; CHECK-NEXT: move.l #0, (%sp)
; CHECK-NEXT: jsr $0
; CHECK-NEXT: suba.l %a2, %a2
; CHECK-NEXT: move.l (%a2), (%sp)
; CHECK-NEXT: move.l #0, (12,%sp)
; CHECK-NEXT: move.l #0, (8,%sp)
; CHECK-NEXT: move.l $4, (4,%sp)
; CHECK-NEXT: jsr __muldf3
; CHECK-NEXT: move.l %d0, (%a2)
; CHECK-NEXT: move.l %d1, $4
; CHECK-NEXT: move.l %a2, %d0
; CHECK-NEXT: move.l %a2, %d1
; CHECK-NEXT: movem.l (16,%sp), %a2 ; 8-byte Folded Reload
; CHECK-NEXT: adda.l #20, %sp
; CHECK-NEXT: rts
start:
%_58 = call double null(double 0.000000e+00)
%_60 = load double, ptr null, align 8
%_57 = fmul double 0.000000e+00, %_60
store double %_57, ptr null, align 8
ret double 0.000000e+00
}
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