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LiveRangeShrink: Early exit when encountering a code motion barrier. #136806

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Merged
merged 4 commits into from
Apr 24, 2025
Merged

LiveRangeShrink: Early exit when encountering a code motion barrier. #136806

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[𝘀𝗽𝗿] changes to main this commit is based on
pcc Apr 23, 2025
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[𝘀𝗽𝗿] initial version
pcc Apr 23, 2025
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[𝘀𝗽𝗿] changes introduced through rebase
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pcc Apr 23, 2025
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15 changes: 12 additions & 3 deletions llvm/lib/CodeGen/LiveRangeShrink.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -95,14 +95,24 @@ static MachineInstr *FindDominatedInstruction(MachineInstr &New,
return Old;
}

static bool isCodeMotionBarrier(MachineInstr &MI) {
return MI.hasUnmodeledSideEffects() && !MI.isPseudoProbe();
}
Comment on lines +102 to +104
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@arsenm arsenm Apr 23, 2025

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Document this? What is the exact problematic condition? We have several different barrier concepts already spread in MachineInstr and TargetInstrInfo, can we use one of those

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@pcc pcc Apr 23, 2025

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Added a comment that describes the situation to the best of my understanding. I don't think the existing ones can be used because the condition is specific to what this pass is doing.


/// Builds Instruction to its dominating order number map \p M by traversing
/// from instruction \p Start.
static void BuildInstOrderMap(MachineBasicBlock::iterator Start,
InstOrderMap &M) {
M.clear();
unsigned i = 0;
for (MachineInstr &I : make_range(Start, Start->getParent()->end()))
bool SawStore = false;
for (MachineInstr &I : make_range(Start, Start->getParent()->end())) {
if (I.mayStore())
SawStore = true;
if (!I.isSafeToMove(SawStore) && isCodeMotionBarrier(I))
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@arsenm arsenm Apr 23, 2025

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The MI.hasUnmodeledSideEffects() is redundant with the isSafeToMove check?

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@pcc pcc Apr 23, 2025

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Correct, updated this code to only call one.

While reading the code I observed that the code to update SawStore in this pass is redundant with what isSafeToMove is doing, so I removed it.

break;
M[&I] = i++;
}
}

bool LiveRangeShrink::runOnMachineFunction(MachineFunction &MF) {
Expand Down Expand Up @@ -166,8 +176,7 @@ bool LiveRangeShrink::runOnMachineFunction(MachineFunction &MF) {
// If MI has side effects, it should become a barrier for code motion.
// IOM is rebuild from the next instruction to prevent later
// instructions from being moved before this MI.
if (MI.hasUnmodeledSideEffects() && !MI.isPseudoProbe() &&
Next != MBB.end()) {
if (isCodeMotionBarrier(MI) && Next != MBB.end()) {
BuildInstOrderMap(Next, IOM);
SawStore = false;
}
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3 changes: 3 additions & 0 deletions llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
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Expand Up @@ -967,6 +967,9 @@ static void AddNodeIDCustom(FoldingSetNodeID &ID, const SDNode *N) {
case ISD::INTRINSIC_W_CHAIN:
// Handled by MemIntrinsicSDNode check after the switch.
break;
case ISD::MDNODE_SDNODE:
ID.AddPointer(cast<MDNodeSDNode>(N)->getMD());
break;
} // end switch (N->getOpcode())

// MemIntrinsic nodes could also have subclass data, address spaces, and flags
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