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[CodeGen] Preserve LiveStack analysis in StackSlotColoring pass #94967

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[CodeGen] Preserve LiveStack analysis in StackSlotColoring pass #94967

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e13e0f8
[CodeGen] Preserve LiveStack analysis in StackSlotColoring pass
vg0204 Jun 10, 2024
b0c08a6
preserved LS analysis by clearing the info not needed anymore.
vg0204 Jun 11, 2024
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7 changes: 7 additions & 0 deletions llvm/lib/CodeGen/StackSlotColoring.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -149,6 +149,7 @@ namespace {
AU.addRequired<SlotIndexes>();
AU.addPreserved<SlotIndexes>();
AU.addRequired<LiveStacks>();
AU.addPreserved<LiveStacks>();
AU.addRequired<MachineBlockFrequencyInfo>();
AU.addPreserved<MachineBlockFrequencyInfo>();
AU.addPreservedID(MachineDominatorsID);
Expand Down Expand Up @@ -534,6 +535,12 @@ bool StackSlotColoring::runOnMachineFunction(MachineFunction &MF) {
InitializeSlots();
Changed = ColorSlots(MF);

// Clear LiveStack analysis as it has been changed in ways that it requires
// efforts to rectify which is equivalent to do it all over again. Also,
// this current results would not be used later, so better to clear it &
// preserve analysis.
LS->releaseMemory();
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If you're just going to throw away the result there's no point in claiming this is preserved, since it's a lie

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But, currently LiveStack analysis really is doing nothing just creating a empty shell result, & real work is happening at RA to compute and update livestack result. Also, once generated at RA pass, spill entries in LS will later be used at stackSlotColoring pass, followed by not being used ever again (LS later be used during SCC pass coming after later RA passes, but at that point RA is concerned with newly introduced spill records in LS by itself). So, my point is that preserving LS won't help out in any way. And LS analyis itself is doing no computation, so its re-occurence should not have impact on performance.


for (int &Next : NextColors)
Next = -1;

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