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Re-order some blocks in runtimelookup #83453

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EgorBo wants to merge 8 commits into from
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Re-order some blocks in runtimelookup #83453

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8894243
Re-order some blocks in runtimelookup
EgorBo Mar 15, 2023
65a2e0b
Update runtimelookup.cpp
EgorBo Mar 15, 2023
05293dc
Update runtimelookup.cpp
EgorBo Mar 15, 2023
61b02a5
Merge branch 'main' of github.com:dotnet/runtime into runtimelookup-r…
EgorBo Mar 21, 2023
4f2b996
Merge branch 'main' of github.com:dotnet/runtime into runtimelookup-r…
EgorBo Mar 28, 2023
9311a11
mark blocks cold
EgorBo Mar 29, 2023
73b458b
Restore fgReorderBlocks
EgorBo Mar 29, 2023
2505631
actually we don't need them, let's rely on OptimizeLayout phase
EgorBo Mar 29, 2023
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44 changes: 14 additions & 30 deletions src/coreclr/jit/runtimelookup.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -224,7 +224,6 @@ PhaseStatus Compiler::fgExpandRuntimeLookups()
}

GenTree* ctxTree = call->gtArgs.GetArgByIndex(0)->GetNode();
GenTree* sigNode = call->gtArgs.GetArgByIndex(1)->GetNode();

// Prepare slotPtr tree (TODO: consider sharing this part with impRuntimeLookup)
GenTree* slotPtrTree = gtCloneExpr(ctxTree);
Expand Down Expand Up @@ -275,11 +274,11 @@ PhaseStatus Compiler::fgExpandRuntimeLookups()
// if (*fastPathValue == null)
// goto fallbackBb;
//
// fastPathBb(BBJ_ALWAYS): [weight: 0.8]
// fastPathBb(BBJ_ALWAYS): [weight: 1.0]
// rtLookupLcl = *fastPathValue;
// goto block;
//
// fallbackBb(BBJ_NONE): [weight: 0.2]
// fallbackBb(BBJ_NONE): [weight: 0.0]
// rtLookupLcl = HelperCall();
//
// block(...): [weight: 1.0]
Expand Down Expand Up @@ -320,15 +319,15 @@ PhaseStatus Compiler::fgExpandRuntimeLookups()
// goto fallbackBb;
// ...
//
// nullcheckBb(BBJ_COND): [weight: 0.8]
// nullcheckBb(BBJ_COND): [weight: 1.0]
// if (*fastPathValue == null)
// goto fallbackBb;
//
// fastPathBb(BBJ_ALWAYS): [weight: 0.64]
// fastPathBb(BBJ_ALWAYS): [weight: 1.0]
// rtLookupLcl = *fastPathValue;
// goto block;
//
// fallbackBb(BBJ_NONE): [weight: 0.36]
// fallbackBb(BBJ_NONE): [weight: 0.0]
// rtLookupLcl = HelperCall();
//
// block(...): [weight: 1.0]
Expand Down Expand Up @@ -387,27 +386,15 @@ PhaseStatus Compiler::fgExpandRuntimeLookups()

//
// Re-distribute weights (see '[weight: X]' on the diagrams above)
// TODO: consider marking fallbackBb as rarely-taken
//
block->inheritWeight(prevBb);
if (needsSizeCheck)
{
sizeCheckBb->inheritWeight(prevBb);
// 80% chance we pass nullcheck
nullcheckBb->inheritWeightPercentage(sizeCheckBb, 80);
// 64% (0.8 * 0.8) chance we pass both nullcheck and sizecheck
fastPathBb->inheritWeightPercentage(nullcheckBb, 80);
// 100-64=36% chance we fail either nullcheck or sizecheck
fallbackBb->inheritWeightPercentage(sizeCheckBb, 36);
}
else
{
nullcheckBb->inheritWeight(prevBb);
// 80% chance we pass nullcheck
fastPathBb->inheritWeightPercentage(nullcheckBb, 80);
// 20% chance we fail nullcheck (TODO: Consider making it cold (0%))
fallbackBb->inheritWeightPercentage(nullcheckBb, 20);
}
nullcheckBb->inheritWeight(prevBb);
fastPathBb->inheritWeight(prevBb);
fallbackBb->bbSetRunRarely();

//
// Update loop info if loop table is known to be valid
Expand Down Expand Up @@ -437,6 +424,12 @@ PhaseStatus Compiler::fgExpandRuntimeLookups()
assert(BasicBlock::sameEHRegion(prevBb, sizeCheckBb));
}

// Merge prevBb with nullcheckBb (or sizeBb) if possible to simplify layout
if (fgCanCompactBlocks(prevBb, prevBb->GetUniqueSucc()))
{
fgCompactBlocks(prevBb, prevBb->GetUniqueSucc());
}

// Scan current block again, the current call will be ignored because of ClearExpRuntimeLookup.
// We don't try to re-use expansions for the same lookups in the current block here - CSE is responsible
// for that
Expand All @@ -447,14 +440,5 @@ PhaseStatus Compiler::fgExpandRuntimeLookups()
}
}
}

if (result == PhaseStatus::MODIFIED_EVERYTHING)
{
if (opts.OptimizationEnabled())
{
fgReorderBlocks(/* useProfileData */ false);
fgUpdateChangedFlowGraph(FlowGraphUpdates::COMPUTE_BASICS);
}
}
Comment on lines -451 to -458
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@jakobbotsch jakobbotsch Mar 15, 2023

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W.r.t. the confusing diffs, maybe try with this change reverted?

return result;
}