Inliner uses capacity of locals table instead of count

[jakobbotsch]

I noticed in #69117 (comment) that we are using lvaTableCnt instead of lvaCount here:

runtime/src/coreclr/jit/inlinepolicy.cpp

Lines 1708 to 1714 in 96db556

	if (m_RootCompiler->lvaTableCnt > 64)
	{
	// E.g. MaxLocalsToTrack = 1024 and lvaTableCnt = 512 -> multiplier *= 0.5;
	const double lclFullness = min(1.0, (double)m_RootCompiler->lvaTableCnt / JitConfig.JitMaxLocalsToTrack());
	multiplier *= (1.0 - lclFullness);
	JITDUMP("\nCaller has %d locals. Multiplier decreased to %g.", m_RootCompiler->lvaTableCnt, multiplier);
	}

That seems strange and might cause significantly different inlining decisions just by adding or removing very few locals, depending on whether we grow the table one more time or not.

category:correctness
theme:inlining
skill-level:intermediate
cost:medium
impact:medium

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Issue Details

---

I noticed in #69117 (comment) that we are using lvaTableCnt instead of lvaCount here:

runtime/src/coreclr/jit/inlinepolicy.cpp

Lines 1708 to 1714 in 96db556

	if (m_RootCompiler->lvaTableCnt > 64)
	{
	// E.g. MaxLocalsToTrack = 1024 and lvaTableCnt = 512 -> multiplier *= 0.5;
	const double lclFullness = min(1.0, (double)m_RootCompiler->lvaTableCnt / JitConfig.JitMaxLocalsToTrack());
	multiplier *= (1.0 - lclFullness);
	JITDUMP("\nCaller has %d locals. Multiplier decreased to %g.", m_RootCompiler->lvaTableCnt, multiplier);
	}

That seems strange and might cause significantly different inlining decisions just by adding or removing very few locals, depending on whether we grow the table one more time or not.

Author:	jakobbotsch
Assignees:	-
Labels:	area-CodeGen-coreclr, untriaged
Milestone:	-

[AndyAyersMS]

@EgorBo please take a look once you're back.

[EgorBo]

Decided to postpone this to 8.0 where I plan more changes for the inliner. I tried this locally and it was too impactful