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cmd/compile: use edge weights to decide inlineability in PGO

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Currently, with PGO, the inliner uses node weights to decide if a
function is inlineable (with a larger budget). But the actual
inlining is determined by the weight of the call edge. There is a
discrepancy that, if a callee node is hot but the call edge is not,
it would not inlined, and marking the callee inlineable would of
no use.

Instead of using two kinds of weights, we just use the edge
weights to decide inlineability. If a function is the callee of a
hot call edge, its inlineability is determined with a larger
threshold. For a function that exceeds the regular inlining budget,
it is still inlined only when the call edge is hot, as it would
exceed the regular inlining cost for non-hot call sites, even if
it is marked inlineable.

For #55022.

Change-Id: I93fa9919fc6bcbb394e6cfe54ec96a96eede08f7
Reviewed-on: https://go-review.googlesource.com/c/go/+/447015
Run-TryBot: Cherry Mui <cherryyz@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
This commit is contained in:
Cherry Mui 2022-11-01 11:40:29 -04:00
parent a5b4283dfd
commit fb4f7fdb26
3 changed files with 8 additions and 25 deletions
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1
src/cmd/compile/internal/base/debug.go
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@ -46,7 +46,6 @@ type DebugFlags struct {
WB int `help:"print information about write barriers"`
ABIWrap int `help:"print information about ABI wrapper generation"`
MayMoreStack string `help:"call named function before all stack growth checks"`
InlineHotFuncThreshold string `help:"threshold percentage for determining functions as hot candidates for inlining"`
InlineHotCallSiteThreshold string `help:"threshold percentage for determining call sites as hot candidates for inlining"`
InlineHotBudget int `help:"inline budget for hot functions"`
PGOInline int `help:"debug profile-guided inlining"`