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hottest one
When both a direct call and an interface call appear on the same line,
PGO devirtualization may make a suboptimal decision. In some cases,
the directly called function becomes a candidate for devirtualization
if no other relevant outgoing edges with non-zero weight exist for the
caller's IRNode in the WeightedCG. The edge to this candidate is
considered the hottest. Despite having zero weight, this edge still
causes the interface call to be devirtualized.
This CL prevents devirtualization when the weight of the hottest edge
is 0.
Fixes #72092
Change-Id: I06c0c5e080398d86f832e09244aceaa4aeb98721
Reviewed-on: https://go-review.googlesource.com/c/go/+/655475
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
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The processing performed in cmd/preprofile is a simple version of the
same initial processing performed by cmd/compile/internal/pgo. Refactor
this processing into the new IR-independent cmd/internal/pgo package.
Now cmd/preprofile and cmd/compile run the same code for initial
processing of a pprof profile, guaranteeing that they always stay in
sync.
Since it is now trivial, this CL makes one change to the serialization
format: the entries are ordered by weight. This allows us to avoid
sorting ByWeight on deserialization.
Impact on PGO parsing when compiling cmd/compile with PGO:
* Without preprocessing: PGO parsing ~13.7% of CPU time
* With preprocessing (unsorted): ~2.9% of CPU time (sorting ~1.7%)
* With preprocessing (sorted): ~1.3% of CPU time
The remaining 1.3% of CPU time approximately breaks down as:
* ~0.5% parsing the preprocessed profile
* ~0.7% building weighted IR call graph
* ~0.5% walking function IR to find direct calls
* ~0.2% performing lookups for indirect calls targets
For #58102.
Change-Id: Iaba425ea30b063ca195fb2f7b29342961c8a64c2
Reviewed-on: https://go-review.googlesource.com/c/go/+/569337
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
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The call site calculation in the previous version is incorrect. For
the PGO preprocess file, the compiler should directly use the call
site offset value. Additionly, this change refactors the preprocess
tool to clean up unused fields including startline, the flat and the
cum.
Change-Id: I7bffed3215d4c016d9a9e4034bfd373bf50ab43f
Reviewed-on: https://go-review.googlesource.com/c/go/+/562795
Reviewed-by: Cherry Mui <cherryyz@google.com>
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As of CL 539699, PGO-based devirtualization supports devirtualization of
function values in addition to interface method calls. As with CL
497175, we need to explicitly look up functions from export data that
may not be imported already.
Symbol naming is ambiguous (`foo.Bar.func1` could be a closure or a
method), so we simply attempt to do both types of lookup. That said,
closures are defined in export data only as OCLOSURE nodes in the
enclosing function, which this CL does not yet attempt to expand.
For #61577.
Change-Id: Ic7205b046218a4dfb8c4162ece3620ed1c3cb40a
Reviewed-on: https://go-review.googlesource.com/c/go/+/540258
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
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Today, PGO-based devirtualization only applies to interface calls. This
CL extends initial support to function values (i.e., function/closure
pointers passed as arguments or stored in a struct).
This CL is a minimal implementation with several limitations.
* Export data lookup of function value callees not implemented
(equivalent of CL 497175; done in CL 540258).
* Callees must be standard static functions. Callees that are closures
(requiring closure context) are not supported.
For #61577.
Change-Id: I7d328859035249e176294cd0d9885b2d08c853f6
Reviewed-on: https://go-review.googlesource.com/c/go/+/539699
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
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Today, the PGO IR graph only contains entries for ir.Func loaded into
the package. This can include functions from transitive dependencies,
but only if they happen to be referenced by something in the current
package. If they are not referenced, noder never bothers to load them.
This leads to a deficiency in PGO devirtualization: some callee methods
are available in transitive dependencies but do not devirtualize because
they happen to not get loaded from export data.
Resolve this by adding an explicit lookup from export data of callees
mentioned in the profile.
I have chosen to do this during loading of the profile for simplicity:
the PGO IR graph always contains all of the functions we might need.
That said, it isn't strictly necessary. PGO devirtualization could do
the lookup lazily if it decides it actually needs a method. This saves
work at the expense of a bit more complexity, but I've chosen the
simpler approach for now as I measured the cost of this as significantly
less than the rest of PGO loading.
For #61577.
Change-Id: Ieafb2a549510587027270ee6b4c3aefd149a901f
Reviewed-on: https://go-review.googlesource.com/c/go/+/497175
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
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if current package has a concrete reference
The new PGO-driven indirect call specialization from CL 492436
in theory should allow for devirtualization on methods
in another package when those methods are directly referenced
in the current package.
However, inline.InlineImpossible was checking for a zero-length
fn.Body and would cause devirtualization to fail
with a debug log message like:
"should not PGO devirtualize (*Speaker1).Speak: no function body"
Previously, the logic in inline.InlineImpossible was only
called on local functions, but with PGO-based devirtualization,
it can now be called on imported functions, where inlinable
imported functions will have a zero-length fn.Body but a
non-nil fn.Inl.
We update inline.InlineImpossible to handle imported functions
by adding a call to typecheck.HaveInlineBody in the check
that was previously failing.
For the test, we need to have a hopefully temporary workaround
of adding explicit references to the callees in another package
for devirtualization to work. CL 497175 or similar should
enable removing this workaround.
Fixes #60561
Updates #59959
Change-Id: I48449b7d8b329d84151bd3b506b8093c262eb2a3
GitHub-Last-Rev: 2d53c55fd895ad8fefd25510a6e6969e89d54a6d
GitHub-Pull-Request: golang/go#60565
Reviewed-on: https://go-review.googlesource.com/c/go/+/500155
Run-TryBot: thepudds <thepudds1460@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
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This CL is originally based on CL 484838 from rajbarik@uber.com.
Add a new PGO-based devirtualize pass. This pass conditionally
devirtualizes interface calls for the hottest callee. That is, it
performs a transformation like:
type Iface interface {
Foo()
}
type Concrete struct{}
func (Concrete) Foo() {}
func foo(i Iface) {
i.Foo()
}
to:
func foo(i Iface) {
if c, ok := i.(Concrete); ok {
c.Foo()
} else {
i.Foo()
}
}
The primary benefit of this transformation is enabling inlining of the
direct calls.
Today this change has no impact on the escape behavior, as the fallback
interface always forces an escape. But improving escape analysis to take
advantage of this is an area of potential work.
This CL is the bare minimum of a devirtualization implementation. There
are still numerous limitations:
* Callees not directly referenced in the current package can be missed
(even if they are in the transitive dependences).
* Callees not in the transitive dependencies of the current package are
missed.
* Only interface method calls are supported, not other indirect function
calls.
* Multiple calls to compatible interfaces on the same line cannot be
distinguished and will use the same callee target.
* Callees that only partially implement an interface (they are embedded
in another type that completes the interface) cannot be devirtualized.
* Others, mentioned in TODOs.
Fixes #59959
Change-Id: I8bedb516139695ee4069650b099d05957b7ce5ee
Reviewed-on: https://go-review.googlesource.com/c/go/+/492436
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
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