8229897: [lworld] C1 should avoid allocation when reading a field from a flattened field

[fparain]

Please review this patch which removes temporary heap allocations when reading a field from a flattened field.

During the HIR graph construction, C1 detects sequences of consecutive getfield bytecodes involving flattened fields and optimizes them with a single LoadField or NewInlineTypeInstance directly to the offset of the last nested field.

Performance improvement on a simple benchmark

static inline class Point {
    int i = 0, j = 0;
}
static inline class Rectangle {
    Point p0 = new Point(), p1 = new Point();
}
static class NamedRectangle {
    Rectangle rect = new Rectangle();
    String name;
}
static NamedRectangle nr = new NamedRectangle();
@Benchmark
public void testGetfieldChain1(Blackhole blackhole) {
    int i = nr.rect.p0.j;                                                              // reads two flattened fields before reading an int
    blackhole.consume(i);
}

@Benchmark
public void testGetfieldChain2(Blackhole blackhole) {
    Point p = nr.rect.p1;                                                          // reads a flattened field inside a flattened field
    blackhole.consume(p);
}

Without the optimization:
Benchmark Mode Samples Score Score error Units
o.s.MyBenchmark.testGetfieldChain1 avgt 200 8.696 0.024 ns/op
o.s.MyBenchmark.testGetfieldChain2 avgt 200 8.969 0.027 ns/op

With the optimization:
Benchmark Mode Samples Score Score error Units
o.s.MyBenchmark.testGetfieldChain1 avgt 200 2.134 0.019 ns/op
o.s.MyBenchmark.testGetfieldChain2 avgt 200 5.150 0.017 ns/op

Tested with Mach5, tiers 1 to 3.

Thank you,

Fred

---

Progress

• Change must not contain extraneous whitespace

Issue

• JDK-8229897: [lworld] C1 should avoid allocation when reading a field from a flattened field

Reviewers

• Tobias Hartmann (thartmann - Committer)

Download

$ git fetch https://git.openjdk.java.net/valhalla pull/167/head:pull/167
$ git checkout pull/167

[bridgekeeper]

👋 Welcome back fparain! A progress list of the required criteria for merging this PR into lworld will be added to the body of your pull request.

[openjdk]

@fparain This change now passes all automated pre-integration checks, type /integrate in a new comment to proceed. After integration, the commit message will be:

8229897: [lworld] C1 should avoid allocation when reading a field from a flattened field

Reviewed-by: thartmann

• If you would like to add a summary, use the /summary command.
• To credit additional contributors, use the /contributor command.
• To add additional solved issues, use the /issue command.

There are currently no new commits on the lworld branch since the last update of the source branch of this PR. If another commit should be pushed before you perform the /integrate command, your PR will be automatically rebased. If you would like to avoid potential automatic rebasing, specify the current head hash when integrating, like this: /integrate 54b541094689d6244b95307724f9a9698c10e46d.

➡️ To integrate this PR with the above commit message to the lworld branch, type /integrate in a new comment.

[mlbridge]

Webrevs

• 00: Full (349b26a)

[TobiHartmann]

Looks good to me!

[fparain]

Thanks Tobias!

Fred

[fparain]

/integrate

[openjdk]

@fparain
Pushed as commit 3540dd4.