[lworld] RFR: 8251046: [lworld] [lw3] C1 should avoid heap allocations in withfield when possible [v3]

[Frederic Parain]

> Please review this patch which reduces the number of heap allocations when executing the withfield bytecode with C1.
> The CR linked below contains a more detailed description of the optimization:
> 
> CR: https://bugs.openjdk.java.net/browse/JDK-8251046
> 
> A rudimentary benchmark shows encouraging numbers:
> Measuring inline type creation time with -XX:TieredStopAtLevel=1
> Inline class Point has two int fields.
> Inline class Rectangle has four int fields.
> 
> Without the optimization:
> Benchmark                                Mode  Samples   Score  Score error  Units
> o.s.MyBenchmark.testPointCreation        avgt      200   7.573        0.027  ns/op
> o.s.MyBenchmark.testRectangleCreation    avgt      200  21.387        0.067  ns/op
> 
> With the optimization:
> Benchmark                                Mode  Samples  Score  Score error  Units
> o.s.MyBenchmark.testPointCreation        avgt      200  5.284        0.014  ns/op
> o.s.MyBenchmark.testRectangleCreation    avgt      200  7.750        0.082  ns/op
> 
> Tested manually and with Mach5, tiers 1 to 3 (with Tobias' changes enabling more C1 testing).
> 
> Thank you,
> 
> Fred

Frederic Parain has updated the pull request incrementally with one additional commit since the last revision:

  Fix indentation

-------------

Changes:
  - all: https://git.openjdk.java.net/valhalla/pull/137/files
  - new: https://git.openjdk.java.net/valhalla/pull/137/files/c30c64a0..88bd48e4

Webrevs:
 - full: https://webrevs.openjdk.java.net/valhalla/137/webrev.02
 - incr: https://webrevs.openjdk.java.net/valhalla/137/webrev.01-02

  Stats: 4 lines in 1 file changed: 0 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/137.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/137/head:pull/137

PR: https://git.openjdk.java.net/valhalla/pull/137