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Hi, I'd like to request a review for a C2 optimization for String. format() and String. formatted() with simple format strings: https: //github. com/openjdk/jdk/pull/29915 Summary ------- When String. format() or formatted() is called with a compile-time</div>
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<div class="__aliyun_email_body_block"><div style="font-family: Tahoma, Arial, STHeitiSC-Light, SimSun"><div style="clear: both;"><span >Hi,</span></div><div style="clear: both;"><br ><div style="clear: both;">I'd like to request a review for a C2 optimization for String.format()</div><div style="clear: both;">and String.formatted() with simple format strings:</div><div style="clear: both;"><br ></div><div style="clear: both;"><a href="https://github.com/openjdk/jdk/pull/29915" target="_blank">https://github.com/openjdk/jdk/pull/29915</a></div><div style="clear: both;"><br ></div><div style="clear: both;">Summary</div><div style="clear: both;">-------</div><div style="clear: both;">When String.format() or formatted() is called with a compile-time constant format string containing simple specifiers (%s, %d, %x, %X), this optimization</div><div style="clear: both;">bypasses the java.util.Formatter overhead and directly builds the result string.</div><div style="clear: both;">The C2 compiler recognizes these calls during the Parse phase and redirects them to specialized fast-path methods in java.lang.String.</div><div style="clear: both;"><br ></div><div style="clear: both;">Performance</div><div style="clear: both;">-----------</div><div style="clear: both;">Benchmarks show 2.6x - 4.3x speedup for common patterns:</div><div style="clear: both;"> "Hello %s".formatted(name) -> 3.75x faster</div><div style="clear: both;"> "%s: %d".formatted(key, value) -> 2.62x faster</div><div style="clear: both;"> "%s %s %s %s".formatted(...) -> 2.68x faster</div><div style="clear: both;"><br ></div><div style="clear: both;">Fallback</div><div style="clear: both;">--------</div><div style="clear: both;">The optimization only applies to simple cases. Complex format strings (width > 9, precision, most flags, non-constant format) fall back to the existing Formatter implementation.</div><div style="clear: both;"><br ></div><div style="clear: both;">Testing</div><div style="clear: both;">-------</div><div style="clear: both;">- JMH microbenchmarks verify performance improvement</div><div style="clear: both;">- jtreg functional tests cover optimized and fallback paths</div><div style="clear: both;">- IR tests verify correct C2 code generation</div><div style="clear: both;"><br ></div><div style="clear: both;">I would appreciate any feedback on the approach or implementation.</div><div style="clear: both;"><br ></div><div style="clear: both;">Thanks,</div><span >Wenshao</span></div></div></div>