RFR: 8341696: C2: Non-fluid StringBuilder pattern bails out in OptoStringConcat [v5]

[Vladimir Kozlov]

On Fri, 10 Jan 2025 09:37:04 GMT, Theo Weidmann <tweidmann at openjdk.org> wrote:

>> Extends stringopts to also recognize non-fluid uses of StringBuilder and optimize them the same way.
>> 
>> For example, this basic case was not optimized before and is optimized with this PR:
>> 
>> 
>> StringBuilder sb = new StringBuilder();
>> sb.append("a");
>> sb.append(a);
>> return sb.toString();
>
> Theo Weidmann has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Make code more clear

src/hotspot/share/opto/stringopts.cpp line 659:

> 657:           cnode->in(TypeFunc::Parms + 1)->dump();
> 658:         }
> 659: #endif

This print code could be put into `process_append_candidate()` too as you do for `AbortOptimization`.

src/hotspot/share/opto/stringopts.hpp line 58:

> 56:   enum class ProcessAppendResult {
> 57:     // Indicates that the candidate was indeed an append and process_append_candidate processed it
> 58:     // accordingly (added it to the StringCocat etc.)

`StringCocat` -> `StringConcat`

src/hotspot/share/opto/stringopts.hpp line 67:

> 65:   };
> 66: 
> 67:   // Called from build_candidate. Looks at an "append candidate", a call that might be a call to StringBuilder::append. If so, adds it to the StringConcat.

Please split line.

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PR Review Comment: https://git.openjdk.org/jdk/pull/22537#discussion_r1919082945
PR Review Comment: https://git.openjdk.org/jdk/pull/22537#discussion_r1919068910
PR Review Comment: https://git.openjdk.org/jdk/pull/22537#discussion_r1919069842