Integrated: 8345766: C2 should emit macro nodes for ModF/ModD instead of calls during parsing

[Theo Weidmann]

On Tue, 17 Dec 2024 09:01:57 GMT, Theo Weidmann <tweidmann at openjdk.org> wrote:

> C2 currently emits runtime calls if the platform rules do not support lowering floating point remainder operations. For example, for float:
> 
> https://github.com/openjdk/jdk/blob/fbbc7c35f422294090b8c7a02a19ab2fb67c7070/src/hotspot/share/opto/parse2.cpp#L2305-L2318
> 
> https://github.com/openjdk/jdk/blob/fbbc7c35f422294090b8c7a02a19ab2fb67c7070/src/hotspot/share/opto/parse2.cpp#L1099-L1109
> 
> The only platform, which currently supports this, however, is x86_32. On all other platforms, runtime calls are generated directly during parsing, which prevent any constant folding or other idealizations. Even C1 can perform these optimizations, resulting in significantly lower C2 performance compared to C1 for simple test cases. This function was observed to be around 15x slower with C2 compared to C1 due to redundant runtime calls:
> 
> 
> public static double process(final double x) {
>         double w = (double) 0.1;
>         double p = 0;
>         p = (double) (3.109615012413746E307 % (w % Z));
>         p = (double) (7.614949555185036E307 / (x % x)); // <- return value only dependends on this line
>         return (double) (x * p);
> }
> 
> 
> To fix this, this PR turns ModFNode and ModDNode into macros, which are always created during parsing. They support idealization (constant folding) and are lowered to runtime calls during macro expansion. For simplicity, these operations will now also call into the runtime on x86_32, as this platform is deprecated.

This pull request has now been integrated.

Changeset: f54e0bf2
Author:    Theo Weidmann <tweidmann at openjdk.org>
Committer: Emanuel Peter <epeter at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/f54e0bf267280c270b0e181289498b28aaf36ee6
Stats:     629 lines in 11 files changed: 359 ins; 206 del; 64 mod

8345766: C2 should emit macro nodes for ModF/ModD instead of calls during parsing

Reviewed-by: kvn, epeter

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PR: https://git.openjdk.org/jdk/pull/22786