JDK-8370677 : AArch64: C2 SuperWord: implement sequential reduction for add/mul D/F
  • Type: Enhancement
  • Component: hotspot
  • Sub-Component: compiler
  • Affected Version: 26
  • Priority: P4
  • Status: Open
  • Resolution: Unresolved
  • CPU: aarch64
  • Submitted: 2025-10-27
  • Updated: 2025-10-27
The Version table provides details related to the release that this issue/RFE will be addressed.

Unresolved : Release in which this issue/RFE will be addressed.
Resolved: Release in which this issue/RFE has been resolved.
Fixed : Release in which this issue/RFE has been fixed. The release containing this fix may be available for download as an Early Access Release or a General Availability Release.

To download the current JDK release, click here.
Other
tbdUnresolved
Related Reports
Relates :  
JDK-8340093 - C2 SuperWord: implement cost model
Relates :  
JDK-8370673 - C2 SuperWord [x86]: implement long mul reduction
Relates :  
JDK-8370671 - C2 SuperWord [x86]: implement Long.max/min reduction for AVX2
Description
Found during JDK-8340093.

~/Documents/oracle/jdk-fork6/open/src/hotspot/cpu/aarch64/aarch64_vector.ad
Matcher::match_rule_supported_auto_vectorization

This seems to suggest that we don't want to use the implemented NEON reductions, because they use the recusive fold approach, which creates different errors. But of course, we could just implement a linear reduction.

It also seems that there is no SVE support for linear float reductions, for add/mul on D/F.

However: I'm not sure if that is profitable, probably only in edge cases. Still, I wanted to file this report, just so the issue is recorded.