RFR: 8280526: x86_32 Math.sqrt performance regression with -XX:UseSSE={0,1}

[Aleksey Shipilev]

See more details in the bug.

x86_32 performance:


# ---- Before JDK-8279076

# -XX:UseAVX=0 -XX:UseSSE=0
MathBench.sqrtDouble       0  thrpt    8  406540.546 ± 2299.428  ops/ms

# -XX:UseAVX=0 -XX:UseSSE=1
MathBench.sqrtDouble       0  thrpt    8  408018.332 ± 1423.456  ops/ms

# ---- Current mainline

# -XX:UseAVX=0 -XX:UseSSE=0
MathBench.sqrtDouble       0  thrpt    8    9983.414 ± 426.007  ops/ms

# -XX:UseAVX=0 -XX:UseSSE=1
MathBench.sqrtDouble       0  thrpt    8    9883.518 ± 513.648  ops/ms

# ---- Patched 

# -XX:UseAVX=0 -XX:UseSSE=0
MathBench.sqrtDouble       0  thrpt    8  407267.348 ± 1605.200  ops/ms

# -XX:UseAVX=0 -XX:UseSSE=1
MathBench.sqrtDouble       0  thrpt    8  407500.560 ± 739.249  ops/ms


While this is technically a regression in JDK 18, this is an edge case, so I would bring it to 18.0.1, instead of going into JDK 18 RDP2 process.

Additional testing:
 - [x] Linux x86_64 `compiler/c2/TestSqrt.java` with `-XX:UseAVX=0 -XX:UseSSE=2`
 - [x] Linux x86_32 `compiler/c2/TestSqrt.java` with `-XX:UseAVX=0 -XX:UseSSE=0`
 - [x] Linux x86_32 `compiler/c2/TestSqrt.java` with `-XX:UseAVX=0 -XX:UseSSE=1`
 - [x] Linux x86_32 `compiler/c2/TestSqrt.java` with `-XX:UseAVX=0 -XX:UseSSE=2`
 - [x] Linux x86_32 `compiler/loopopts/superword/SumRedSqrt_Double.java` with `-XX:UseAVX=0 -XX:UseSSE=0`
 - [x] Linux x86_32 `compiler/loopopts/superword/SumRedSqrt_Double.java` with `-XX:UseAVX=0 -XX:UseSSE=1`
 - [x] Linux x86_32 `compiler/loopopts/superword/SumRedSqrt_Double.java` with `-XX:UseAVX=0 -XX:UseSSE=2`
 - [ ] Linux x86_32 `tier1` with `-XX:UseAVX=0 -XX:UseSSE=0`
 - [ ] Linux x86_32 `tier1` with `-XX:UseAVX=0 -XX:UseSSE=1`

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

Commit messages:
 - Fix

Changes: https://git.openjdk.java.net/jdk/pull/7200/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7200&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8280526
  Stats: 5 lines in 1 file changed: 5 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7200.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7200/head:pull/7200

PR: https://git.openjdk.java.net/jdk/pull/7200