Trace profiling on Pixel 8 revealed two massive overhead sources:
1. ExternalSyntheticBackport0.m — 17.5% of verify (3.45ms)
D8/R8 desugaring wraps Math.unsignedMultiplyHigh in a synthetic
backport because minSdk=26 < 35. The backport adds 139ns per call
× 24,875 calls. The actual UMULH intrinsic is ~1ns, but the
wrapper adds ~138ns.
FIX: Use pure-Kotlin unsignedMultiplyHighFallback on Android instead
of Math.unsignedMultiplyHigh. The fallback (4 Long multiplies +
shifts, ~10-20ns) is FASTER than the backported intrinsic (139ns).
Removed all API-level dispatch — a single fallback path for all
Android versions.
2. uLt function calls — 20.7% of verify (4.08ms)
The expect/actual uLt (can't be inline) was called 49,924 times
per verify at 82ns each. Most calls came from the fused
fieldMulReduceWith/fieldSqrReduceWith inline expansions.
FIX: Add uLtInline — a private inline function using the XOR trick
directly. Since it's @Suppress("NOTHING_TO_INLINE") inline, the
Kotlin compiler inlines it at every call site (not the JIT).
Replaces all 55 uLt calls in the fused inline functions.
JVM is unaffected (uses unfused path with Long.compareUnsigned).
Combined: eliminates ~38% of verify overhead on Android.
https://claude.ai/code/session_01EMY5RnXb9rnsyU2KbXrSaY
Claude
c243e3894c