Perf: typed int **105 / pow(n,105) chained smul omit llvm.pow.f64 (#36386)

[PurHur]

Summary

• Part of Performance: v2.0 targets and the codegen roadmap to reach them — typed code ≥ 3x Zend, untyped ≤ 1.5x slower, web request ≥ php-fpm: inline caches for property/method access, escape analysis for arrays/strings, guarded speculation, per-function O1 by default (lib/JIT.php, lib/JIT/Builtin/Type/Object_.php, lib/JIT/Analyzer.php) #36386 (lane C; north-star CI: php-llvm-structgep-assert.patch fails to apply — blocks north-star5-verify-fast and all bootstrap gates #36143–VM: 1M-iteration loops exit 255 silently — restore compute-suite headroom on bin/vm.php #36148 closed — lane overflow / Focus: typed fast paths).
• Typed int **105 / pow(n,105) → chained smul.with.overflow (hundredfourth×n) in JitPowIntegerEmitHigh; omit llvm.pow.f64.
• Odd exponent: (-1)**105 === -1. Append-only (no new spine TU).
• php-src: Zend/zend_operators.c pow_function / zend_pow / mul_function; ext/standard/math.c PHP_FUNCTION(pow).

Test plan

• ./script/phpunit.sh --filter NoThrowPowHundredfifthMulAotTest → OK (4 tests, 23 assertions)
• script/differential-sweep.sh --aot --repeat 3 --dir test/differential/cases/_agent_pow105 → 1/1 match Zend (3/3 runs) — case dir cleaned after
• ./script/aot-smoke.sh → 9/9 + size gate OK
• php script/check-size-budgets.php (Docker) → OK
• ./script/opcode-corpus-md5.sh --check (Docker) → OK

Closes: n/a (Part of #36386)

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