ffi: preserve uint8 semantics for bool fast calls

[trivikr]

Fixes: #64526

node:ffi documents bool as an 8-bit unsigned integer, but the Fast
API path mapped it to V8's Boolean type. As a result, behavior changed
after JIT optimization:

• return values changed from numbers to JavaScript Booleans;
• true and false became accepted as arguments.

This change normalizes bool to the existing kUint8 Fast FFI type and
removes the now-unused kBool type. The regression test forces V8
optimization and verifies that numeric return values and argument
validation remain consistent.

---

Assisted-by: openai:gpt-5.6-sol

[nodejs-github-bot]

Review requested:

• @nodejs/ffi
• @nodejs/tsc

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.25%. Comparing base (f2ba101) to head (ae0ca8d).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/ffi/fast.cc	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #64527      +/-   ##
==========================================
- Coverage   92.01%   90.25%   -1.77%     
==========================================
  Files         379      739     +360     
  Lines      170129   241649   +71520     
  Branches    26090    45542   +19452     
==========================================
+ Hits       156544   218098   +61554     
- Misses      13293    15093    +1800     
- Partials      292     8458    +8166     

Files with missing lines	Coverage Δ
src/ffi/fast.h	100.00% <ø> (ø)
src/ffi/platforms/arm64.cc	86.90% <ø> (ø)
src/ffi/fast.cc	66.66% <0.00%> (ø)

... and 481 files with indirect coverage changes

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[ShogunPanda]

Can you please run comparison benchmarks to make sure nothing regresses?

[trivikr]

Can you please run comparison benchmarks to make sure nothing regresses?

Did you mean benchmark-node-micro-benchmarks?

[ShogunPanda]

No, I meant something like:

./node-new --no-warnings --experimental-ffi benchmark/compare.js --old ./node-old --new ./node-new --runs 30 --no-progress ffi > compare.csv

And then

npx node-benchmark-compare compare.csv

Note that you need to compile Node twice, once before and once after your changes.

[trivikr]

Benchmark output for add-u8 which this PR touches

                         confidence improvement accuracy (*)   (**)  (***)
ffi/add-u8.js n=10000000                 0.75 %       ±1.47% ±1.95% ±2.54%

[ShogunPanda]

Do you mind posting the entire benchmark? I just want to make sure there are not regressions elsewhere.

[trivikr]

Full ffi benchmarks (separate run)

                                                    confidence improvement accuracy (*)   (**)  (***)
ffi/add-64.js n=10000000                                           -0.16 %       ±0.55% ±0.73% ±0.95%
ffi/add-f32.js n=10000000                                          -0.23 %       ±1.33% ±1.77% ±2.31%
ffi/add-f64.js n=10000000                                          -0.60 %       ±4.27% ±5.68% ±7.41%
ffi/add-i16.js n=10000000                                           0.67 %       ±0.98% ±1.30% ±1.69%
ffi/add-i32.js n=10000000                                           0.57 %       ±5.02% ±6.68% ±8.71%
ffi/add-i64.js n=10000000                                           0.41 %       ±2.46% ±3.28% ±4.27%
ffi/add-i8.js n=10000000                                            0.19 %       ±1.52% ±2.03% ±2.66%
ffi/add-u16.js n=10000000                                          -0.14 %       ±4.44% ±5.92% ±7.71%
ffi/add-u64.js n=10000000                                          -1.19 %       ±2.27% ±3.04% ±4.01%
ffi/add-u8.js n=10000000                                           -0.54 %       ±1.31% ±1.75% ±2.29%
ffi/buffer-first-byte-direct.js n=10000000                         -0.00 %       ±0.25% ±0.33% ±0.43%
ffi/buffer-first-byte.js n=10000000                                 0.46 %       ±1.59% ±2.11% ±2.75%
ffi/buffer-sum-direct.js n=10000000                                 1.45 %       ±2.17% ±2.91% ±3.82%
ffi/buffer-sum.js n=10000000                                        0.67 %       ±2.53% ±3.38% ±4.42%
ffi/getpid.js n=10000000                                           -2.12 %       ±3.19% ±4.30% ±5.70%
ffi/identity-i32.js n=10000000                                      0.33 %       ±0.70% ±0.93% ±1.21%
ffi/many-args.js n=10000000                                        -0.04 %       ±1.01% ±1.34% ±1.75%
ffi/noop-void.js n=10000000                                        -0.97 %       ±4.20% ±5.62% ±7.40%
ffi/pointer-bigint.js n=10000000                                    1.13 %       ±2.46% ±3.31% ±4.38%
ffi/pointer-buffer-direct.js n=10000000                            -0.08 %       ±0.66% ±0.88% ±1.14%
ffi/pointer-buffer.js n=10000000                                    0.32 %       ±1.20% ±1.62% ±2.13%
ffi/pointer-null.js n=10000000                                      0.34 %       ±1.24% ±1.65% ±2.15%
ffi/string-equals-hello-buffer-direct.js n=10000000                -0.23 %       ±0.34% ±0.45% ±0.59%
ffi/string-equals-hello-buffer.js n=10000000                       -0.78 %       ±2.22% ±2.96% ±3.86%
ffi/string-first-char-buffer-direct.js n=10000000                  -0.41 %       ±0.88% ±1.17% ±1.54%
ffi/string-first-char-buffer.js n=10000000                         -1.13 %       ±1.18% ±1.57% ±2.04%
ffi/string-length-buffer-direct.js n=10000000                      -1.36 %       ±2.46% ±3.31% ±4.37%
ffi/string-length-buffer.js n=10000000                              0.00 %       ±0.35% ±0.46% ±0.60%
ffi/string-length-string-direct.js n=10000000                       0.04 %       ±0.11% ±0.15% ±0.20%
ffi/string-length-string.js n=10000000                             -1.15 %       ±1.92% ±2.55% ±3.33%
ffi/sum-3-i32.js n=10000000                                         0.53 %       ±0.81% ±1.07% ±1.40%
ffi/sum-5-i32.js n=10000000                                         0.13 %       ±0.83% ±1.10% ±1.44%
ffi/sum-8-i32.js n=10000000                                         0.24 %       ±0.35% ±0.46% ±0.60%
ffi/sum-buffer.js n=1000000 size=1024                              -1.05 %       ±2.21% ±2.96% ±3.89%
ffi/sum-buffer.js n=1000000 size=16384                             -0.13 %       ±1.25% ±1.66% ±2.17%
ffi/sum-buffer.js n=1000000 size=64                                 1.87 %       ±5.15% ±6.92% ±9.15%