Upstream regression: compiler refuses to convert cint to uint32

[mratsim]

See: https://github.com/mratsim/constantine/actions/runs/11034017591/job/30646539242?pr=468

The flow:

Threadpool has a cint numThreads

constantine/constantine/threadpool/threadpool.nim

Lines 188 to 195 in 65147ed

	Threadpool* = ptr object
	# All synchronization objects are put in their own cache-line to avoid invalidating
	# and reloading cache for immutable fields
	barrier{.align: 64.}: SyncBarrier # Barrier for initialization and teardown
	# -- align: 64
	globalBackoff{.align: 64.}: EventCount # Multi-Producer Multi-Consumer backoff
	# -- align: 64
	numThreads*{.align: 64.}: cint # N regular workers

It is passed to pseudoRandomPermutation which only accepts an uint32

constantine/constantine/threadpool/threadpool.nim

Lines 656 to 667 in 65147ed

	proc tryStealOne(ctx: var WorkerContext): ptr Task =
	## Try to steal a task.
	let seed = ctx.rng.nextU32()
	for targetId in seed.pseudoRandomPermutation(ctx.threadpool.numThreads):
	if targetId == ctx.id:
	continue
	let stolenTask = ctx.id.steal(ctx.threadpool.workerQueues[targetId])
	if not stolenTask.isNil():
	return stolenTask
	return nil

There should be an error but there aren't, I assume because it's an iterator.

The input is cast to uint32

constantine/constantine/threadpool/threadpool.nim

Lines 121 to 122 in 65147ed

	let maxExclusive = cast[uint32](maxExclusive)
	let M = maxExclusive.nextPowerOfTwo_vartime()

And then passed to a function that only accepts unsigned integers with no problem

constantine/constantine/platforms/bithacks.nim

Lines 156 to 159 in 65147ed

	func nextPowerOfTwo_vartime*(n: SomeUnsignedInt): SomeUnsignedInt {.inline.} =
	## Returns x if x is a power of 2
	## or the next biggest power of 2
	1.SomeUnsignedInt shl (log2_vartime(n-1) + 1)

Forwarded to a dispatcher

constantine/constantine/platforms/bithacks.nim

Lines 97 to 105 in 65147ed

	func log2_vartime*[T: SomeUnsignedInt](n: T): T {.inline.} =
	## Find the log base 2 of an integer
	when nimvm:
	when sizeof(T) == 8:
	T(log2_impl_vartime(uint64(n)))
	else:
	T(log2_impl_vartime(uint32(n)))
	else:
	T(log2_c_compiler_vartime(n))

And to the final builtins, depending on Clang/GCC vs ICC/MSVC, the result is a cint that is converted back to T in the previous proc

constantine/constantine/platforms/intrinsics/bitops.nim

Lines 25 to 36 in 65147ed

	func log2_c_compiler_vartime*(n: SomeUnsignedInt): cint {.inline.} =
	## Compute the log2 of n using compiler builtin
	## ⚠ Depending on the compiler:
	## - It is undefined if n == 0
	## - It is not constant-time as a zero input is checked
	if n == 0:
	0
	else:
	when sizeof(n) == 8:
	cint(63) - builtin_clzll(n)
	else:
	cint(31) - builtin_clz(n.uint32)

constantine/constantine/platforms/intrinsics/bitops.nim

Lines 82 to 90 in 65147ed

	func log2_c_compiler_vartime*(n: SomeUnsignedInt): cint {.inline.} =
	## Compute the log2 of n using compiler builtin
	## ⚠ Depending on the compiler:
	## - It is undefined if n == 0
	## - It is not constant-time as a zero input is checked
	when sizeof(n) == 8:
	bitscan(bitScanReverse64, n, default = 0)
	else:
	bitscan(bitScanReverse, c.uint32, default = 0)

Notice the error Error: type mismatch: got 'cint' for 'log2_c_compiler_vartime(n)' but expected 'uint32'

[mratsim]

Actually already fixed in #459 was working on an unsynced master branch.