low.scf.while

← low dialect

Condition-controlled target-low loop with explicit condition and body regions. Initial registers and low.scf.yield define the condition-region header tuple. low.scf.condition defines an independent body/result tuple: its forwarded registers enter the body on the true edge and become loop results on the false edge. The tuples may differ in count and register type, and either tuple may be empty.

Operation contract

Property	Value
Semantic phase	executable
Traits	StorageRelation
Interfaces	LoopLike

Signature

Kind	Name	Type	Cardinality	Description
Operand	iter_args	register	variadic	Initial registers for the condition-region header tuple.
Result	results	register	variadic	Registers forwarded by the final false low.scf.condition edge.
Region	before	region	required	Runs before each condition check. Its arguments are initialized by iter_args and updated by low.scf.yield. Terminated by low.scf.condition. (single block, terminator low.scf.condition.)
Region	after	region	required	Runs while the condition is true. Its arguments are the registers forwarded by low.scf.condition. Terminated by low.scf.yield, whose values update the condition-region arguments. (single block, terminator low.scf.yield.)

Verification constraints

• ConditionForwardedCountMatchesBlockArgs(before, after, results)
• ConditionForwardedTypesMatchBlockArgs(before, after, results)
• YieldCountMatches(after, before)
• YieldTypesMatch(after, before)

Examples

low.scf.while {
  low.scf.condition %condition : reg<spirv.id : i1>
} do {
  low.scf.yield
}

%terminal, %candidate = low.scf.while(%before = %initial : reg<spirv.id : i32>) -> (reg<spirv.id : i32>, reg<spirv.id : i32>) {
  %next = OpIAdd %before, %one
  %keep_going = OpULessThan %next, %limit
  low.scf.condition %keep_going, %before, %next : reg<spirv.id : i1>, reg<spirv.id : i32>, reg<spirv.id : i32>
} do(%body_state: reg<spirv.id : i32>, %body_candidate: reg<spirv.id : i32>) {
  low.scf.yield %body_candidate : reg<spirv.id : i32>
}