[SR-13903] Make `ApplyInst` a `MultipleValueInstruction`
#56.301 aperta il 27 nov 2020
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Descrizione
| Previous ID | SR-13903 |
| Radar | rdar://problem/71913175 |
| Original Reporter | @dan-zheng |
| Type | Improvement |
| Votes | 0 |
| Component/s | Compiler |
| Labels | Improvement, SILOptimizer, StarterBug |
| Assignee | sachinvas16 (JIRA) |
| Priority | Medium |
md5: 41f0f57e0ecea221993e51084b3f1975
Issue Description:
Forum question with context: https://forums.swift.org/t/make-applyinst-a-multiplevalueinstruction/42294
SIL supports instructions that return multiple values (i.e. multiple result {{SILValue}}s).
However, apply instructions don't return multiple values. Instead, they produce a single value, which may have a tuple type. This leads to much avoidable destructuring and restructuring of tuples, which complicates SIL transformations like autodiff:
// example.swift
@_silgen_name("foo")
func foo() -> (Int, Int) {
(0, 0)
}
@_silgen_name("bar")
func bar() -> (Int, Int) {
return foo()
}
$ swiftc -emit-silgen example.swift
sil hidden [ossa] @bar : $@convention(thin) () -> (Int, Int) {
bb0:
%0 = function_ref @foo : $@convention(thin) () -> (Int, Int)
%1 = apply %0() : $@convention(thin) () -> (Int, Int)
(%2, %3) = destructure_tuple %1 : $(Int, Int) // this is not good
%4 = tuple (%2 : $Int, %3 : $Int)
return %4 : $(Int, Int)
}
Instead, we can change ApplyInst to inherit MultipleResultInstruction.
Steps:
1. Change definition: make ApplyInst inherit MultipleValueInstruction.
Fix obvious compilation errors in the compiler codebase. Fix as many tests as possible.
2. Update and fix ApplyInst users: SIL generation + parsing + verification + printing, analyses and transformations, IRGen.