IncrementalCompact: fix stateful behavior when using multiple iterators.

Author: maleadt

base/compiler/ssair/ir.jl

@@ -1421,7 +1421,8 @@ function iterate(it::CompactPeekIterator, (idx, aidx, bidx)::NTuple{3, Int}=(it.
 end
 
 # This Union{Nothing, Pair{Pair{Int,Int},Any}} cannot be stack allocated, so we inline it
-@inline function iterate(compact::IncrementalCompact, st::Tuple{Int, Int}=(compact.idx, 1))
+@inline function iterate(compact::IncrementalCompact,
+                         st::Tuple{Int, Int}=(compact.idx, compact.active_result_bb))
     st = iterate_compact(compact, st)
     st === nothing && return nothing
     old_result_idx = st[1][2]

test/compiler/ssair.jl

@@ -461,3 +461,24 @@ let ir = Base.code_ircode((Bool,Any)) do c, x
         end
     end
 end
+
+@testset "IncrementalCompact statefulness" begin
+    foo(i) = i == 1 ? 1 : 2
+    ir = only(Base.code_ircode(foo, (Int,)))[1]
+    compact = Core.Compiler.IncrementalCompact(ir)
+
+    # set up first iterator
+    x = Core.Compiler.iterate(compact)
+    x = Core.Compiler.iterate(compact, x[2])
+
+    # set up second iterator
+    x = Core.Compiler.iterate(compact)
+
+    # consume remainder
+    while x !== nothing
+        x = Core.Compiler.iterate(compact, x[2])
+    end
+
+    ir = Core.Compiler.complete(compact)
+    @test Core.Compiler.verify_ir(ir) === nothing
+end