inlining: allow callsite inlining with cached results

In some rare cases with callsite inlining, we try to inline an inferred
result from a local cache (`inf_result::InferenceResult`), whose source
has been transformed by `transform_result_for_cache`. At present,
`inf_result.src` stays to be `OptimizationState` in such cases,
causing `inlining_policy` to handle the callsite inlining.

This commit adjusts `transform_result_for_cache` so that it stores the
transformed source in `inf_result.src`, letting the callsite inliner
use it. Down the line, we might revisit this change to align it with
532125d, which isn't enabled yet.

base/compiler/typeinfer.jl

@@ -369,10 +369,9 @@ end
 function transform_result_for_cache(interp::AbstractInterpreter,
     linfo::MethodInstance, valid_worlds::WorldRange, result::InferenceResult)
     inferred_result = result.src
-    # If we decided not to optimize, drop the OptimizationState now.
-    # External interpreters can override as necessary to cache additional information
     if inferred_result isa OptimizationState{typeof(interp)}
-        inferred_result = ir_to_codeinf!(inferred_result)
+        # TODO respect must_be_codeinf setting here?
+        result.src = inferred_result = ir_to_codeinf!(inferred_result)
     end
     if inferred_result isa CodeInfo
         inferred_result.min_world = first(valid_worlds)

test/compiler/inline.jl

@@ -705,6 +705,14 @@ mktempdir() do dir
     end
 end
 
+# callsite inlining with cached frames
+issue49823_events = @NamedTuple{evid::Int8, base_time::Float64}[
+    (evid = 1, base_time = 0.0), (evid = -1, base_time = 0.0)]
+issue49823(t, events) = @inline findlast(x -> x.evid ∈ (1, 4) && x.base_time <= t, events)
+let src = @code_typed1 issue49823(0.0, issue49823_events)
+    @test count(isinvoke(:findlast), src.code) == 0 # successful inlining
+end
+
 # Issue #42264 - crash on certain union splits
 let f(x) = (x...,)
     # Test splatting with a Union of non-{Tuple, SimpleVector} types that require creating new `iterate` calls