IssueTracker

Thank you for the report and reproduction. I can reproduce on a Android TV emulator.

Status of current findings.

This is related to the SplitReturnRewriter added in https://r8.googlesource.com/r8/+/0c68ba1dc945da74c2f72085b401fe46635b3fc9.

Not running this code pass on java.lang.Object androidx.collection.LruCache.remove(java.lang.Object) works around the issue. I used the following patch:

diff --git a/src/main/java/com/android/tools/r8/ir/conversion/passes/SplitReturnRewriter.java b/src/main/java/com/android/tools/r8/ir/conversion/passes/SplitReturnRewriter.java
index 157d26c66a..63e0f76064 100644
--- a/src/main/java/com/android/tools/r8/ir/conversion/passes/SplitReturnRewriter.java
+++ b/src/main/java/com/android/tools/r8/ir/conversion/passes/SplitReturnRewriter.java
@@ -43,6 +43,10 @@ public class SplitReturnRewriter extends CodeRewriterPass<AppInfo> {
 
   @Override
   protected CodeRewriterResult rewriteCode(IRCode code) {
+    if (code.context().toSourceString().equals(
+        "java.lang.Object androidx.collection.LruCache.remove(java.lang.Object)")) {
+      return CodeRewriterResult.NO_CHANGE;
+    }
     int color = colorExceptionHandlers(code);
     AffectedValues affectedValues = new AffectedValues();
     boolean changed = false;

Comparing the DEX with and without this patch shows one instruction diff in void androidx.leanback.widget.GridLayoutManager$2.addItem(java.lang.Object, int, int, int, int) where java.lang.Object androidx.collection.LruCache.remove(java.lang.Object) is inlined into.

Tracing the IR for void androidx.leanback.widget.GridLayoutManager$2.addItem(java.lang.Object, int, int, int, int) for the two versions shows that they start to deviate in second pass of IR after inserting assume instructions (SSA) with

block 29, pred-counts: 1, succ-count: 2, filled: true, sealed: false
predecessors: 28 
successors: 31 30  (no try/catch successors)
no phis
 #143:loadView;1762:addItem: -1: InstanceGet          v67 <- v136; field: androidx.collection.LruCache androidx.leanback.widget.ViewsStateBundle.mChildStates
                           : -1: Assume               v140 <- v67; lower bound: @Nullable androidx.collection.LruCache {}
                           : -1: SafeCheckCast        v131 <- v65; java.lang.String
                           : -1: Invoke-Virtual       v132 <- v140, v131; method: java.lang.Object androidx.collection.LruCache.remove(java.lang.String)
                           : -1: CheckCast            v69 <- v132; android.util.SparseArray
 #144:loadView;1762:addItem: -1: If                   v69 EQZ block 31 (fallthrough 30)

vs.

block 29, pred-counts: 1, succ-count: 2, filled: true, sealed: false
predecessors: 28 
successors: 31 30  (no try/catch successors)
no phis
 #143:loadView;1762:addItem: -1: InstanceGet          v67 <- v136; field: androidx.collection.LruCache androidx.leanback.widget.ViewsStateBundle.mChildStates
                           : -1: Assume               v140 <- v67; lower bound: @Nullable androidx.collection.LruCache {}
                           : -1: SafeCheckCast        v131 <- v65; java.lang.String
                           : -1: Invoke-Virtual       v132 <- v140, v131; method: java.lang.Object androidx.collection.LruCache.remove(java.lang.String)
                           : -1: Assume               v141 <- v132; not null
                           : -1: CheckCast            v69 <- v141; android.util.SparseArray
 #144:loadView;1762:addItem: -1: If                   v69 EQZ block 31 (fallthrough 30)

This is from computeDynamicReturnType concluding a dynamic return type of DynamicTypeWithUpperBound(@NotNull java.lang.Object {}).

Looks like dead code removal in java.lang.Object androidx.collection.LruCache.remove(java.lang.Object) is causing this.

The method java.lang.Object androidx.collection.LruCache.remove(java.lang.Object) is processed twice in first round of IR, second time with more precise type for the argument as java.lang.Object androidx.collection.LruCache.remove(java.lang.String).

That second processing involves quite a bit of inlining. However before dead code removal the return is still split between null and not null return value:

block 33, pred-counts: 1, succ-count: 2, filled: true, sealed: false
predecessors: 32 
successors: 37 34  (no try/catch successors)
no phis
 #187:remove;0:remove: -1: If                   v54 EQZ block 37 (fallthrough 34)

block 34, pred-counts: 1, succ-count: 1, filled: true, sealed: false
predecessors: 33 
successors: 35  (no try/catch successors)
no phis
 #187:remove;0:remove: -1: Assume               v49 <- v54; not null
 #188:remove;0:remove: -1: ConstNumber          v32(0b0) <-  0 (INT)
                     : -1: ConstNumber          v33(0) <-  0 (@Null NULL)
                     : -1: Goto                 block 35

block 35, pred-counts: 1, succ-count: 0, filled: true, sealed: false
predecessors: 34 
successors: -
no phis
 #188:remove;0:remove: -1: ConstString          v90 <-  "key"
                     : -1: Invoke-Static        v45, v90; method: void kotlin.jvm.internal.Intrinsics.checkNotNullParameter(java.lang.Object, java.lang.String)
                     : -1: ConstString          v91 <-  "oldValue"
                     : -1: Invoke-Static        v49, v91; method: void kotlin.jvm.internal.Intrinsics.checkNotNullParameter(java.lang.Object, java.lang.String)
 #191:remove;0:remove: -1: Return               v49

block 37, pred-counts: 1, succ-count: 0, filled: true, sealed: false
predecessors: 33 
successors: -
no phis
 #191:remove;0:remove: -1: Return               v54

After dead code removal a single return is left with the non null assumption:

block 34, pred-counts: 1, succ-count: 1, filled: true, sealed: false
predecessors: 32 
successors: 35  (no try/catch successors)
no phis
 #187:remove;0:remove: -1: Assume               v49 <- v54; not null
 #188:remove;0:remove: -1: Goto                 block 35

block 35, pred-counts: 1, succ-count: 0, filled: true, sealed: false
predecessors: 34 
successors: -
no phis
 #191:remove;0:remove: -1: Return               v49

For reference the source of the method is:

    public fun remove(key: K): V? {
        val previous: V?
        lock.synchronized {
            previous = map.remove(key)
            if (previous != null) {
                size -= safeSizeOf(key, previous)
            }
        }

        if (previous != null) {
            entryRemoved(false, key, previous, null)
        }

        return previous
    }

with the default implementation of entryRemoved doing nothing:

    protected open fun entryRemoved(evicted: Boolean, key: K, oldValue: V, newValue: V?) {}