Status Update
Comments
rk...@google.com <rk...@google.com>
tn...@google.com <tn...@google.com> #2
Thank you for the report and reproduction. I can reproduce on a Android TV emulator.
an...@steadfastinnovation.com <an...@steadfastinnovation.com> #3
Status of current findings.
This is related to the SplitReturnRewriter
added in
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 {})
.
sg...@google.com <sg...@google.com> #4
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?) {}
tn...@google.com <tn...@google.com> #5
The underlying issue is that branch simplification (as part of dead code removal) is comparing return values through their aliased values (in valuesAreIdentical
) potentially conflating return values with different assume instructions. As this happens before collecting optimization info this can lead to the wrong dynamic type for the return value.
private boolean valuesAreIdentical(Value value, Value other) {
value = value.getAliasedValue();
other = other.getAliasedValue();
if (value == other) {
return true;
}
if (value.isPhi() || other.isPhi()) {
return false;
}
return instructionsDefineIdenticalValues(value.definition, other.definition);
}
tn...@google.com <tn...@google.com> #6
Project: r8
Branch: main
Author: Søren Gjesse <
Link:
Add reproduction of
Expand for full commit details
Add reproduction of b/395489597
Bug: b/395489597
Change-Id: If769fae5db93ee8e2cfc1cf9feeddd847b00832b
Files:
- A
src/test/java/com/android/tools/r8/deadcode/DifferentAssumptionsOnReturnValuesTest.java
Hash: 92f532e6521e5e18a35f365824ad402acb325b3e
Date: Wed Feb 12 12:02:20 2025
an...@google.com <an...@google.com> #7
Project: r8
Branch: main
Author: Søren Gjesse <
Link:
Don't use aliased values when comparing values for basic block subsumption
Expand for full commit details
Don't use aliased values when comparing values for basic block subsumption
Aliased values can be defined by semantically different assume instructions and then the resulting value chosen can have
information which does not correctly represent both values.
Fixes: b/395489597
Change-Id: Ieaeb4fbf8d49cdc60d2912791cc2b701d42d2b34
Files:
- M
src/main/java/com/android/tools/r8/ir/analysis/equivalence/BasicBlockBehavioralSubsumption.java
- M
src/test/java/com/android/tools/r8/deadcode/DifferentAssumptionsOnReturnValuesTest.java
Hash: 94489e15f0c4d1477fe0b16912f6f3bfa4957f09
Date: Wed Feb 12 13:21:29 2025
Description
java.nio
APIs can be used below API 26 withcoreLibraryDesugaring "com.android.tools:desugar_jdk_libs_nio:2.1.3"
. However, as described in thejava.nio
customizations documentationFor example, running the following on API 21 produces a
java.lang.UnsupportedOperationException
:This is expected per the documentation, but is not discoverable except at runtime.
However, when using
coreLibraryDesugaring "com.android.tools:desugar_jdk_libs:2.1.3"
(the non-nio artifact), usages of this API (and all otherjava.nio
APIs) produce lint errors unless wrapped in checks for API 26+.Is it possible to show lint errors just for the APIs that will fail at runtime when they're not wrapped in API checks for API 26+ when using
desugar_jdk_libs_nio
? That way the build will fail rather than discovering this at runtime.