Check for kernel chaining in ScriptGroup

b/21958851

bcc expects kernels chained up via input and output.
Check this in the runtime before passing ScriptGroup to bcc for
compiler fusion.

This serves the same purpose as
https://googleplex-android-review.git.corp.google.com/#/c/713267, but
provides additional checks in the runtime before bcc is even called.

Change-Id: I6004d577410ea1684f5043babadc1e1b885c4f6a
(cherry picked from commit 08e7693c13f895677b93537af3b6bc353318a81c)

1 files changed, 20 insertions, 1 deletions

diff --git a/cpu_ref/rsCpuScriptGroup2.cpp b/cpu_ref/rsCpuScriptGroup2.cpp
index b1453110..8923c651 100644
--- a/cpu_ref/rsCpuScriptGroup2.cpp
+++ b/cpu_ref/rsCpuScriptGroup2.cpp
@@ -128,7 +128,26 @@ bool Batch::conflict(CPUClosure* cpuClosure) const {
         }
     }
 
-    return false;
+    // The compiler fusion pass in bcc expects that kernels chained up through
+    // (1st) input and output.
+
+    const Closure* lastBatched = mClosures.back()->mClosure;
+    const auto& it = argDeps.find(lastBatched);
+
+    if (it == argDeps.end()) {
+        return true;
+    }
+
+    const auto& args = (*it).second;
+    for (const auto &p1 : *args) {
+        if (p1.first == 0 && p1.second.get() == nullptr) {
+            // The new closure depends on the last batched closure's return
+            // value (fieldId being nullptr) for its first argument (argument 0)
+            return false;
+        }
+    }
+
+    return true;
 }
 
 CpuScriptGroup2Impl::CpuScriptGroup2Impl(RsdCpuReferenceImpl *cpuRefImpl,