From 88b2d88817097bb8a4fe294420ba03b211163ac4 Mon Sep 17 00:00:00 2001
From: Huihong Luo <huisinro@google.com>
Date: Fri, 4 Jun 2021 15:19:38 -0700
Subject: Put debug/log code under verbose flag

So they are not invoked when verbose flag is off:
(1) that the compiler will optimize to strip out no-op loops
(2) statements are put into a local function variable so invoked only with ALOGV.

Bug: 189837811
Test: examine logcat
Change-Id: I00ba0433f47586d8356423b8147cf9786f1045b9
---
 .../CompositionEngine/src/planner/Flattener.cpp     | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/services/surfaceflinger/CompositionEngine/src/planner/Flattener.cpp b/services/surfaceflinger/CompositionEngine/src/planner/Flattener.cpp
index fb24fa4160..550fdebea4 100644
--- a/services/surfaceflinger/CompositionEngine/src/planner/Flattener.cpp
+++ b/services/surfaceflinger/CompositionEngine/src/planner/Flattener.cpp
@@ -231,6 +231,7 @@ bool Flattener::mergeWithCachedSets(const std::vector<const LayerState*>& layers
         return false;
     }
 
+    // the compiler should strip out the following no-op loops when ALOGV is off
     ALOGV("[%s] Incoming layers:", __func__);
     for (const LayerState* layer : layers) {
         ALOGV("%s", layer->getName().c_str());
@@ -238,9 +239,12 @@ bool Flattener::mergeWithCachedSets(const std::vector<const LayerState*>& layers
 
     ALOGV("[%s] Current layers:", __func__);
     for (const CachedSet& layer : mLayers) {
-        std::string dump;
-        layer.dump(dump);
-        ALOGV("%s", dump.c_str());
+        const auto dumper = [&] {
+            std::string dump;
+            layer.dump(dump);
+            return dump;
+        };
+        ALOGV("%s", dumper().c_str());
     }
 
     auto currentLayerIter = mLayers.begin();
@@ -473,9 +477,14 @@ void Flattener::buildCachedSets(time_point now) {
 
     ++mCachedSetCreationCount;
     mCachedSetCreationCost += mNewCachedSet->getCreationCost();
-    std::string setDump;
-    mNewCachedSet->dump(setDump);
-    ALOGV("[%s] Added new cached set:\n%s", __func__, setDump.c_str());
+
+    // note the compiler should strip the follow no-op statements when ALOGV is off
+    const auto dumper = [&] {
+        std::string setDump;
+        mNewCachedSet->dump(setDump);
+        return setDump;
+    };
+    ALOGV("[%s] Added new cached set:\n%s", __func__, dumper().c_str());
 }
 
 } // namespace android::compositionengine::impl::planner
-- 
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