V4: do not run optimizer for functions of >300 statements.

The time it takes to run the optimizer depends on both the number of
IR statements, and the number of basic-blocks. Many functions that have
more than 300 statements are either the %entry point, or methods that
set a large number of member variables. Both are not performance
sensitive, so skipping them won't hurt execution speed. Actually,
not optimizing them does improve startup speed.

Basic blocks need to contain at least one statement (the terminator),
so a large number basic blocks always results in at least an equal
number of IR statements. Therefore they do not need to be taken into
account. (An example of an excessive amount of basic blocks is a
switch with 9000 cases: this will generate ~27000 basic blocks.)

Change-Id: Iabf809d8ad293f4f27ece06d136aa281991a1b0f
Reviewed-by: Frank Meerkoetter <frank.meerkoetter@basyskom.com>
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/src/qml/compiler/qv4ssa.cpp b/src/qml/compiler/qv4ssa.cpp
index 449caeebb5..89101ad756 100644
--- a/src/qml/compiler/qv4ssa.cpp
+++ b/src/qml/compiler/qv4ssa.cpp
@@ -5195,12 +5195,15 @@ void Optimizer::run(QQmlEnginePrivate *qmlEngine, bool doTypeInference, bool pee
     cleanupBasicBlocks(function);
 
     function->removeSharedExpressions();
-
+    int statementCount = 0;
+    foreach (BasicBlock *bb, function->basicBlocks())
+        if (!bb->isRemoved())
+            statementCount += bb->statementCount();
 //    showMeTheCode(function);
 
     static bool doSSA = qEnvironmentVariableIsEmpty("QV4_NO_SSA");
 
-    if (!function->hasTry && !function->hasWith && !function->module->debugMode && doSSA) {
+    if (!function->hasTry && !function->hasWith && !function->module->debugMode && doSSA && statementCount <= 300) {
 //        qout << "SSA for " << (function->name ? qPrintable(*function->name) : "<anonymous>") << endl;
 
         ConvertArgLocals(function).toTemps();