Bug 933369 part 1 - Improve heuristics for Ion try-catch compilation. r=bhackett

js/src/jit/Bailouts.cpp

@@ -205,11 +205,6 @@ jit::CheckFrequentBailouts(JSContext *cx, JSScript *script)
 
             if (!Invalidate(cx, script))
                 return false;
-        } else {
-            // If we keep bailing out to handle exceptions, invalidate and
-            // forbid compilation.
-            if (ionScript->numExceptionBailouts() >= js_IonOptions.exceptionBailoutThreshold)
-                ForbidCompilation(cx, script);
         }
     }
 

js/src/jit/BaselineBailouts.cpp

@@ -1244,9 +1244,7 @@ jit::BailoutIonToBaseline(JSContext *cx, JitActivation *activation, IonBailoutIt
     IonSpew(IonSpew_BaselineBailouts, "  Reading from snapshot offset %u size %u",
             iter.snapshotOffset(), iter.ionScript()->snapshotsSize());
 
-    if (excInfo)
+    if (!excInfo)
-        iter.ionScript()->incNumExceptionBailouts();
-    else
         iter.ionScript()->incNumBailouts();
     iter.script()->updateBaselineOrIonRaw();
 

js/src/jit/Ion.cpp

@@ -711,7 +711,6 @@ IonScript::IonScript()
     invalidateEpilogueOffset_(0),
     invalidateEpilogueDataOffset_(0),
     numBailouts_(0),
-    numExceptionBailouts_(0),
     hasUncompiledCallTarget_(false),
     hasSPSInstrumentation_(false),
     runtimeData_(0),

js/src/jit/IonCode.h

@@ -190,10 +190,6 @@ struct IonScript
     // Number of times this script bailed out without invalidation.
     uint32_t numBailouts_;
 
-    // Number of times this scripted bailed out to enter a catch or
-    // finally block.
-    uint32_t numExceptionBailouts_;
-
     // Flag set when it is likely that one of our (transitive) call
     // targets is not compiled.  Used in ForkJoin.cpp to decide when
     // we should add call targets to the worklist.
@@ -412,12 +408,6 @@ struct IonScript
     bool bailoutExpected() const {
         return numBailouts_ > 0;
     }
-    void incNumExceptionBailouts() {
-        numExceptionBailouts_++;
-    }
-    uint32_t numExceptionBailouts() const {
-        return numExceptionBailouts_;
-    }
     void setHasUncompiledCallTarget() {
         hasUncompiledCallTarget_ = true;
     }

js/src/jit/IonFrames.cpp

@@ -363,6 +363,11 @@ HandleExceptionIon(JSContext *cx, const InlineFrameIterator &frame, ResumeFromEx
 
           case JSTRY_CATCH:
             if (cx->isExceptionPending()) {
+                // Ion can compile try-catch, but bailing out to catch
+                // exceptions is slow. Reset the use count so that if we
+                // catch many exceptions we won't Ion-compile the script.
+                script->resetUseCount();
+
                 // Bailout at the start of the catch block.
                 jsbytecode *catchPC = script->main() + tn->start + tn->length;
 
@@ -477,6 +482,11 @@ HandleExceptionBaseline(JSContext *cx, const IonFrameIterator &frame, ResumeFrom
         switch (tn->kind) {
           case JSTRY_CATCH:
             if (cx->isExceptionPending()) {
+                // Ion can compile try-catch, but bailing out to catch
+                // exceptions is slow. Reset the use count so that if we
+                // catch many exceptions we won't Ion-compile the script.
+                script->resetUseCount();
+
                 // Resume at the start of the catch block.
                 rfe->kind = ResumeFromException::RESUME_CATCH;
                 jsbytecode *catchPC = script->main() + tn->start + tn->length;