Inliner: Update data collection by targeting a single inline

The inliner currently will record detailed data about the last successful
inline performed (given a build with DEBUG or INLINE_DATA defined).
However, for purposes of inline profitability analysis we might be more
interested in the data from an earlier inline.

This change creates a mechanism where the replay log can flag one inline
per method as the target of data collection. The inliner checks for this
attribute during replay and captures that inline's data.

Author: AndyAyersMS

src/jit/inline.cpp

@@ -955,8 +955,23 @@ void InlineStrategy::NoteOutcome(InlineContext* context)
 
 #if defined(DEBUG) || defined(INLINE_DATA)
 
-        m_LastContext = context;
-        m_LastSuccessfulPolicy = context->m_Policy;
+        // Keep track of the inline targeted for data collection or,
+        // if we don't have one (yet), the last successful inline.
+        bool updateLast =
+            (m_LastSuccessfulPolicy == nullptr) ||
+            !m_LastSuccessfulPolicy->IsDataCollectionTarget();
+
+        if (updateLast)
+        {
+            m_LastContext = context;
+            m_LastSuccessfulPolicy = context->m_Policy;
+        }
+        else
+        {
+            // We only expect one inline to be a data collection
+            // target.
+            assert(!context->m_Policy->IsDataCollectionTarget());
+        }
 
 #endif // defined(DEBUG) || defined(INLINE_DATA)
 

src/jit/inline.h

@@ -256,6 +256,8 @@ class InlinePolicy
     virtual void DumpData(FILE* file) const { }
     // Detailed data name dump
     virtual void DumpSchema(FILE* file) const { }
+    // True if this is the inline targeted by data collection
+    bool IsDataCollectionTarget() { return m_IsDataCollectionTarget; }
 
 #endif // defined(DEBUG) || defined(INLINE_DATA)
 
@@ -265,6 +267,10 @@ class InlinePolicy
         : m_Decision(InlineDecision::UNDECIDED)
         , m_Observation(InlineObservation::CALLEE_UNUSED_INITIAL)
         , m_IsPrejitRoot(isPrejitRoot)
+#if defined(DEBUG) || defined(INLINE_DATA)
+        , m_IsDataCollectionTarget(false)
+#endif // defined(DEBUG) || defined(INLINE_DATA)
+
     {
         // empty
     }
@@ -280,6 +286,12 @@ class InlinePolicy
     InlineDecision    m_Decision;
     InlineObservation m_Observation;
     bool              m_IsPrejitRoot;
+
+#if defined(DEBUG) || defined(INLINE_DATA)
+
+    bool              m_IsDataCollectionTarget;
+
+#endif // defined(DEBUG) || defined(INLINE_DATA)
 };
 
 // InlineResult summarizes what is known about the viability of a

src/jit/inlinepolicy.cpp

@@ -2038,7 +2038,7 @@ void ModelPolicy::DetermineProfitability(CORINFO_METHOD_INFO* methodInfo)
         // positive be better and negative worse.
         double perCallBenefit = -((double) m_PerCallInstructionEstimate / (double) m_ModelCodeSizeEstimate);
 
-        // Now estimate the local call frequency.  
+        // Now estimate the local call frequency.
         //
         // Todo: use IBC data, or a better local profile estimate, or
         // try and incorporate this into the model. For instance if we
@@ -2072,8 +2072,8 @@ void ModelPolicy::DetermineProfitability(CORINFO_METHOD_INFO* methodInfo)
         // is our benefit figure of merit.
         double benefit = callSiteWeight * perCallBenefit;
 
-        // Compare this to the threshold, and inline if greater.  
-        // 
+        // Compare this to the threshold, and inline if greater.
+        //
         // The threshold is interpretable as a size/speed tradeoff:
         // the value of 0.2 below indicates we'll allow inlines that
         // grow code by as many as 5 bytes to save 1 instruction
@@ -2583,6 +2583,22 @@ bool ReplayPolicy::FindInline(unsigned token, unsigned hash, unsigned offset)
 
         // We're good!
         foundInline = true;
+
+        // Check for a data collection marker. This does not affect
+        // matching...
+
+        // Get next line
+        if (fgets(buffer, sizeof(buffer), s_ReplayFile) != nullptr)
+        {
+            unsigned collectData = 0;
+            count = sscanf(buffer, " <CollectData>%u</CollectData> ", &collectData);
+
+            if (count == 1)
+            {
+                m_IsDataCollectionTarget = (collectData == 1);
+            }
+        }
+
         break;
     }