JIT: allow some aggressive inlines to go over budget

If we have a very small root method that calls a large method that is marked with
AggressiveInlining, we may fail to inline because of a budget check.

Allow such inlines to bypass the check.

Closes dotnet#38106.

src/coreclr/src/jit/inline.cpp

@@ -1151,8 +1151,16 @@ void InlineStrategy::NoteOutcome(InlineContext* context)
 
 bool InlineStrategy::BudgetCheck(unsigned ilSize)
 {
-    int timeDelta = EstimateInlineTime(ilSize);
-    return (timeDelta + m_CurrentTimeEstimate > m_CurrentTimeBudget);
+    const int  timeDelta = EstimateInlineTime(ilSize);
+    const bool result    = (timeDelta + m_CurrentTimeEstimate > m_CurrentTimeBudget);
+
+    if (result)
+    {
+        JITDUMP("\nBudgetCheck: for IL Size %d, timeDelta %d +  currentEstimate %d > currentBudget %d\n", ilSize,
+                timeDelta, m_CurrentTimeEstimate, m_CurrentTimeBudget);
+    }
+
+    return result;
 }
 
 //------------------------------------------------------------------------

src/coreclr/src/jit/inlinepolicy.cpp

@@ -369,14 +369,33 @@ void DefaultPolicy::NoteBool(InlineObservation obs, bool value)
                 // the candidate IL size during the inlining pass it
                 // "reestablishes" candidacy rather than alters
                 // candidacy ... so instead we bail out here.
-
+                //
                 if (!m_IsPrejitRoot)
                 {
                     InlineStrategy* strategy   = m_RootCompiler->m_inlineStrategy;
-                    bool            overBudget = strategy->BudgetCheck(m_CodeSize);
+                    const bool      overBudget = strategy->BudgetCheck(m_CodeSize);
+
                     if (overBudget)
                     {
-                        SetFailure(InlineObservation::CALLSITE_OVER_BUDGET);
+                        // If the candidate is a forceinline and the callsite is
+                        // not too deep, allow the inline even if it goes over budget.
+                        //
+                        // For now, "not too deep" means a top-level inline. Note
+                        // depth 0 is used for the root method, so inline candiate depth
+                        // will be 1 or more.
+                        //
+                        assert(m_IsForceInlineKnown);
+                        assert(m_CallsiteDepth > 0);
+                        const bool allowOverBudget = m_IsForceInline && (m_CallsiteDepth == 1);
+
+                        if (allowOverBudget)
+                        {
+                            JITDUMP("Allowing over-budget top-level forceinline\n");
+                        }
+                        else
+                        {
+                            SetFailure(InlineObservation::CALLSITE_OVER_BUDGET);
+                        }
                     }
                 }
 
@@ -531,9 +550,9 @@ void DefaultPolicy::NoteInt(InlineObservation obs, int value)
 
         case InlineObservation::CALLSITE_DEPTH:
         {
-            unsigned depth = static_cast<unsigned>(value);
+            m_CallsiteDepth = static_cast<unsigned>(value);
 
-            if (depth > m_RootCompiler->m_inlineStrategy->GetMaxInlineDepth())
+            if (m_CallsiteDepth > m_RootCompiler->m_inlineStrategy->GetMaxInlineDepth())
             {
                 SetFailure(InlineObservation::CALLSITE_IS_TOO_DEEP);
             }
@@ -1858,6 +1877,7 @@ void DiscretionaryPolicy::DumpSchema(FILE* file) const
     fprintf(file, ",CallerHasNewObj");
     fprintf(file, ",CalleeDoesNotReturn");
     fprintf(file, ",CalleeHasGCStruct");
+    fprintf(file, ",CallsiteDepth");
 }
 
 //------------------------------------------------------------------------
@@ -1940,6 +1960,7 @@ void DiscretionaryPolicy::DumpData(FILE* file) const
     fprintf(file, ",%u", m_CallerHasNewObj ? 1 : 0);
     fprintf(file, ",%u", m_IsNoReturn ? 1 : 0);
     fprintf(file, ",%u", m_CalleeHasGCStruct ? 1 : 0);
+    fprintf(file, ",%u", m_CallsiteDepth);
 }
 
 #endif // defined(DEBUG) || defined(INLINE_DATA)

src/coreclr/src/jit/inlinepolicy.h

@@ -89,6 +89,7 @@ class DefaultPolicy : public LegalPolicy
         , m_Multiplier(0.0)
         , m_CodeSize(0)
         , m_CallsiteFrequency(InlineCallsiteFrequency::UNUSED)
+        , m_CallsiteDepth(0)
         , m_InstructionCount(0)
         , m_LoadStoreCount(0)
         , m_ArgFeedsTest(0)
@@ -154,6 +155,7 @@ class DefaultPolicy : public LegalPolicy
     double                  m_Multiplier;
     unsigned                m_CodeSize;
     InlineCallsiteFrequency m_CallsiteFrequency;
+    unsigned                m_CallsiteDepth;
     unsigned                m_InstructionCount;
     unsigned                m_LoadStoreCount;
     unsigned                m_ArgFeedsTest;