Never set fgPgoSingleEdge for cctors or large single-edge blocks (#117420)

Author: EgorBo

src/coreclr/jit/compiler.cpp

@@ -2550,8 +2550,9 @@ void Compiler::compInitOptions(JitFlags* jitFlags)
     opts.genFPorder = true;
     opts.genFPopt   = true;
 
-    opts.instrCount = 0;
-    opts.lvRefCount = 0;
+    opts.instrCount     = 0;
+    opts.callInstrCount = 0;
+    opts.lvRefCount     = 0;
 
 #ifdef PROFILING_SUPPORTED
     opts.compJitELTHookEnabled = false;

src/coreclr/jit/compiler.h

@@ -9913,8 +9913,9 @@ class Compiler
             compSupportsISA = isas;
         }
 
-        unsigned compFlags; // method attributes
-        unsigned instrCount = 0;
+        unsigned compFlags;          // method attributes
+        unsigned instrCount     = 0; // number of IL opcodes
+        unsigned callInstrCount = 0; // number of IL opcodes (calls only).
         unsigned lvRefCount;
 
         codeOptimize compCodeOpt; // what type of code optimizations

src/coreclr/jit/fgbasic.cpp

@@ -3170,6 +3170,7 @@ void Compiler::fgMakeBasicBlocks(const BYTE* codeAddr, IL_OFFSET codeSize, Fixed
             case CEE_CALLVIRT:
             case CEE_CALLI:
             {
+                opts.callInstrCount++;
                 if (compIsForInlining() ||               // Ignore tail call in the inlinee. Period.
                     (!tailCall && !compTailCallStress()) // A new BB with BBJ_RETURN would have been created
 
@@ -3288,6 +3289,7 @@ void Compiler::fgMakeBasicBlocks(const BYTE* codeAddr, IL_OFFSET codeSize, Fixed
 
             // These ctrl-flow opcodes don't need any special handling
             case CEE_NEWOBJ: // CTRL_CALL
+                opts.callInstrCount++;
                 break;
 
             // what's left are forgotten instructions

src/coreclr/jit/fgprofilesynthesis.cpp

@@ -249,14 +249,23 @@ void ProfileSynthesis::Run(ProfileSynthesisOption option)
     m_comp->fgPgoSynthesized = true;
     m_comp->fgPgoConsistent  = !m_approximate;
 
-    // A simple check whether the current method has more than one edge.
-    m_comp->fgPgoSingleEdge = true;
-    for (BasicBlock* const block : m_comp->Blocks())
+    // If a method has just one edge, we simulate having PGO data for it since we typically
+    // don't instrument such methods. To avoid giving excessive inlining boost to large and/or
+    // infrequently executed methods, we apply the following heuristics to exclude:
+    //
+    const bool preferSize   = m_comp->opts.jitFlags->IsSet(JitFlags::JIT_FLAG_SIZE_OPT);
+    const bool isCctor      = (m_comp->info.compFlags & FLG_CCTOR) == FLG_CCTOR;
+    m_comp->fgPgoSingleEdge = !isCctor && !preferSize && (m_comp->opts.callInstrCount < 10);
+
+    if (m_comp->fgPgoSingleEdge)
     {
-        if (block->NumSucc() > 1)
+        for (BasicBlock* const block : m_comp->Blocks())
         {
-            m_comp->fgPgoSingleEdge = false;
-            break;
+            if (block->NumSucc() > 1)
+            {
+                m_comp->fgPgoSingleEdge = false;
+                break;
+            }
         }
     }
 

src/coreclr/jit/jit.h

@@ -738,16 +738,9 @@ inline size_t unsigned_abs(int64_t x)
 #define FEATURE_TAILCALL_OPT_SHARED_RETURN 0
 #endif // !FEATURE_TAILCALL_OPT
 
-#define CLFLG_CODESIZE   0x00001
-#define CLFLG_CODESPEED  0x00002
-#define CLFLG_CSE        0x00004
-#define CLFLG_REGVAR     0x00008
-#define CLFLG_RNGCHKOPT  0x00010
-#define CLFLG_DEADSTORE  0x00020
-#define CLFLG_CODEMOTION 0x00040
-#define CLFLG_QMARK      0x00080
-#define CLFLG_TREETRANS  0x00100
-#define CLFLG_INLINING   0x00200
+#define CLFLG_REGVAR    0x00008
+#define CLFLG_TREETRANS 0x00100
+#define CLFLG_INLINING  0x00200
 
 #if FEATURE_STRUCTPROMOTE
 #define CLFLG_STRUCTPROMOTE 0x00400
@@ -761,10 +754,7 @@ inline size_t unsigned_abs(int64_t x)
 #define FEATURE_LOOP_ALIGN 0
 #endif
 
-#define CLFLG_MAXOPT                                                                                                   \
-    (CLFLG_CSE | CLFLG_REGVAR | CLFLG_RNGCHKOPT | CLFLG_DEADSTORE | CLFLG_CODEMOTION | CLFLG_QMARK | CLFLG_TREETRANS | \
-     CLFLG_INLINING | CLFLG_STRUCTPROMOTE)
-
+#define CLFLG_MAXOPT (CLFLG_REGVAR | CLFLG_TREETRANS | CLFLG_INLINING | CLFLG_STRUCTPROMOTE)
 #define CLFLG_MINOPT (CLFLG_TREETRANS)
 
 /*****************************************************************************/