JIT: refactor instrumentation code (#47509)

Refactor `fgInstrument` and related methods and classes, so that the strategies
for block and class instrumentation are clearly separated out, and can be
varied.

src/coreclr/jit/block.h

@@ -726,8 +726,16 @@ struct BasicBlock : private LIR::Range
     };
 
 #define NO_BASE_TMP UINT_MAX // base# to use when we have none
-    unsigned bbStkTempsIn;   // base# for input stack temps
-    unsigned bbStkTempsOut;  // base# for output stack temps
+
+    union {
+        unsigned bbStkTempsIn;       // base# for input stack temps
+        int      bbCountSchemaIndex; // schema index for count instrumentation
+    };
+
+    union {
+        unsigned bbStkTempsOut;      // base# for output stack temps
+        int      bbClassSchemaIndex; // schema index for class instrumentation
+    };
 
 #define MAX_XCPTN_INDEX (USHRT_MAX - 1)
 

src/coreclr/jit/compiler.h

@@ -5586,15 +5586,14 @@ class Compiler
 #endif
 
 public:
+    Statement* fgNewStmtAtBeg(BasicBlock* block, GenTree* tree);
     void fgInsertStmtAtEnd(BasicBlock* block, Statement* stmt);
     Statement* fgNewStmtAtEnd(BasicBlock* block, GenTree* tree);
     Statement* fgNewStmtNearEnd(BasicBlock* block, GenTree* tree);
 
 private:
     void fgInsertStmtNearEnd(BasicBlock* block, Statement* stmt);
     void fgInsertStmtAtBeg(BasicBlock* block, Statement* stmt);
-    Statement* fgNewStmtAtBeg(BasicBlock* block, GenTree* tree);
-
     void fgInsertStmtAfter(BasicBlock* block, Statement* insertionPoint, Statement* stmt);
 
 public:

src/coreclr/jit/compmemkind.h

@@ -58,6 +58,7 @@ CompMemKindMacro(ClassLayout)
 CompMemKindMacro(TailMergeThrows)
 CompMemKindMacro(EarlyProp)
 CompMemKindMacro(ZeroInit)
+CompMemKindMacro(Pgo)
 //clang-format on
 
 #undef CompMemKindMacro