JIT: Specialize fgFindJumpTargets (#103761)

This specializes `fgFindJumpTargets` based on whether we are making
inline observations or not. This function has a lot of conditional logic
based on this property, but it is always going to be false in MinOpts,
so this allows the native compiler to optimize the function much better
(and avoids all the conditionals).

Using the VS profiler shows that the relative CPU time spent in the
function goes from 0.98% to 0.47% for the MinOpts contexts in
benchmarks.run_pgo.windows.x64.

src/coreclr/jit/compiler.h

@@ -6315,6 +6315,7 @@ class Compiler
 
     bool fgMayExplicitTailCall();
 
+    template<bool makeInlineObservations>
     void fgFindJumpTargets(const BYTE* codeAddr, IL_OFFSET codeSize, FixedBitVect* jumpTarget);
 
     void fgMarkBackwardJump(BasicBlock* startBlock, BasicBlock* endBlock);

src/coreclr/jit/fgbasic.cpp

@@ -1064,13 +1064,16 @@ class FgStack
 //------------------------------------------------------------------------
 // fgFindJumpTargets: walk the IL stream, determining jump target offsets
 //
+// Type arguments:
+//   makeInlineObservations - whether or not to record inline observations about the method
+//
 // Arguments:
 //    codeAddr   - base address of the IL code buffer
 //    codeSize   - number of bytes in the IL code buffer
 //    jumpTarget - [OUT] bit vector for flagging jump targets
 //
 // Notes:
-//    If inlining or prejitting the root, this method also makes
+//    If "makeInlineObservations" is true this method also makes
 //    various observations about the method that factor into inline
 //    decisions.
 //
@@ -1080,6 +1083,7 @@ class FgStack
 //
 //    Also sets m_addrExposed and lvHasILStoreOp, ilHasMultipleILStoreOp in lvaTable[].
 //
+template <bool makeInlineObservations>
 void Compiler::fgFindJumpTargets(const BYTE* codeAddr, IL_OFFSET codeSize, FixedBitVect* jumpTarget)
 {
     const BYTE* codeBegp = codeAddr;
@@ -1088,13 +1092,12 @@ void Compiler::fgFindJumpTargets(const BYTE* codeAddr, IL_OFFSET codeSize, Fixed
     var_types   varType      = DUMMY_INIT(TYP_UNDEF); // TYP_ type
     bool        typeIsNormed = false;
     FgStack     pushedStack;
-    const bool  isForceInline          = (info.compFlags & CORINFO_FLG_FORCEINLINE) != 0;
-    const bool  makeInlineObservations = (compInlineResult != nullptr);
-    const bool  isInlining             = compIsForInlining();
-    unsigned    retBlocks              = 0;
-    int         prefixFlags            = 0;
-    bool        preciseScan            = makeInlineObservations && compInlineResult->GetPolicy()->RequiresPreciseScan();
-    const bool  resolveTokens          = preciseScan;
+    const bool  isForceInline = (info.compFlags & CORINFO_FLG_FORCEINLINE) != 0;
+    const bool  isInlining    = compIsForInlining();
+    unsigned    retBlocks     = 0;
+    int         prefixFlags   = 0;
+    bool        preciseScan   = makeInlineObservations && compInlineResult->GetPolicy()->RequiresPreciseScan();
+    const bool  resolveTokens = preciseScan;
 
     // Track offsets where IL instructions begin in DEBUG builds. Used to
     // validate debug info generated by the JIT.
@@ -3614,7 +3617,14 @@ void Compiler::fgFindBasicBlocks()
     FixedBitVect* jumpTarget = FixedBitVect::bitVectInit(info.compILCodeSize + 1, this);
 
     // Walk the instrs to find all jump targets
-    fgFindJumpTargets(info.compCode, info.compILCodeSize, jumpTarget);
+    if (compInlineResult != nullptr)
+    {
+        fgFindJumpTargets<true>(info.compCode, info.compILCodeSize, jumpTarget);
+    }
+    else
+    {
+        fgFindJumpTargets<false>(info.compCode, info.compILCodeSize, jumpTarget);
+    }
     if (compDonotInline())
     {
         return;