JIT: Don't move EH entry block to enable branch reversal during flow opts (#117618)

Fixes #117581.

Author: amanasifkhalid

src/coreclr/jit/compiler.h

@@ -6153,8 +6153,6 @@ class Compiler
 
     bool fgExpandRarelyRunBlocks();
 
-    bool fgEhAllowsMoveBlock(BasicBlock* bBefore, BasicBlock* bAfter);
-
     void fgMoveBlocksAfter(BasicBlock* bStart, BasicBlock* bEnd, BasicBlock* insertAfterBlk);
 
     PhaseStatus fgHeadTailMerge(bool early);

src/coreclr/jit/fgbasic.cpp

@@ -5309,18 +5309,6 @@ bool Compiler::fgIsForwardBranch(BasicBlock* bJump, BasicBlock* bDest, BasicBloc
     return result;
 }
 
-/*****************************************************************************
- *
- *  Returns true if it is allowable (based upon the EH regions)
- *  to place block bAfter immediately after bBefore. It is allowable
- *  if the 'bBefore' and 'bAfter' blocks are in the exact same EH region.
- */
-
-bool Compiler::fgEhAllowsMoveBlock(BasicBlock* bBefore, BasicBlock* bAfter)
-{
-    return BasicBlock::sameEHRegion(bBefore, bAfter);
-}
-
 /*****************************************************************************
  *
  *  Function called to move the range of blocks [bStart .. bEnd].

src/coreclr/jit/fgopt.cpp

@@ -4517,8 +4517,10 @@ bool Compiler::fgUpdateFlowGraph(bool doTailDuplication /* = false */, bool isPh
                     {
                         // In the join free case, we also need to move bDest right after bNext
                         // to create same flow as in the isJumpAroundEmpty case.
+                        // However, we cannot move bDest if it will break EH invariants.
                         //
-                        if (!fgEhAllowsMoveBlock(bNext, bDest) || bDest->isBBCallFinallyPair())
+                        if (!BasicBlock::sameEHRegion(bNext, bDest) || bbIsTryBeg(bDest) || bbIsHandlerBeg(bDest) ||
+                            bDest->isBBCallFinallyPair())
                         {
                             optimizeJump = false;
                         }