JIT: Copy BBF_ASYNC_RESUMPTION when splitting edges in LSRA (#115836)

Async resumption BBs are introduced late enough that we allow them to do
some things that general BBs are not allowed to do. For example, they
are allowed to jump into try regions at any point. This allowance is
marked with the `BBF_ASYNC_RESUMPTION` flag. Propagate this flag from
the source when edges are split by LSRA to allow the new block the same
affordances.

Author: jakobbotsch

src/coreclr/jit/fgbasic.cpp

@@ -4968,6 +4968,10 @@ BasicBlock* Compiler::fgSplitEdge(BasicBlock* curr, BasicBlock* succ)
     }
     newBlock->CopyFlags(curr, succ->GetFlagsRaw() & BBF_BACKWARD_JUMP);
 
+    // Async resumption stubs are permitted to branch into EH regions, so if we
+    // split such a branch we should also copy this flag.
+    newBlock->CopyFlags(curr, BBF_ASYNC_RESUMPTION);
+
     JITDUMP("Splitting edge from " FMT_BB " to " FMT_BB "; adding " FMT_BB "\n", curr->bbNum, succ->bbNum,
             newBlock->bbNum);
 

src/coreclr/jit/fgdiagnostic.cpp

@@ -2714,7 +2714,7 @@ bool BBPredsChecker::CheckEhTryDsc(BasicBlock* block, BasicBlock* blockPred, EHb
         return true;
     }
 
-    printf("Jump into the middle of try region: " FMT_BB " branches to " FMT_BB "\n", blockPred->bbNum, block->bbNum);
+    JITDUMP("Jump into the middle of try region: " FMT_BB " branches to " FMT_BB "\n", blockPred->bbNum, block->bbNum);
     assert(!"Jump into middle of try region");
     return false;
 }
@@ -2746,8 +2746,8 @@ bool BBPredsChecker::CheckEhHndDsc(BasicBlock* block, BasicBlock* blockPred, EHb
         return true;
     }
 
-    printf("Jump into the middle of handler region: " FMT_BB " branches to " FMT_BB "\n", blockPred->bbNum,
-           block->bbNum);
+    JITDUMP("Jump into the middle of handler region: " FMT_BB " branches to " FMT_BB "\n", blockPred->bbNum,
+            block->bbNum);
     assert(!"Jump into the middle of handler region");
     return false;
 }