[AIEX] Initialize top scoreboard only for the first region

This avoids the creation of empty regions before the epilogue, which can lead
to timing failures related to the pipeline/epilogue relationship.

Author: andcarminati

llvm/lib/Target/AIE/AIEMachineScheduler.cpp

@@ -355,6 +355,14 @@ void AIEPostRASchedStrategy::initializeBotScoreBoard(ScoreboardTrust Trust) {
 
 void AIEPostRASchedStrategy::initializeTopScoreBoard() {
 
+  // Top Scoreboard is only used for Post-SWP epilogue merging.
+  // If we have a multiregion MBB, the epilogue will be scheduled
+  // in the first topological region. In this case, ignore scoreboard
+  // initialization for other regions.
+  const bool IsFirstRegion = DAG->begin() == CurMBB->begin();
+  if (!IsFirstRegion)
+    return;
+
   auto EpilogueContextOpt = InterBlock.getSWPEpilogueContext(CurMBB);
 
   if (!EpilogueContextOpt)

llvm/test/CodeGen/AIE/schedule/sched-initialize-topscb-once.ll

@@ -26,17 +26,7 @@ define void @load_store_with_call() {
 ; CHECK-NEXT:  .L_LEnd0:
 ; CHECK-NEXT:    nopa ; vldb x0, [p5, #0]; vst x0, [p5, #0]; nopxm ; nopv
 ; CHECK-NEXT:  // %bb.2: // %exit
-; CHECK-NEXT:    nop
-; CHECK-NEXT:    nop
-; CHECK-NEXT:    nop
-; CHECK-NEXT:    nop
-; CHECK-NEXT:    nop
-; CHECK-NEXT:    nop
-; CHECK-NEXT:    nop
-; CHECK-NEXT:    nop
-; CHECK-NEXT:    nop
-; CHECK-NEXT:    nop
-; CHECK-NEXT:    vst x0, [p5, #0]
+; CHECK-NEXT:    vst x0, [p5, #0]; nopb ; nopx
 ; CHECK-NEXT:    vst x0, [p5, #0]
 ; CHECK-NEXT:    vst x0, [p5, #0]
 ; CHECK-NEXT:    vst x0, [p5, #0]