[llvm] [SandboxVec][Scheduler] Enforce scheduling SchedBundle instrs back-to-back (PR #128092)

[Sriraman Tallam via llvm-commits]

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@@ -125,36 +125,72 @@ SchedBundle *Scheduler::createBundle(ArrayRef<Instruction *> Instrs) {
 void Scheduler::eraseBundle(SchedBundle *SB) { Bndls.erase(SB); }
 
 bool Scheduler::tryScheduleUntil(ArrayRef<Instruction *> Instrs) {
-  // Use a set of instructions, instead of `Instrs` for fast lookups.
-  DenseSet<Instruction *> InstrsToDefer(Instrs.begin(), Instrs.end());
-  // This collects the nodes that correspond to instructions found in `Instrs`
-  // that have just become ready. These nodes won't be scheduled right away.
-  SmallVector<DGNode *, 8> DeferredNodes;
-
+  // Create a bundle for Instrs. If it turns out the schedule is infeasible we
+  // will dismantle it.
+  auto *InstrsSB = createBundle(Instrs);
   // Keep scheduling ready nodes until we either run out of ready nodes (i.e.,
   // ReadyList is empty), or all nodes that correspond to `Instrs` (the nodes of
   // which are collected in DeferredNodes) are all ready to schedule.
-  while (!ReadyList.empty()) {
-    auto *ReadyN = ReadyList.pop();
-    if (InstrsToDefer.contains(ReadyN->getInstruction())) {
-      // If the ready instruction is one of those in `Instrs`, then we don't
-      // schedule it right away. Instead we defer it until we can schedule it
-      // along with the rest of the instructions in `Instrs`, at the same
-      // time in a single scheduling bundle.
-      DeferredNodes.push_back(ReadyN);
-      bool ReadyToScheduleDeferred = DeferredNodes.size() == Instrs.size();
-      if (ReadyToScheduleDeferred) {
-        scheduleAndUpdateReadyList(*createBundle(Instrs));
+  SmallVector<DGNode *> Retry;
+  bool KeepScheduling = true;
+  while (KeepScheduling) {
+    enum class TryScheduleRes {
+      Success, ///> We successfully scheduled the node.
+      Failure, ///> We failed to schedule the node.
+      Done,    ///> We scheduled the `Instrs` bundle.
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tmsri wrote:

What is the difference between Success and Done here?

https://github.com/llvm/llvm-project/pull/128092