[SLP] Remove ScheduleData::UnscheduledDepsInBundle field [NFC-ish]

We can simply compute the value of this field on demand.  Doing so clarifies the behavior when one of the instructions within a bundle doesn't have valid dependencies.  I vaguely thing this could change behavior slightly, but none of the test cases are affected, and my attempts to write one by hand have failed.

This also minorly reduces memory usage, but that's a secondary value at best.

Author: preames

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -2456,7 +2456,6 @@ class BoUpSLP {
       NextLoadStore = nullptr;
       IsScheduled = false;
       SchedulingRegionID = BlockSchedulingRegionID;
-      UnscheduledDepsInBundle = UnscheduledDeps;
       clearDependencies();
       OpValue = OpVal;
       TE = nullptr;
@@ -2467,8 +2466,8 @@ class BoUpSLP {
     void verify() {
       if (hasValidDependencies()) {
         assert(UnscheduledDeps <= Dependencies && "invariant");
-        assert(UnscheduledDeps <= FirstInBundle->UnscheduledDepsInBundle &&
-               "bundle must have at least as many dependencies as member");
+      } else {
+        assert(UnscheduledDeps == Dependencies && "invariant");
       }
 
       if (IsScheduled) {
@@ -2479,6 +2478,8 @@ class BoUpSLP {
     }
 
     /// Returns true if the dependency information has been calculated.
+    /// Note that depenendency validity can vary between instructions within
+    /// a single bundle.
     bool hasValidDependencies() const { return Dependencies != InvalidDeps; }
 
     /// Returns true for single instructions and for bundle representatives
@@ -2496,20 +2497,23 @@ class BoUpSLP {
     bool isReady() const {
       assert(isSchedulingEntity() &&
              "can't consider non-scheduling entity for ready list");
-      return UnscheduledDepsInBundle == 0 && !IsScheduled;
+      return unscheduledDepsInBundle() == 0 && !IsScheduled;
     }
 
-    /// Modifies the number of unscheduled dependencies, also updating it for
-    /// the whole bundle.
+    /// Modifies the number of unscheduled dependencies for this instruction,
+    /// and returns the number of remaining dependencies for the containing
+    /// bundle.
     int incrementUnscheduledDeps(int Incr) {
+      assert(hasValidDependencies() &&
+             "increment of unscheduled deps would be meaningless");
       UnscheduledDeps += Incr;
-      return FirstInBundle->UnscheduledDepsInBundle += Incr;
+      return FirstInBundle->unscheduledDepsInBundle();
     }
 
     /// Sets the number of unscheduled dependencies to the number of
     /// dependencies.
     void resetUnscheduledDeps() {
-      incrementUnscheduledDeps(Dependencies - UnscheduledDeps);
+      UnscheduledDeps = Dependencies;
     }
 
     /// Clears all dependency information.
@@ -2519,6 +2523,18 @@ class BoUpSLP {
       MemoryDependencies.clear();
     }
 
+    int unscheduledDepsInBundle() const {
+      assert(isSchedulingEntity() && "only meaningful on the bundle");
+      int Sum = 0;
+      for (const ScheduleData *BundleMember = this; BundleMember;
+           BundleMember = BundleMember->NextInBundle) {
+        if (BundleMember->UnscheduledDeps == InvalidDeps)
+          return InvalidDeps;
+        Sum += BundleMember->UnscheduledDeps;
+      }
+      return Sum;
+    }
+
     void dump(raw_ostream &os) const {
       if (!isSchedulingEntity()) {
         os << "/ " << *Inst;
@@ -2572,10 +2588,6 @@ class BoUpSLP {
     /// Note that this is negative as long as Dependencies is not calculated.
     int UnscheduledDeps = InvalidDeps;
 
-    /// The sum of UnscheduledDeps in a bundle. Equals to UnscheduledDeps for
-    /// single instructions.
-    int UnscheduledDepsInBundle = InvalidDeps;
-
     /// True if this instruction is scheduled (or considered as scheduled in the
     /// dry-run).
     bool IsScheduled = false;
@@ -7503,8 +7515,6 @@ BoUpSLP::BlockScheduling::buildBundle(ArrayRef<Value *> VL) {
     } else {
       Bundle = BundleMember;
     }
-    BundleMember->UnscheduledDepsInBundle = 0;
-    Bundle->UnscheduledDepsInBundle += BundleMember->UnscheduledDeps;
 
     // Group the instructions to a bundle.
     BundleMember->FirstInBundle = Bundle;
@@ -7631,8 +7641,7 @@ void BoUpSLP::BlockScheduling::cancelScheduling(ArrayRef<Value *> VL,
     BundleMember->FirstInBundle = BundleMember;
     ScheduleData *Next = BundleMember->NextInBundle;
     BundleMember->NextInBundle = nullptr;
-    BundleMember->UnscheduledDepsInBundle = BundleMember->UnscheduledDeps;
-    if (BundleMember->UnscheduledDepsInBundle == 0) {
+    if (BundleMember->unscheduledDepsInBundle() == 0) {
       ReadyInsts.insert(BundleMember);
     }
     BundleMember = Next;