[llvm] [SLP]Improve minbitwidth analysis. (PR #78976)

[Simon Pilgrim via llvm-commits]

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@@ -13270,171 +13305,253 @@ bool BoUpSLP::collectValuesToDemote(
   case Instruction::PHI: {
     PHINode *PN = cast<PHINode>(I);
     for (Value *IncValue : PN->incoming_values())
-      if (!collectValuesToDemote(IncValue, ToDemote, DemotedConsts, Roots,
-                                 Visited))
+      if (!collectValuesToDemote(IncValue, IsProfitableToDemoteRoot, BitWidth,
+                                 ToDemote, DemotedConsts, Visited,
+                                 MaxDepthLevel, IsProfitableToDemote))
         return false;
     break;
   }
 
   // Otherwise, conservatively give up.
   default:
-    return false;
+    if (!IsPotentiallyTruncated(I, BitWidth))
+      return false;
+    MaxDepthLevel = 0;
+    Start = End = 0;
+    break;
   }
 
+  ++MaxDepthLevel;
   // Gather demoted constant operands.
   for (unsigned Idx : seq<unsigned>(Start, End))
     if (isa<Constant>(I->getOperand(Idx)))
       DemotedConsts.try_emplace(I).first->getSecond().push_back(Idx);
   // Record the value that we can demote.
   ToDemote.push_back(V);
-  return true;
+  return IsProfitableToDemote;
 }
 
 void BoUpSLP::computeMinimumValueSizes() {
   // We only attempt to truncate integer expressions.
-  auto &TreeRoot = VectorizableTree[0]->Scalars;
-  auto *TreeRootIT = dyn_cast<IntegerType>(TreeRoot[0]->getType());
-  if (!TreeRootIT || VectorizableTree.front()->State == TreeEntry::NeedToGather)
-    return;
+  bool IsStoreOrInsertElt =
+      VectorizableTree.front()->getOpcode() == Instruction::Store ||
+      VectorizableTree.front()->getOpcode() == Instruction::InsertElement;
+  unsigned NodeIdx = 0;
+  if (IsStoreOrInsertElt &&
+      VectorizableTree.front()->State != TreeEntry::NeedToGather)
+    NodeIdx = 1;
 
   // Ensure the roots of the vectorizable tree don't form a cycle.
-  if (!VectorizableTree.front()->UserTreeIndices.empty())
+  if (VectorizableTree[NodeIdx]->State == TreeEntry::NeedToGather ||
+      (NodeIdx == 0 && !VectorizableTree[NodeIdx]->UserTreeIndices.empty()) ||
+      (NodeIdx != 0 && any_of(VectorizableTree[NodeIdx]->UserTreeIndices,
+                              [&](const EdgeInfo &EI) {
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RKSimon wrote:

`[&]` -> `[NodeIdx]` ? Do we need full capture?

https://github.com/llvm/llvm-project/pull/78976