[llvm] Patch tryCanonicalizeStructToVector to handle split slice tails (PR #201434)

[Yaxun Liu via llvm-commits]

================
@@ -5131,20 +5131,27 @@ static FixedVectorType *tryCanonicalizeStructToVector(StructType *STy,
   if (StructSize != VectorSize)
     return nullptr;
 
-  for (const Slice &S : P) {
+  auto IsMemIntrinsicOnlySlice = [](const Slice &S) {
     if (S.isDead())
-      continue;
+      return true;
     auto *U = S.getUse();
     if (!U)
-      continue;
+      return true;
 
     User *Usr = U->getUser();
     if (isa<LifetimeIntrinsic>(Usr) || isa<DbgInfoIntrinsic>(Usr))
-      continue;
+      return true;
 
-    if (!isa<MemIntrinsic>(Usr))
+    return isa<MemIntrinsic>(Usr);
+  };
+
+  for (const Slice &S : P)
+    if (!IsMemIntrinsicOnlySlice(S))
+      return nullptr;
+
----------------
yxsamliu wrote:

The comment above says "all users of the alloca", but this check is partition-local: it accepts the conversion when all users overlapping this partition are mem/lifetime/debug-like. Maybe clarify that wording now that split tails are part of the check.

https://github.com/llvm/llvm-project/pull/201434