[DAGCombine] Fix TypeSize warning in DAGCombine::visitLIFETIME_END

[joechrisellis]

Summary

Bail out early if we encounter a scalable store.

[peterwaller-arm]

LGTM.

[joechrisellis]

Clearer comment.

[joechrisellis]

Accidentally changed the wrong comment in the last update. Corrected.

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

case ISD::LIFETIME_END:
       if (!isAlias(Chain.getNode(), N))
         Chains.push_back(Chain.getOperand(0));
       break;
     case ISD::STORE: {
       StoreSDNode *ST = dyn_cast<StoreSDNode>(Chain);
       // TODO: Can relax for unordered atomics (see D66309)
       if (!ST->isSimple() || ST->isIndexed())
         continue;
+      const TypeSize StoreSize = ST->getMemoryVT().getStoreSize();
+      // The bounds of a scalable store are not known until runtime, so this
+      // store cannot be elided.
+      if (StoreSize.isScalable())
+        continue;
       const BaseIndexOffset StoreBase = BaseIndexOffset::match(ST, DAG);
       // If we store purely within object bounds just before its lifetime ends,
       // we can remove the store.
       if (LifetimeEndBase.contains(DAG, LifetimeEnd->getSize() * 8, StoreBase,
-                                   ST->getMemoryVT().getStoreSizeInBits())) {
+                                   StoreSize.getFixedSize() * 8)) {
         LLVM_DEBUG(dbgs() << "\nRemoving store:"; StoreBase.dump();
                    dbgs() << "\nwithin LIFETIME_END of : ";
                    LifetimeEndBase.dump(); dbgs() << "\n");
         CombineTo(ST, ST->getChain());
         return SDValue(N, 0);
       }
     }
     }

llvm/test/CodeGen/AArch64/dag-combine-lifetime-end-store-typesize.ll

+; RUN: llc -mtriple=aarch64-- < %s 2>&1 | FileCheck --allow-empty %s
+
+; This regression test is defending against a TypeSize warning 'assumption that TypeSize is not
+; scalable'. This warning appeared in DAGCombiner::visitLIFETIME_END when visiting a LIFETIME_END
+; node linked to a scalable store.
+
+; If this check fails please read test/CodeGen/AArch64/README for instructions on how to resolve it.
+; CHECK-NOT: warning: {{.*}}TypeSize is not scalable
+
+declare void @llvm.lifetime.start.p0i8(i64, i8* nocapture)
+declare void @llvm.lifetime.end.p0i8(i64, i8* nocapture)
+
+define void @foo(<vscale x 4 x i32>* nocapture dereferenceable(16) %ptr) {
+entry:
+  %tmp = alloca <vscale x 4 x i32>, align 8
+  %tmp_ptr = bitcast <vscale x 4 x i32>* %tmp to i8*
+  call void @llvm.lifetime.start.p0i8(i64 32, i8* %tmp_ptr)
+  store <vscale x 4 x i32> undef, <vscale x 4 x i32>* %ptr
+  call void @llvm.lifetime.end.p0i8(i64 32, i8* %tmp_ptr)
+  ret void
+}