[llvm] 1f006f5 - [DAG] mergeTruncStores - early out if we collect more than the maximum number of stores

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2023-06-23T16:22:11+01:00
New Revision: 1f006f5fb63df4facb2c45511090b3fdd3e07de5

URL: https://github.com/llvm/llvm-project/commit/1f006f5fb63df4facb2c45511090b3fdd3e07de5
DIFF: https://github.com/llvm/llvm-project/commit/1f006f5fb63df4facb2c45511090b3fdd3e07de5.diff

LOG: [DAG] mergeTruncStores - early out if we collect more than the maximum number of stores

If we have an excessive number of stores in a single chain then the candidate WideVT may exceed the maximum width of an EVT integer type (and will assert) - but since mergeTruncStores doesn't support anything wider than a i64 store we should just early-out if we've collected more than stores than that.

Fixes #63306

Added: 
    

Modified: 
    llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

Removed: 
    


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diff  --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 77b05a3a12cea..ab36d22a2fb43 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -8679,9 +8679,12 @@ SDValue DAGCombiner::mergeTruncStores(StoreSDNode *N) {
       !N->isSimple() || N->isIndexed())
     return SDValue();
 
-  // Collect all of the stores in the chain.
+  // Collect all of the stores in the chain, upto the maximum store width (i64).
   SDValue Chain = N->getChain();
   SmallVector<StoreSDNode *, 8> Stores = {N};
+  unsigned NarrowNumBits = MemVT.getScalarSizeInBits();
+  unsigned MaxWideNumBits = 64;
+  unsigned MaxStores = MaxWideNumBits / NarrowNumBits;
   while (auto *Store = dyn_cast<StoreSDNode>(Chain)) {
     // All stores must be the same size to ensure that we are writing all of the
     // bytes in the wide value.
@@ -8695,6 +8698,8 @@ SDValue DAGCombiner::mergeTruncStores(StoreSDNode *N) {
       return SDValue();
     Stores.push_back(Store);
     Chain = Store->getChain();
+    if (MaxStores < Stores.size())
+      return SDValue();
   }
   // There is no reason to continue if we do not have at least a pair of stores.
   if (Stores.size() < 2)
@@ -8703,7 +8708,6 @@ SDValue DAGCombiner::mergeTruncStores(StoreSDNode *N) {
   // Handle simple types only.
   LLVMContext &Context = *DAG.getContext();
   unsigned NumStores = Stores.size();
-  unsigned NarrowNumBits = N->getMemoryVT().getScalarSizeInBits();
   unsigned WideNumBits = NumStores * NarrowNumBits;
   EVT WideVT = EVT::getIntegerVT(Context, WideNumBits);
   if (WideVT != MVT::i16 && WideVT != MVT::i32 && WideVT != MVT::i64)