[PATCH] D53289: [DAGCombiner] Limit the number of chains in findBetterChains().

[Clement Courbet via Phabricator via llvm-commits]

courbet updated this revision to Diff 169705.
courbet added a comment.

revert formatting changes


Repository:
  rL LLVM

https://reviews.llvm.org/D53289

Files:
  include/llvm/CodeGen/TargetLowering.h
  lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  lib/CodeGen/TargetLoweringBase.cpp


Index: lib/CodeGen/TargetLoweringBase.cpp
===================================================================
--- lib/CodeGen/TargetLoweringBase.cpp
+++ lib/CodeGen/TargetLoweringBase.cpp
@@ -558,6 +558,7 @@
   PrefFunctionAlignment = 0;
   PrefLoopAlignment = 0;
   GatherAllAliasesMaxDepth = 18;
+  FindBetterChainsMaxChains = 32;
   MinStackArgumentAlignment = 1;
   // TODO: the default will be switched to 0 in the next commit, along
   // with the Target-specific changes necessary.
Index: lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -17394,7 +17394,7 @@
           NewMask.push_back(M < 0 ? -1 : Scale * M + s);
       return NewMask;
     };
-    
+
     SDValue BC0 = peekThroughOneUseBitcasts(N0);
     if (BC0.getOpcode() == ISD::VECTOR_SHUFFLE && BC0.hasOneUse()) {
       EVT SVT = VT.getScalarType();
@@ -18946,8 +18946,9 @@
 
   // Walk up the chain and look for nodes with offsets from the same
   // base pointer. Stop when reaching an instruction with a different kind
-  // or instruction which has a different base pointer.
+  // or instruction or a different base pointer.
   StoreSDNode *Index = St;
+  const unsigned MaxChains = TLI.getFindBetterChainsMaxChains();
   while (Index) {
     // If the chain has more than one use, then we can't reorder the mem ops.
     if (Index != St && !SDValue(Index, 0)->hasOneUse())
@@ -18974,7 +18975,8 @@
           break;
         }
         ChainedStores.push_back(STn);
-        Index = STn;
+        // Stop if we have too many chains.
+        Index = ChainedStores.size() >= MaxChains ? nullptr : STn;
         break;
       } else if (LoadSDNode *Ldn = dyn_cast<LoadSDNode>(NextInChain)) {
         NextInChain = Ldn->getChain().getNode();
Index: include/llvm/CodeGen/TargetLowering.h
===================================================================
--- include/llvm/CodeGen/TargetLowering.h
+++ include/llvm/CodeGen/TargetLowering.h
@@ -1235,6 +1235,10 @@
     return GatherAllAliasesMaxDepth;
   }
 
+  unsigned getFindBetterChainsMaxChains() const {
+    return FindBetterChainsMaxChains;
+  }
+
   /// Returns the size of the platform's va_list object.
   virtual unsigned getVaListSizeInBits(const DataLayout &DL) const {
     return getPointerTy(DL).getSizeInBits();
@@ -2585,6 +2589,14 @@
   /// expected to be merged.
   unsigned GatherAllAliasesMaxDepth;
 
+  // Number of chains that are considered when looking back for mergeable stores
+  // in DAGCombiner::findBetterNeighborChains. This should be larger than the
+  // maximum number of stores to be merged for a target (e.g. setting this to
+  // 8 will allow merging 8 consecutive i8 stores to one i64). Increasing this
+  // value further will allow discovering and merging potentially
+  // non-consecutive stores to be merged.
+  unsigned FindBetterChainsMaxChains;
+
   /// Specify maximum number of store instructions per memset call.
   ///
   /// When lowering \@llvm.memset this field specifies the maximum number of


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D53289.169705.patch
Type: text/x-patch
Size: 3121 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20181015/24113907/attachment-0001.bin>