[PATCH] D63948: [SLP] Limit compilation time of look-ahead operand reordering heuristic.

[Vasileios Porpodas via Phabricator via llvm-commits]

vporpo updated this revision to Diff 207177.
vporpo added a comment.

Updated option variable names.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D63948/new/

https://reviews.llvm.org/D63948

Files:
  llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp


Index: llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -153,6 +153,21 @@
     "slp-max-look-ahead-depth", cl::init(2), cl::Hidden,
     cl::desc("The maximum look-ahead depth for operand reordering scores"));
 
+// Look-ahead explores the operands of the bundle. To avoid compilation time
+// increase we limit the number of operands visited to this value.
+static cl::opt<unsigned> LookAheadOperandsBudget(
+    "slp-look-ahead-operands-budget", cl::init(2), cl::Hidden,
+    cl::desc("The maximum number of operands to consider while visiting the "
+             "predecessors. This prevents compilation time increase"));
+
+// Look-ahead goes through the users ot the bundle to calculate the users cost
+// in getExternalUsesCost(). To avoid compilation time increase we limit the
+// number of users visited to this value.
+static cl::opt<unsigned> LookAheadUsersBudget(
+    "slp-look-ahead-users-budget", cl::init(2), cl::Hidden,
+    cl::desc("The maximum number of users to visit while visiting the "
+             "predecessors. This prevents compilation time increase."));
+
 static cl::opt<bool>
     ViewSLPTree("view-slp-tree", cl::Hidden,
                 cl::desc("Display the SLP trees with Graphviz"));
@@ -817,6 +832,7 @@
         // and RHS as base and Idx as the offset.
         int Ln = std::min(LHS.second, RHS.second) + Idx;
         assert(Ln >= 0 && "Bad lane calculation");
+        unsigned UsersBudget = LookAheadUsersBudget;
         for (User *U : V->users()) {
           if (const TreeEntry *UserTE = R.getTreeEntry(U)) {
             // The user is in the VectorizableTree. Check if we need to insert.
@@ -838,6 +854,9 @@
               Cost += ExternalUseCost;
             }
           }
+          // Limit the number of visited uses to cap compilation time.
+          if (--UsersBudget == 0)
+            break;
         }
       }
       return Cost;
@@ -898,7 +917,9 @@
 
       // Recursion towards the operands of I1 and I2. We are trying all possbile
       // operand pairs, and keeping track of the best score.
-      for (unsigned OpIdx1 = 0, NumOperands1 = I1->getNumOperands();
+      for (unsigned OpIdx1 = 0,
+                    NumOperands1 = std::min(I1->getNumOperands(),
+                                            LookAheadOperandsBudget.getValue());
            OpIdx1 != NumOperands1; ++OpIdx1) {
         // Try to pair op1I with the best operand of I2.
         int MaxTmpScore = 0;
@@ -906,8 +927,10 @@
         bool FoundBest = false;
         // If I2 is commutative try all combinations.
         unsigned FromIdx = isCommutative(I2) ? 0 : OpIdx1;
+        // Limit the number of operands to visit to reduce compilation time.
         unsigned ToIdx = isCommutative(I2)
-                             ? I2->getNumOperands()
+                             ? std::min(I2->getNumOperands(),
+                                        LookAheadOperandsBudget.getValue())
                              : std::min(I2->getNumOperands(), OpIdx1 + 1);
         assert(FromIdx <= ToIdx && "Bad index");
         for (unsigned OpIdx2 = FromIdx; OpIdx2 != ToIdx; ++OpIdx2) {


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