[llvm] r323320 - [X86][SSE] Avoid calls to combineX86ShufflesRecursively that can't combine to target shuffles (PR32037)

[Simon Pilgrim via llvm-commits]

Author: rksimon
Date: Wed Jan 24 03:41:09 2018
New Revision: 323320

URL: http://llvm.org/viewvc/llvm-project?rev=323320&view=rev
Log:
[X86][SSE] Avoid calls to combineX86ShufflesRecursively that can't combine to target shuffles (PR32037)

Don't bother making recursive calls to combineX86ShufflesRecursively if we have more shuffle source operands than will be combined together with the remaining recursive depth.

See https://bugs.llvm.org/show_bug.cgi?id=32037#c26 and https://bugs.llvm.org/show_bug.cgi?id=32037#c27 for the reduction in compile times from this patch.

Differential Revision: https://reviews.llvm.org/D42378

Modified:
    llvm/trunk/lib/Target/X86/X86ISelLowering.cpp

Modified: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86ISelLowering.cpp?rev=323320&r1=323319&r2=323320&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp Wed Jan 24 03:41:09 2018
@@ -29369,12 +29369,13 @@ static SDValue combineX86ShufflesConstan
 /// combining in this recursive walk.
 static SDValue combineX86ShufflesRecursively(
     ArrayRef<SDValue> SrcOps, int SrcOpIndex, SDValue Root,
-    ArrayRef<int> RootMask, ArrayRef<const SDNode *> SrcNodes, int Depth,
+    ArrayRef<int> RootMask, ArrayRef<const SDNode *> SrcNodes, unsigned Depth,
     bool HasVariableMask, SelectionDAG &DAG,
     TargetLowering::DAGCombinerInfo &DCI, const X86Subtarget &Subtarget) {
   // Bound the depth of our recursive combine because this is ultimately
   // quadratic in nature.
-  if (Depth > 8)
+  const unsigned MaxRecursionDepth = 8;
+  if (Depth > MaxRecursionDepth)
     return SDValue();
 
   // Directly rip through bitcasts to find the underlying operand.
@@ -29527,13 +29528,17 @@ static SDValue combineX86ShufflesRecursi
   // See if we can recurse into each shuffle source op (if it's a target
   // shuffle). The source op should only be combined if it either has a
   // single use (i.e. current Op) or all its users have already been combined.
-  for (int i = 0, e = Ops.size(); i < e; ++i)
-    if (Ops[i].getNode()->hasOneUse() ||
-        SDNode::areOnlyUsersOf(CombinedNodes, Ops[i].getNode()))
-      if (SDValue Res = combineX86ShufflesRecursively(
-              Ops, i, Root, Mask, CombinedNodes, Depth + 1, HasVariableMask,
-              DAG, DCI, Subtarget))
-        return Res;
+  // Don't recurse if we already have more source ops than we can combine in
+  // the remaining recursion depth.
+  if (Ops.size() < (MaxRecursionDepth - Depth)) {
+    for (int i = 0, e = Ops.size(); i < e; ++i)
+      if (Ops[i].getNode()->hasOneUse() ||
+          SDNode::areOnlyUsersOf(CombinedNodes, Ops[i].getNode()))
+        if (SDValue Res = combineX86ShufflesRecursively(
+                Ops, i, Root, Mask, CombinedNodes, Depth + 1, HasVariableMask,
+                DAG, DCI, Subtarget))
+          return Res;
+  }
 
   // Attempt to constant fold all of the constant source ops.
   if (SDValue Cst = combineX86ShufflesConstants(