[PATCH] D149195: [SelectionDAG] Limit max recursion in `isKnownNeverZero` and `isKnownToBeAPowerOfTwo`

[Noah Goldstein via Phabricator via llvm-commits]

goldstein.w.n updated this revision to Diff 517327.
goldstein.w.n added a comment.

Use `Depth` in all recursive calls


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D149195/new/

https://reviews.llvm.org/D149195

Files:
  llvm/include/llvm/CodeGen/SelectionDAG.h
  llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp


Index: llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -3975,7 +3975,10 @@
   return OFK_Sometime;
 }
 
-bool SelectionDAG::isKnownToBeAPowerOfTwo(SDValue Val) const {
+bool SelectionDAG::isKnownToBeAPowerOfTwo(SDValue Val, unsigned Depth) const {
+  if (Depth++ >= MaxRecursionDepth)
+    return false; // Limit search depth.
+
   EVT OpVT = Val.getValueType();
   unsigned BitWidth = OpVT.getScalarSizeInBits();
 
@@ -4017,14 +4020,14 @@
   // vscale(power-of-two) is a power-of-two for some targets
   if (Val.getOpcode() == ISD::VSCALE &&
       getTargetLoweringInfo().isVScaleKnownToBeAPowerOfTwo() &&
-      isKnownToBeAPowerOfTwo(Val.getOperand(0)))
+      isKnownToBeAPowerOfTwo(Val.getOperand(0), Depth))
     return true;
 
   // More could be done here, though the above checks are enough
   // to handle some common cases.
 
   // Fall back to computeKnownBits to catch other known cases.
-  KnownBits Known = computeKnownBits(Val);
+  KnownBits Known = computeKnownBits(Val, Depth - 1);
   return (Known.countMaxPopulation() == 1) && (Known.countMinPopulation() == 1);
 }
 
@@ -4992,7 +4995,10 @@
   return false;
 }
 
-bool SelectionDAG::isKnownNeverZero(SDValue Op) const {
+bool SelectionDAG::isKnownNeverZero(SDValue Op, unsigned Depth) const {
+  if (Depth++ >= MaxRecursionDepth)
+    return false; // Limit search depth.
+
   assert(!Op.getValueType().isFloatingPoint() &&
          "Floating point types unsupported - use isKnownNeverZeroFloat");
 
@@ -5005,8 +5011,8 @@
   switch (Op.getOpcode()) {
   default: break;
   case ISD::OR:
-    if (isKnownNeverZero(Op.getOperand(1)) ||
-        isKnownNeverZero(Op.getOperand(0)))
+    if (isKnownNeverZero(Op.getOperand(1), Depth) ||
+        isKnownNeverZero(Op.getOperand(0), Depth))
       return true;
     break;
   }
Index: llvm/include/llvm/CodeGen/SelectionDAG.h
===================================================================
--- llvm/include/llvm/CodeGen/SelectionDAG.h
+++ llvm/include/llvm/CodeGen/SelectionDAG.h
@@ -1990,7 +1990,7 @@
   /// Test if the given value is known to have exactly one bit set. This differs
   /// from computeKnownBits in that it doesn't necessarily determine which bit
   /// is set.
-  bool isKnownToBeAPowerOfTwo(SDValue Val) const;
+  bool isKnownToBeAPowerOfTwo(SDValue Val, unsigned Depth = 0) const;
 
   /// Return the number of times the sign bit of the register is replicated into
   /// the other bits. We know that at least 1 bit is always equal to the sign
@@ -2098,7 +2098,7 @@
   bool isKnownNeverZeroFloat(SDValue Op) const;
 
   /// Test whether the given SDValue is known to contain non-zero value(s).
-  bool isKnownNeverZero(SDValue Op) const;
+  bool isKnownNeverZero(SDValue Op, unsigned Depth = 0) const;
 
   /// Test whether two SDValues are known to compare equal. This
   /// is true if they are the same value, or if one is negative zero and the


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