[SelectionDAG] Don't subject ConstantSDNodes to the depth limit in computeKnownBits and ComputeNumSignBits.

We don't need to do any additional recursion, we just need to analyze the APInt stored in the node. This matches what the ValueTracking versions do for IR.

llvm-svn: 316256

1 files changed, 13 insertions, 10 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 4b0a5e07238..dfb097ac770 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2089,6 +2089,14 @@ void SelectionDAG::computeKnownBits(SDValue Op, KnownBits &Known,
   unsigned BitWidth = Op.getScalarValueSizeInBits();
 
   Known = KnownBits(BitWidth);   // Don't know anything.
+
+  if (auto *C = dyn_cast<ConstantSDNode>(Op)) {
+    // We know all of the bits for a constant!
+    Known.One = C->getAPIntValue();
+    Known.Zero = ~Known.One;
+    return;
+  }
+
   if (Depth == 6)
     return;  // Limit search depth.
 
@@ -2100,11 +2108,6 @@ void SelectionDAG::computeKnownBits(SDValue Op, KnownBits &Known,
 
   unsigned Opcode = Op.getOpcode();
   switch (Opcode) {
-  case ISD::Constant:
-    // We know all of the bits for a constant!
-    Known.One = cast<ConstantSDNode>(Op)->getAPIntValue();
-    Known.Zero = ~Known.One;
-    break;
   case ISD::BUILD_VECTOR:
     // Collect the known bits that are shared by every demanded vector element.
     assert(NumElts == Op.getValueType().getVectorNumElements() &&
@@ -2963,6 +2966,11 @@ unsigned SelectionDAG::ComputeNumSignBits(SDValue Op, const APInt &DemandedElts,
   unsigned Tmp, Tmp2;
   unsigned FirstAnswer = 1;
 
+  if (auto *C = dyn_cast<ConstantSDNode>(Op)) {
+    const APInt &Val = cast<ConstantSDNode>(Op)->getAPIntValue();
+    return Val.getNumSignBits();
+  }
+
   if (Depth == 6)
     return 1;  // Limit search depth.
 
@@ -2978,11 +2986,6 @@ unsigned SelectionDAG::ComputeNumSignBits(SDValue Op, const APInt &DemandedElts,
     Tmp = cast<VTSDNode>(Op.getOperand(1))->getVT().getSizeInBits();
     return VTBits-Tmp;
 
-  case ISD::Constant: {
-    const APInt &Val = cast<ConstantSDNode>(Op)->getAPIntValue();
-    return Val.getNumSignBits();
-  }
-
   case ISD::BUILD_VECTOR:
     Tmp = VTBits;
     for (unsigned i = 0, e = Op.getNumOperands(); (i < e) && (Tmp > 1); ++i) {