Fix PR 8916 (qv for analysis), at least the immediate problem.

There's an inherent tension in DAGCombine between assuming
that things will be put in canonical form, and the Depth
mechanism that disables transformations when recursion gets
too deep.  It would not surprise me if there's a lot of little
bugs like this one waiting to be discovered.  The mechanism
seems fragile and I'd suggest looking at it from a design viewpoint.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123191 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 2 insertions, 1 deletions

diff --git a/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 396ebc15c6..f9e0992ea1 100644
--- a/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -1176,8 +1176,9 @@ bool TargetLowering::SimplifyDemandedBits(SDValue Op,
     // the RHS.
     if (ConstantSDNode *RHSC = dyn_cast<ConstantSDNode>(Op.getOperand(1))) {
       APInt LHSZero, LHSOne;
+      // Do not increment Depth here; that can cause an infinite loop.
       TLO.DAG.ComputeMaskedBits(Op.getOperand(0), NewMask,
-                                LHSZero, LHSOne, Depth+1);
+                                LHSZero, LHSOne, Depth);
       // If the LHS already has zeros where RHSC does, this and is dead.
       if ((LHSZero & NewMask) == (~RHSC->getAPIntValue() & NewMask))
         return TLO.CombineTo(Op, Op.getOperand(0));