[DAG] Don't pull the binary operation though the shift if the operands have opaque constants.
During DAGCombine visitShiftByConstant assumes that certain binary operations
with only constant operands can always be folded successfully. This is no longer
true when the constant is opaque. This commit fixes visitShiftByConstant by not
performing the optimization for opaque constants. Otherwise we would end up in
an infinite DAGCombine loop.
llvm-svn: 200900
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 32c07ad..9b84e4d 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -3732,6 +3732,12 @@
/// visitShiftByConstant - Handle transforms common to the three shifts, when
/// the shift amount is a constant.
SDValue DAGCombiner::visitShiftByConstant(SDNode *N, unsigned Amt) {
+ assert(isa<ConstantSDNode>(N->getOperand(1)) &&
+ "Expected an ConstantSDNode operand.");
+ // We can't and shouldn't fold opaque constants.
+ if (cast<ConstantSDNode>(N->getOperand(1))->isOpaque())
+ return SDValue();
+
SDNode *LHS = N->getOperand(0).getNode();
if (!LHS->hasOneUse()) return SDValue();
@@ -3757,9 +3763,9 @@
break;
}
- // We require the RHS of the binop to be a constant as well.
+ // We require the RHS of the binop to be a constant and not opaque as well.
ConstantSDNode *BinOpCst = dyn_cast<ConstantSDNode>(LHS->getOperand(1));
- if (!BinOpCst) return SDValue();
+ if (!BinOpCst || BinOpCst->isOpaque()) return SDValue();
// FIXME: disable this unless the input to the binop is a shift by a constant.
// If it is not a shift, it pessimizes some common cases like:
@@ -3789,6 +3795,7 @@
SDValue NewRHS = DAG.getNode(N->getOpcode(), SDLoc(LHS->getOperand(1)),
N->getValueType(0),
LHS->getOperand(1), N->getOperand(1));
+ assert(isa<ConstantSDNode>(NewRHS) && "Folding was not successful!");
// Create the new shift.
SDValue NewShift = DAG.getNode(N->getOpcode(),