third time around: instead of disabling this completely,
only disable it if we don't know it will be obviously profitable.
Still fixme, but less so. :)
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@44658 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index ba3c0ac..fd0df3a 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -2134,12 +2134,6 @@
/// visitShiftByConstant - Handle transforms common to the three shifts, when
/// the shift amount is a constant.
SDOperand DAGCombiner::visitShiftByConstant(SDNode *N, unsigned Amt) {
- // FIXME: disable this for now. This pessimizes some common cases like:
- //
- //void foo(int *X, int i) { X[i & 1235] = 1; }
- //int bar(int *X, int i) { return X[i & 255]; }
- return SDOperand();
-
SDNode *LHS = N->getOperand(0).Val;
if (!LHS->hasOneUse()) return SDOperand();
@@ -2169,6 +2163,19 @@
ConstantSDNode *BinOpCst = dyn_cast<ConstantSDNode>(LHS->getOperand(1));
if (!BinOpCst) return SDOperand();
+
+ // FIXME: disable this for unless the input to the binop is a shift by a
+ // constant. If it is not a shift, it pessimizes some common cases like:
+ //
+ //void foo(int *X, int i) { X[i & 1235] = 1; }
+ //int bar(int *X, int i) { return X[i & 255]; }
+ SDNode *BinOpLHSVal = LHS->getOperand(0).Val;
+ if ((BinOpLHSVal->getOpcode() != ISD::SHL &&
+ BinOpLHSVal->getOpcode() != ISD::SRA &&
+ BinOpLHSVal->getOpcode() != ISD::SRL) ||
+ !isa<ConstantSDNode>(BinOpLHSVal->getOperand(1)))
+ return SDOperand();
+
MVT::ValueType VT = N->getValueType(0);
// If this is a signed shift right, and the high bit is modified