Add a DAGCombine to turn (ctpop x) u< 2 into (x & x-1) == 0.
This shaves off 4 popcounts from the hacked 186.crafty source.
This is enabled even when a native popcount instruction is available. The
combined code is one operation longer but it should be faster nevertheless.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123621 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index f9e0992..1621d61 100644
--- a/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -1870,6 +1870,30 @@
}
}
+ SDValue CTPOP = N0;
+ // Look through truncs that don't change the value of a ctpop.
+ if (N0.hasOneUse() && N0.getOpcode() == ISD::TRUNCATE)
+ CTPOP = N0.getOperand(0);
+
+ if (CTPOP.hasOneUse() && CTPOP.getOpcode() == ISD::CTPOP &&
+ (N0 == CTPOP || N0.getValueType().getSizeInBits() >=
+ Log2_32_Ceil(CTPOP.getValueType().getSizeInBits()))) {
+ EVT CTVT = CTPOP.getValueType();
+ SDValue CTOp = CTPOP.getOperand(0);
+
+ // (ctpop x) u< 2 -> (x & x-1) == 0
+ // (ctpop x) u> 1 -> (x & x-1) != 0
+ if ((Cond == ISD::SETULT && C1 == 2) || (Cond == ISD::SETUGT && C1 == 1)){
+ SDValue Sub = DAG.getNode(ISD::SUB, dl, CTVT, CTOp,
+ DAG.getConstant(1, CTVT));
+ SDValue And = DAG.getNode(ISD::AND, dl, CTVT, CTOp, Sub);
+ ISD::CondCode CC = Cond == ISD::SETULT ? ISD::SETEQ : ISD::SETNE;
+ return DAG.getSetCC(dl, VT, And, DAG.getConstant(0, CTVT), CC);
+ }
+
+ // TODO: (ctpop x) == 1 -> x && (x & x-1) == 0 iff ctpop is illegal.
+ }
+
// If the LHS is '(and load, const)', the RHS is 0,
// the test is for equality or unsigned, and all 1 bits of the const are
// in the same partial word, see if we can shorten the load.