Fix ctlz and cttz. llvm definition requires them to return number of bits in of the src type when value is zero.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@45029 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 1d64b1d..c2f2736 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -5352,15 +5352,26 @@
Op = Op.getOperand(0);
if (VT == MVT::i8) {
+ // Zero extend to i32 since there is not an i8 bsr.
OpVT = MVT::i32;
Op = DAG.getNode(ISD::ZERO_EXTEND, OpVT, Op);
}
- if (VT == MVT::i32 || VT == MVT::i64)
- return DAG.getNode(ISD::XOR, OpVT, DAG.getNode(X86ISD::BSR, OpVT, Op),
- DAG.getConstant(NumBits-1, OpVT));
- Op = DAG.getNode(ISD::SUB, OpVT, DAG.getConstant(NumBits-1, OpVT),
- DAG.getNode(X86ISD::BSR, OpVT, Op));
+ // Issue a bsr (scan bits in reverse) which also sets EFLAGS.
+ SDVTList VTs = DAG.getVTList(OpVT, MVT::i32);
+ Op = DAG.getNode(X86ISD::BSR, VTs, Op);
+
+ // If src is zero (i.e. bsr sets ZF), returns NumBits.
+ SmallVector<SDOperand, 4> Ops;
+ Ops.push_back(Op);
+ Ops.push_back(DAG.getConstant(NumBits+NumBits-1, OpVT));
+ Ops.push_back(DAG.getConstant(X86::COND_E, MVT::i8));
+ Ops.push_back(Op.getValue(1));
+ Op = DAG.getNode(X86ISD::CMOV, OpVT, &Ops[0], 4);
+
+ // Finally xor with NumBits-1.
+ Op = DAG.getNode(ISD::XOR, OpVT, Op, DAG.getConstant(NumBits-1, OpVT));
+
if (VT == MVT::i8)
Op = DAG.getNode(ISD::TRUNCATE, MVT::i8, Op);
return Op;
@@ -5369,13 +5380,26 @@
SDOperand X86TargetLowering::LowerCTTZ(SDOperand Op, SelectionDAG &DAG) {
MVT::ValueType VT = Op.getValueType();
MVT::ValueType OpVT = VT;
+ unsigned NumBits = MVT::getSizeInBits(VT);
Op = Op.getOperand(0);
if (VT == MVT::i8) {
OpVT = MVT::i32;
Op = DAG.getNode(ISD::ZERO_EXTEND, OpVT, Op);
}
- Op = DAG.getNode(X86ISD::BSF, OpVT, Op);
+
+ // Issue a bsf (scan bits forward) which also sets EFLAGS.
+ SDVTList VTs = DAG.getVTList(OpVT, MVT::i32);
+ Op = DAG.getNode(X86ISD::BSF, VTs, Op);
+
+ // If src is zero (i.e. bsf sets ZF), returns NumBits.
+ SmallVector<SDOperand, 4> Ops;
+ Ops.push_back(Op);
+ Ops.push_back(DAG.getConstant(NumBits, OpVT));
+ Ops.push_back(DAG.getConstant(X86::COND_E, MVT::i8));
+ Ops.push_back(Op.getValue(1));
+ Op = DAG.getNode(X86ISD::CMOV, OpVT, &Ops[0], 4);
+
if (VT == MVT::i8)
Op = DAG.getNode(ISD::TRUNCATE, MVT::i8, Op);
return Op;