[AArch64] Lower sdiv x, pow2 using add + select + shift.
The target-independent DAGcombiner will generate:
asr w1, X, #31 w1 = splat sign bit.
add X, X, w1, lsr #28 X = X + 0 or pow2-1
asr w0, X, asr #4 w0 = X/pow2
However, the add + shifts is expensive, so generate:
add w0, X, 15 w0 = X + pow2-1
cmp X, wzr X - 0
csel X, w0, X, lt X = (X < 0) ? X + pow2-1 : X;
asr w0, X, asr 4 w0 = X/pow2
llvm-svn: 213758
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 35d6256..3a292c5 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -304,6 +304,7 @@
SDValue CombineConsecutiveLoads(SDNode *N, EVT VT);
SDValue ConstantFoldBITCASTofBUILD_VECTOR(SDNode *, EVT);
SDValue BuildSDIV(SDNode *N);
+ SDValue BuildSDIVPow2(SDNode *N);
SDValue BuildUDIV(SDNode *N);
SDValue MatchBSwapHWordLow(SDNode *N, SDValue N0, SDValue N1,
bool DemandHighBits = true);
@@ -2033,6 +2034,11 @@
if (TLI.isPow2DivCheap())
return SDValue();
+ // Target-specific implementation of sdiv x, pow2.
+ SDValue Res = BuildSDIVPow2(N);
+ if (Res.getNode())
+ return Res;
+
unsigned lg2 = N1C->getAPIntValue().countTrailingZeros();
// Splat the sign bit into the register
@@ -11482,9 +11488,9 @@
return TLI.SimplifySetCC(VT, N0, N1, Cond, foldBooleans, DagCombineInfo, DL);
}
-/// BuildSDIVSequence - Given an ISD::SDIV node expressing a divide by constant,
-/// return a DAG expression to select that will generate the same value by
-/// multiplying by a magic number. See:
+/// BuildSDIV - Given an ISD::SDIV node expressing a divide by constant, return
+/// a DAG expression to select that will generate the same value by multiplying
+/// by a magic number. See:
/// <http://the.wall.riscom.net/books/proc/ppc/cwg/code2.html>
SDValue DAGCombiner::BuildSDIV(SDNode *N) {
ConstantSDNode *C = isConstOrConstSplat(N->getOperand(1));
@@ -11504,6 +11510,26 @@
return S;
}
+/// BuildSDIVPow2 - Given an ISD::SDIV node expressing a divide by constant
+/// power of 2, return a DAG expression to select that will generate the same
+/// value by right shifting.
+SDValue DAGCombiner::BuildSDIVPow2(SDNode *N) {
+ ConstantSDNode *C = isConstOrConstSplat(N->getOperand(1));
+ if (!C)
+ return SDValue();
+
+ // Avoid division by zero.
+ if (!C->getAPIntValue())
+ return SDValue();
+
+ std::vector<SDNode *> Built;
+ SDValue S = TLI.BuildSDIVPow2(N, C->getAPIntValue(), DAG, &Built);
+
+ for (SDNode *N : Built)
+ AddToWorklist(N);
+ return S;
+}
+
/// BuildUDIV - Given an ISD::UDIV node expressing a divide by constant,
/// return a DAG expression to select that will generate the same value by
/// multiplying by a magic number. See: