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[DAGCombine][PowerPC] Simplify nabs by using legal smin operation
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Convert `0 - abs(x)` to `smin (x, -x)` if `smin` is a legal operation.

Verification: https://alive2.llvm.org/ce/z/vpquFR

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D92637
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@bzEq
bzEq committed Dec 8, 2020
1 parent 49599cb commit 44bd8ea
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Showing 4 changed files with 47 additions and 41 deletions.
4 changes: 3 additions & 1 deletion llvm/include/llvm/CodeGen/TargetLowering.h
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Expand Up @@ -4393,8 +4393,10 @@ class TargetLowering : public TargetLoweringBase {
/// (ABS x) -> (XOR (ADD x, (SRA x, type_size)), (SRA x, type_size))
/// \param N Node to expand
/// \param Result output after conversion
/// \param IsNegative indicate negated abs
/// \returns True, if the expansion was successful, false otherwise
bool expandABS(SDNode *N, SDValue &Result, SelectionDAG &DAG) const;
bool expandABS(SDNode *N, SDValue &Result, SelectionDAG &DAG,
bool IsNegative = false) const;

/// Turn load of vector type into a load of the individual elements.
/// \param LD load to expand
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16 changes: 5 additions & 11 deletions llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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Expand Up @@ -3193,18 +3193,12 @@ SDValue DAGCombiner::visitSUB(SDNode *N) {
return N1;
}

// Convert 0 - abs(x) -> Y = sra (X, size(X)-1); sub (Y, xor (X, Y)).
// Convert 0 - abs(x).
SDValue Result;
if (N1->getOpcode() == ISD::ABS &&
!TLI.isOperationLegalOrCustom(ISD::ABS, VT)) {
SDValue X = N1->getOperand(0);
SDValue Shift =
DAG.getNode(ISD::SRA, DL, VT, X,
DAG.getConstant(BitWidth - 1, DL, getShiftAmountTy(VT)));
SDValue Xor = DAG.getNode(ISD::XOR, DL, VT, X, Shift);
AddToWorklist(Shift.getNode());
AddToWorklist(Xor.getNode());
return DAG.getNode(ISD::SUB, DL, VT, Shift, Xor);
}
!TLI.isOperationLegalOrCustom(ISD::ABS, VT) &&
TLI.expandABS(N1.getNode(), Result, DAG, true))
return Result;
}

// Canonicalize (sub -1, x) -> ~x, i.e. (xor x, -1)
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35 changes: 27 additions & 8 deletions llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
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Expand Up @@ -6816,39 +6816,58 @@ bool TargetLowering::expandCTTZ(SDNode *Node, SDValue &Result,
}

bool TargetLowering::expandABS(SDNode *N, SDValue &Result,
SelectionDAG &DAG) const {
SelectionDAG &DAG, bool IsNegative) const {
SDLoc dl(N);
EVT VT = N->getValueType(0);
EVT ShVT = getShiftAmountTy(VT, DAG.getDataLayout());
SDValue Op = N->getOperand(0);

// abs(x) -> smax(x,sub(0,x))
if (isOperationLegal(ISD::SUB, VT) && isOperationLegal(ISD::SMAX, VT)) {
if (!IsNegative && isOperationLegal(ISD::SUB, VT) &&
isOperationLegal(ISD::SMAX, VT)) {
SDValue Zero = DAG.getConstant(0, dl, VT);
Result = DAG.getNode(ISD::SMAX, dl, VT, Op,
DAG.getNode(ISD::SUB, dl, VT, Zero, Op));
return true;
}

// abs(x) -> umin(x,sub(0,x))
if (isOperationLegal(ISD::SUB, VT) && isOperationLegal(ISD::UMIN, VT)) {
if (!IsNegative && isOperationLegal(ISD::SUB, VT) &&
isOperationLegal(ISD::UMIN, VT)) {
SDValue Zero = DAG.getConstant(0, dl, VT);
Result = DAG.getNode(ISD::UMIN, dl, VT, Op,
DAG.getNode(ISD::SUB, dl, VT, Zero, Op));
return true;
}

// 0 - abs(x) -> smin(x, sub(0,x))
if (IsNegative && isOperationLegal(ISD::SUB, VT) &&
isOperationLegal(ISD::SMIN, VT)) {
SDValue Zero = DAG.getConstant(0, dl, VT);
Result = DAG.getNode(ISD::SMIN, dl, VT, Op,
DAG.getNode(ISD::SUB, dl, VT, Zero, Op));
return true;
}

// Only expand vector types if we have the appropriate vector operations.
if (VT.isVector() && (!isOperationLegalOrCustom(ISD::SRA, VT) ||
!isOperationLegalOrCustom(ISD::ADD, VT) ||
!isOperationLegalOrCustomOrPromote(ISD::XOR, VT)))
if (VT.isVector() &&
(!isOperationLegalOrCustom(ISD::SRA, VT) ||
(!IsNegative && !isOperationLegalOrCustom(ISD::ADD, VT)) ||
(IsNegative && !isOperationLegalOrCustom(ISD::SUB, VT)) ||
!isOperationLegalOrCustomOrPromote(ISD::XOR, VT)))
return false;

SDValue Shift =
DAG.getNode(ISD::SRA, dl, VT, Op,
DAG.getConstant(VT.getScalarSizeInBits() - 1, dl, ShVT));
SDValue Add = DAG.getNode(ISD::ADD, dl, VT, Op, Shift);
Result = DAG.getNode(ISD::XOR, dl, VT, Add, Shift);
if (!IsNegative) {
SDValue Add = DAG.getNode(ISD::ADD, dl, VT, Op, Shift);
Result = DAG.getNode(ISD::XOR, dl, VT, Add, Shift);
} else {
// 0 - abs(x) -> Y = sra (X, size(X)-1); sub (Y, xor (X, Y))
SDValue Xor = DAG.getNode(ISD::XOR, dl, VT, Op, Shift);
Result = DAG.getNode(ISD::SUB, dl, VT, Shift, Xor);
}
return true;
}

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33 changes: 12 additions & 21 deletions llvm/test/CodeGen/PowerPC/neg-abs.ll
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Expand Up @@ -24,13 +24,9 @@ define i64@neg_abs(i64 %x) {
define <2 x i64> @neg_abs_v2i64(<2 x i64> %0) {
; CHECK-LE-LABEL: neg_abs_v2i64:
; CHECK-LE: # %bb.0:
; CHECK-LE-NEXT: addis r3, r2, .LCPI1_0@toc@ha
; CHECK-LE-NEXT: addi r3, r3, .LCPI1_0@toc@l
; CHECK-LE-NEXT: lxvd2x vs0, 0, r3
; CHECK-LE-NEXT: xxswapd vs35, vs0
; CHECK-LE-NEXT: vsrad v3, v2, v3
; CHECK-LE-NEXT: xxlxor vs34, vs34, vs35
; CHECK-LE-NEXT: vsubudm v2, v3, v2
; CHECK-LE-NEXT: xxlxor vs35, vs35, vs35
; CHECK-LE-NEXT: vsubudm v3, v3, v2
; CHECK-LE-NEXT: vminsd v2, v2, v3
; CHECK-LE-NEXT: blr
%abs = call <2 x i64> @llvm.abs.v2i64(<2 x i64> %0, i1 true)
%neg.abs = sub <2 x i64> zeroinitializer, %abs
Expand All @@ -40,12 +36,9 @@ define <2 x i64> @neg_abs_v2i64(<2 x i64> %0) {
define <4 x i32> @neg_abs_v4i32(<4 x i32> %0) {
; CHECK-LE-LABEL: neg_abs_v4i32:
; CHECK-LE: # %bb.0:
; CHECK-LE-NEXT: vspltisw v3, -16
; CHECK-LE-NEXT: vspltisw v4, 15
; CHECK-LE-NEXT: vsubuwm v3, v4, v3
; CHECK-LE-NEXT: vsraw v3, v2, v3
; CHECK-LE-NEXT: xxlxor vs34, vs34, vs35
; CHECK-LE-NEXT: vsubuwm v2, v3, v2
; CHECK-LE-NEXT: xxlxor vs35, vs35, vs35
; CHECK-LE-NEXT: vsubuwm v3, v3, v2
; CHECK-LE-NEXT: vminsw v2, v2, v3
; CHECK-LE-NEXT: blr
%abs = call <4 x i32> @llvm.abs.v4i32(<4 x i32> %0, i1 true)
%neg.abs = sub <4 x i32> zeroinitializer, %abs
Expand All @@ -55,10 +48,9 @@ define <4 x i32> @neg_abs_v4i32(<4 x i32> %0) {
define <8 x i16> @neg_abs_v8i16(<8 x i16> %0) {
; CHECK-LE-LABEL: neg_abs_v8i16:
; CHECK-LE: # %bb.0:
; CHECK-LE-NEXT: vspltish v3, 15
; CHECK-LE-NEXT: vsrah v3, v2, v3
; CHECK-LE-NEXT: xxlxor vs34, vs34, vs35
; CHECK-LE-NEXT: vsubuhm v2, v3, v2
; CHECK-LE-NEXT: xxlxor vs35, vs35, vs35
; CHECK-LE-NEXT: vsubuhm v3, v3, v2
; CHECK-LE-NEXT: vminsh v2, v2, v3
; CHECK-LE-NEXT: blr
%abs = call <8 x i16> @llvm.abs.v8i16(<8 x i16> %0, i1 true)
%neg.abs = sub <8 x i16> zeroinitializer, %abs
Expand All @@ -68,10 +60,9 @@ define <8 x i16> @neg_abs_v8i16(<8 x i16> %0) {
define <16 x i8> @neg_abs_v16i8(<16 x i8> %0) {
; CHECK-LE-LABEL: neg_abs_v16i8:
; CHECK-LE: # %bb.0:
; CHECK-LE-NEXT: vspltisb v3, 7
; CHECK-LE-NEXT: vsrab v3, v2, v3
; CHECK-LE-NEXT: xxlxor vs34, vs34, vs35
; CHECK-LE-NEXT: vsububm v2, v3, v2
; CHECK-LE-NEXT: xxlxor vs35, vs35, vs35
; CHECK-LE-NEXT: vsububm v3, v3, v2
; CHECK-LE-NEXT: vminsb v2, v2, v3
; CHECK-LE-NEXT: blr
%abs = call <16 x i8> @llvm.abs.v16i8(<16 x i8> %0, i1 true)
%neg.abs = sub <16 x i8> zeroinitializer, %abs
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