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[DAG] Replace DAGCombiner::ConstantFoldBITCASTofBUILD_VECTOR with SelectionDAG::FoldConstantBuildVector #147037

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Merged
merged 4 commits into from
Jul 7, 2025
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Merged

[DAG] Replace DAGCombiner::ConstantFoldBITCASTofBUILD_VECTOR with SelectionDAG::FoldConstantBuildVector #147037

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14bfeb6
[DAG] Replace DAGCombiner::ConstantFoldBITCASTofBUILD_VECTOR with Sel…
RKSimon Jul 4, 2025
33fa1f9
Merge branch 'main' into dag-fold-constant-buildvector
RKSimon Jul 4, 2025
771974e
Merge branch 'main' into dag-fold-constant-buildvector
RKSimon Jul 7, 2025
51eef87
Add missing early-out
RKSimon Jul 7, 2025
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5 changes: 5 additions & 0 deletions llvm/include/llvm/CodeGen/SelectionDAG.h
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Original file line number Diff line number Diff line change
Expand Up @@ -2030,6 +2030,11 @@ class SelectionDAG {
LLVM_ABI SDValue foldConstantFPMath(unsigned Opcode, const SDLoc &DL, EVT VT,
ArrayRef<SDValue> Ops);

/// Fold BUILD_VECTOR of constants/undefs to the destination type
/// BUILD_VECTOR of constants/undefs elements.
LLVM_ABI SDValue FoldConstantBuildVector(BuildVectorSDNode *BV,
const SDLoc &DL, EVT DstEltVT);

/// Constant fold a setcc to true or false.
LLVM_ABI SDValue FoldSetCC(EVT VT, SDValue N1, SDValue N2, ISD::CondCode Cond,
const SDLoc &dl);
Expand Down
82 changes: 2 additions & 80 deletions llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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Expand Up @@ -638,7 +638,6 @@ namespace {
SDValue mergeInsertEltWithShuffle(SDNode *N, unsigned InsIndex);
SDValue combineInsertEltToShuffle(SDNode *N, unsigned InsIndex);
SDValue combineInsertEltToLoad(SDNode *N, unsigned InsIndex);
SDValue ConstantFoldBITCASTofBUILD_VECTOR(SDNode *, EVT);
SDValue BuildSDIV(SDNode *N);
SDValue BuildSDIVPow2(SDNode *N);
SDValue BuildUDIV(SDNode *N);
Expand Down Expand Up @@ -16431,8 +16430,8 @@ SDValue DAGCombiner::visitBITCAST(SDNode *N) {
TLI.isTypeLegal(VT.getVectorElementType()))) &&
N0.getOpcode() == ISD::BUILD_VECTOR && N0->hasOneUse() &&
cast<BuildVectorSDNode>(N0)->isConstant())
return ConstantFoldBITCASTofBUILD_VECTOR(N0.getNode(),
VT.getVectorElementType());
return DAG.FoldConstantBuildVector(cast<BuildVectorSDNode>(N0), SDLoc(N),
VT.getVectorElementType());

// If the input is a constant, let getNode fold it.
if (isIntOrFPConstant(N0)) {
Expand Down Expand Up @@ -16825,83 +16824,6 @@ SDValue DAGCombiner::visitFREEZE(SDNode *N) {
return DAG.getNode(N0.getOpcode(), DL, N0->getVTList(), Ops, SafeFlags);
}

/// We know that BV is a build_vector node with Constant, ConstantFP or Undef
/// operands. DstEltVT indicates the destination element value type.
SDValue DAGCombiner::
ConstantFoldBITCASTofBUILD_VECTOR(SDNode *BV, EVT DstEltVT) {
EVT SrcEltVT = BV->getValueType(0).getVectorElementType();

// If this is already the right type, we're done.
if (SrcEltVT == DstEltVT) return SDValue(BV, 0);

unsigned SrcBitSize = SrcEltVT.getSizeInBits();
unsigned DstBitSize = DstEltVT.getSizeInBits();

// If this is a conversion of N elements of one type to N elements of another
// type, convert each element. This handles FP<->INT cases.
if (SrcBitSize == DstBitSize) {
SmallVector<SDValue, 8> Ops;
for (SDValue Op : BV->op_values()) {
// If the vector element type is not legal, the BUILD_VECTOR operands
// are promoted and implicitly truncated. Make that explicit here.
if (Op.getValueType() != SrcEltVT)
Op = DAG.getNode(ISD::TRUNCATE, SDLoc(BV), SrcEltVT, Op);
Ops.push_back(DAG.getBitcast(DstEltVT, Op));
AddToWorklist(Ops.back().getNode());
}
EVT VT = EVT::getVectorVT(*DAG.getContext(), DstEltVT,
BV->getValueType(0).getVectorNumElements());
return DAG.getBuildVector(VT, SDLoc(BV), Ops);
}

// Otherwise, we're growing or shrinking the elements. To avoid having to
// handle annoying details of growing/shrinking FP values, we convert them to
// int first.
if (SrcEltVT.isFloatingPoint()) {
// Convert the input float vector to a int vector where the elements are the
// same sizes.
EVT IntVT = EVT::getIntegerVT(*DAG.getContext(), SrcEltVT.getSizeInBits());
BV = ConstantFoldBITCASTofBUILD_VECTOR(BV, IntVT).getNode();
SrcEltVT = IntVT;
}

// Now we know the input is an integer vector. If the output is a FP type,
// convert to integer first, then to FP of the right size.
if (DstEltVT.isFloatingPoint()) {
EVT TmpVT = EVT::getIntegerVT(*DAG.getContext(), DstEltVT.getSizeInBits());
SDNode *Tmp = ConstantFoldBITCASTofBUILD_VECTOR(BV, TmpVT).getNode();

// Next, convert to FP elements of the same size.
return ConstantFoldBITCASTofBUILD_VECTOR(Tmp, DstEltVT);
}

// Okay, we know the src/dst types are both integers of differing types.
assert(SrcEltVT.isInteger() && DstEltVT.isInteger());

// TODO: Should ConstantFoldBITCASTofBUILD_VECTOR always take a
// BuildVectorSDNode?
auto *BVN = cast<BuildVectorSDNode>(BV);

// Extract the constant raw bit data.
BitVector UndefElements;
SmallVector<APInt> RawBits;
bool IsLE = DAG.getDataLayout().isLittleEndian();
if (!BVN->getConstantRawBits(IsLE, DstBitSize, RawBits, UndefElements))
return SDValue();

SDLoc DL(BV);
SmallVector<SDValue, 8> Ops;
for (unsigned I = 0, E = RawBits.size(); I != E; ++I) {
if (UndefElements[I])
Ops.push_back(DAG.getUNDEF(DstEltVT));
else
Ops.push_back(DAG.getConstant(RawBits[I], DL, DstEltVT));
}

EVT VT = EVT::getVectorVT(*DAG.getContext(), DstEltVT, Ops.size());
return DAG.getBuildVector(VT, DL, Ops);
}

// Returns true if floating point contraction is allowed on the FMUL-SDValue
// `N`
static bool isContractableFMUL(const TargetOptions &Options, SDValue N) {
Expand Down
72 changes: 72 additions & 0 deletions llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -7280,6 +7280,78 @@ SDValue SelectionDAG::foldConstantFPMath(unsigned Opcode, const SDLoc &DL,
return SDValue();
}

SDValue SelectionDAG::FoldConstantBuildVector(BuildVectorSDNode *BV,
const SDLoc &DL, EVT DstEltVT) {
EVT SrcEltVT = BV->getValueType(0).getVectorElementType();

// If this is already the right type, we're done.
if (SrcEltVT == DstEltVT)
return SDValue(BV, 0);

unsigned SrcBitSize = SrcEltVT.getSizeInBits();
unsigned DstBitSize = DstEltVT.getSizeInBits();

// If this is a conversion of N elements of one type to N elements of another
// type, convert each element. This handles FP<->INT cases.
if (SrcBitSize == DstBitSize) {
SmallVector<SDValue, 8> Ops;
for (SDValue Op : BV->op_values()) {
// If the vector element type is not legal, the BUILD_VECTOR operands
// are promoted and implicitly truncated. Make that explicit here.
if (Op.getValueType() != SrcEltVT)
Op = getNode(ISD::TRUNCATE, DL, SrcEltVT, Op);
Ops.push_back(getBitcast(DstEltVT, Op));
}
EVT VT = EVT::getVectorVT(*getContext(), DstEltVT,
BV->getValueType(0).getVectorNumElements());
return getBuildVector(VT, DL, Ops);
}

// Otherwise, we're growing or shrinking the elements. To avoid having to
// handle annoying details of growing/shrinking FP values, we convert them to
// int first.
if (SrcEltVT.isFloatingPoint()) {
// Convert the input float vector to a int vector where the elements are the
// same sizes.
EVT IntEltVT = EVT::getIntegerVT(*getContext(), SrcEltVT.getSizeInBits());
if (SDValue Tmp = FoldConstantBuildVector(BV, DL, IntEltVT))
return FoldConstantBuildVector(cast<BuildVectorSDNode>(Tmp), DL,
DstEltVT);
return SDValue();
}

// Now we know the input is an integer vector. If the output is a FP type,
// convert to integer first, then to FP of the right size.
if (DstEltVT.isFloatingPoint()) {
EVT IntEltVT = EVT::getIntegerVT(*getContext(), DstEltVT.getSizeInBits());
if (SDValue Tmp = FoldConstantBuildVector(BV, DL, IntEltVT))
return FoldConstantBuildVector(cast<BuildVectorSDNode>(Tmp), DL,
DstEltVT);
return SDValue();
}

// Okay, we know the src/dst types are both integers of differing types.
assert(SrcEltVT.isInteger() && DstEltVT.isInteger());

// Extract the constant raw bit data.
BitVector UndefElements;
SmallVector<APInt> RawBits;
bool IsLE = getDataLayout().isLittleEndian();
if (!BV->getConstantRawBits(IsLE, DstBitSize, RawBits, UndefElements))
return SDValue();

SmallVector<SDValue, 8> Ops;
for (unsigned I = 0, E = RawBits.size(); I != E; ++I) {
if (UndefElements[I])
Ops.push_back(getUNDEF(DstEltVT));
else
Ops.push_back(getConstant(RawBits[I], DL, DstEltVT));
}

EVT VT = EVT::getVectorVT(*getContext(), DstEltVT, Ops.size());
return getBuildVector(VT, DL, Ops);
}

SDValue SelectionDAG::getAssertAlign(const SDLoc &DL, SDValue Val, Align A) {
assert(Val.getValueType().isInteger() && "Invalid AssertAlign!");

Expand Down
10 changes: 5 additions & 5 deletions llvm/test/CodeGen/AMDGPU/llvm.amdgcn.iglp.AFLCustomIRMutator.opt.ll
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Expand Up @@ -5,18 +5,19 @@ define amdgpu_kernel void @test_iglp_opt_rev_mfma_gemm(<1 x i64> %L1) {
; GCN-LABEL: test_iglp_opt_rev_mfma_gemm:
; GCN: ; %bb.0: ; %entry
; GCN-NEXT: v_mov_b32_e32 v32, 0
; GCN-NEXT: ds_read_b128 v[0:3], v32
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Why are there any test changes?

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I converted the code to be recursive to make error handling easier and it now shares a common SDLoc

; GCN-NEXT: s_load_dwordx2 s[0:1], s[8:9], 0x0
; GCN-NEXT: ds_read_b128 v[28:31], v32 offset:112
; GCN-NEXT: ds_read_b128 v[24:27], v32 offset:96
; GCN-NEXT: ds_read_b128 v[20:23], v32 offset:80
; GCN-NEXT: ds_read_b128 v[16:19], v32 offset:64
; GCN-NEXT: ds_read_b128 v[0:3], v32
; GCN-NEXT: ds_read_b128 v[4:7], v32 offset:16
; GCN-NEXT: ds_read_b128 v[8:11], v32 offset:32
; GCN-NEXT: ds_read_b128 v[12:15], v32 offset:48
; GCN-NEXT: v_mov_b32_e32 v34, 0
; GCN-NEXT: v_mov_b32_e32 v35, v34
; GCN-NEXT: s_waitcnt lgkmcnt(0)
; GCN-NEXT: ds_write_b128 v32, v[0:3]
; GCN-NEXT: v_mov_b32_e32 v0, 0
; GCN-NEXT: v_mov_b32_e32 v1, v0
; GCN-NEXT: s_cmp_lg_u64 s[0:1], 0
; GCN-NEXT: ; iglp_opt mask(0x00000001)
; GCN-NEXT: ds_write_b128 v32, v[28:31] offset:112
Expand All @@ -26,8 +27,7 @@ define amdgpu_kernel void @test_iglp_opt_rev_mfma_gemm(<1 x i64> %L1) {
; GCN-NEXT: ds_write_b128 v32, v[12:15] offset:48
; GCN-NEXT: ds_write_b128 v32, v[8:11] offset:32
; GCN-NEXT: ds_write_b128 v32, v[4:7] offset:16
; GCN-NEXT: ds_write_b128 v32, v[0:3]
; GCN-NEXT: ds_write_b64 v32, v[34:35]
; GCN-NEXT: ds_write_b64 v32, v[0:1]
; GCN-NEXT: s_endpgm
entry:
call void @llvm.amdgcn.iglp.opt(i32 1)
Expand Down