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DAG: Fold bitcast of scalar_to_vector to anyext #122660

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Merged
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Jan 13, 2025
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DAG: Fold bitcast of scalar_to_vector to anyext #122660

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068a622
AMDGPU: Add baseline test for bitcast of scalar_to_vector combine
arsenm Jan 13, 2025
78675d1
DAG: Fold bitcast of scalar_to_vector to anyext
arsenm Jan 13, 2025
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8 changes: 8 additions & 0 deletions llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -16012,6 +16012,14 @@ SDValue DAGCombiner::visitBITCAST(SDNode *N) {
if (SDValue CombineLD = CombineConsecutiveLoads(N0.getNode(), VT))
return CombineLD;

// int_vt (bitcast (vec_vt (scalar_to_vector elt_vt:x)))
// => int_vt (any_extend elt_vt:x)
if (N0.getOpcode() == ISD::SCALAR_TO_VECTOR && VT.isScalarInteger()) {
SDValue SrcScalar = N0.getOperand(0);
if (SrcScalar.getValueType().isScalarInteger())
return DAG.getNode(ISD::ANY_EXTEND, SDLoc(N), VT, SrcScalar);
}

// Remove double bitcasts from shuffles - this is often a legacy of
// XformToShuffleWithZero being used to combine bitmaskings (of
// float vectors bitcast to integer vectors) into shuffles.
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30 changes: 30 additions & 0 deletions llvm/test/CodeGen/AMDGPU/scalar_to_vector.ll
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Expand Up @@ -332,3 +332,33 @@ define amdgpu_kernel void @scalar_to_vector_test6(ptr addrspace(1) %out, i8 zero
store <2 x half> %bc, ptr addrspace(1) %out
ret void
}

; bitcast (scalar_to_vector x) -> any_extend x
define i64 @bitcast_combine_scalar_to_vector_v4i16(i16 %arg) {
; SI-LABEL: bitcast_combine_scalar_to_vector_v4i16:
; SI: ; %bb.0:
; SI-NEXT: s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
; SI-NEXT: v_and_b32_e32 v1, 0xffff, v0
; SI-NEXT: v_and_b32_e32 v2, 0xff00, v0
; SI-NEXT: v_bfe_u32 v0, v0, 8, 8
; SI-NEXT: v_or_b32_e32 v2, v0, v2
; SI-NEXT: v_lshlrev_b32_e32 v3, 16, v2
; SI-NEXT: v_or_b32_e32 v0, v1, v3
; SI-NEXT: v_or_b32_e32 v1, v2, v3
; SI-NEXT: s_setpc_b64 s[30:31]
;
; GFX89-LABEL: bitcast_combine_scalar_to_vector_v4i16:
; GFX89: ; %bb.0:
; GFX89-NEXT: s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
; GFX89-NEXT: v_and_b32_e32 v1, 0xffffff00, v0
; GFX89-NEXT: v_or_b32_sdwa v1, v0, v1 dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:BYTE_1 src1_sel:DWORD
; GFX89-NEXT: v_lshlrev_b32_e32 v2, 16, v1
; GFX89-NEXT: v_or_b32_sdwa v1, v1, v2 dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_0 src1_sel:DWORD
; GFX89-NEXT: v_or_b32_sdwa v0, v0, v2 dst_sel:DWORD dst_unused:UNUSED_PAD src0_sel:WORD_0 src1_sel:DWORD
; GFX89-NEXT: s_setpc_b64 s[30:31]
%arg.cast = bitcast i16 %arg to <2 x i8>
%tmp1 = shufflevector <2 x i8> %arg.cast, <2 x i8> poison, <8 x i32> <i32 0, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1>
%tmp2 = shufflevector <8 x i8> %tmp1, <8 x i8> poison, <8 x i32> <i32 0, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison, i32 poison>
%cast = bitcast <8 x i8> %tmp2 to i64
ret i64 %cast
}
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