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AMDGPU: Handle partial shift reduction for variable shifts 

If the variable shift amount has known bits, we can still reduce
the shift.

llvm-svn: 331917
This commit is contained in:
Matt Arsenault 2018-05-09 20:52:54 +00:00
parent b143d9a5ea
commit 74fd7600d2
2 changed files with 57 additions and 14 deletions
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23
llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp
View File

@ -3154,22 +3154,29 @@ SDValue AMDGPUTargetLowering::performTruncateCombine(
(Src.getOpcode() == ISD::SRL ||
Src.getOpcode() == ISD::SRA ||
Src.getOpcode() == ISD::SHL)) {
if (auto ShiftAmount = isConstOrConstSplat(Src.getOperand(1))) {
if (ShiftAmount->getZExtValue() <= VT.getScalarSizeInBits()) {
SDValue Amt = Src.getOperand(1);
KnownBits Known;
DAG.computeKnownBits(Amt, Known);
unsigned Size = VT.getScalarSizeInBits();
if ((Known.isConstant() && Known.getConstant().ule(Size)) ||
(Known.getBitWidth() - Known.countMinLeadingZeros() <= Log2_32(Size))) {
EVT MidVT = VT.isVector() ?
EVT::getVectorVT(*DAG.getContext(), MVT::i32,
VT.getVectorNumElements()) : MVT::i32;
EVT ShiftTy = getShiftAmountTy(MidVT, DAG.getDataLayout());
SDValue NewShiftAmt = DAG.getConstant(ShiftAmount->getZExtValue(),
SL, ShiftTy);
EVT NewShiftVT = getShiftAmountTy(MidVT, DAG.getDataLayout());
SDValue Trunc = DAG.getNode(ISD::TRUNCATE, SL, MidVT,
Src.getOperand(0));
DCI.AddToWorklist(Trunc.getNode());
SDValue ShrunkShift = DAG.getNode(Src.getOpcode(), SL, MidVT,
Trunc, NewShiftAmt);
return DAG.getNode(ISD::TRUNCATE, SL, VT, ShrunkShift);
if (Amt.getValueType() != NewShiftVT) {
Amt = DAG.getZExtOrTrunc(Amt, SL, NewShiftVT);
DCI.AddToWorklist(Amt.getNode());
}
SDValue ShrunkShift = DAG.getNode(Src.getOpcode(), SL, MidVT,
Trunc, Amt);
return DAG.getNode(ISD::TRUNCATE, SL, VT, ShrunkShift);
}
}
}

36
llvm/test/CodeGen/AMDGPU/partial-shift-shrink.ll
View File

@ -100,3 +100,39 @@ define amdgpu_kernel void @s_trunc_srl_i64_16_to_i16(i64 %x) {
store i16 %add, i16 addrspace(1)* undef
ret void
}
; GCN-LABEL: {{^}}trunc_srl_i64_var_mask15_to_i16:
; GCN: s_waitcnt
; GCN-NEXT: v_and_b32_e32 v1, 15, v2
; GCN-NEXT: v_lshrrev_b32_e32 v0, v1, v0
; GCN-NEXT: s_setpc_b64
define i16 @trunc_srl_i64_var_mask15_to_i16(i64 %x, i64 %amt) {
%amt.masked = and i64 %amt, 15
%shift = lshr i64 %x, %amt.masked
%trunc = trunc i64 %shift to i16
ret i16 %trunc
}
; GCN-LABEL: {{^}}trunc_srl_i64_var_mask16_to_i16:
; GCN: s_waitcnt
; GCN-NEXT: v_and_b32_e32 v2, 16, v2
; GCN-NEXT: v_lshrrev_b64 v[0:1], v2, v[0:1]
; GCN-NEXT: s_setpc_b64
define i16 @trunc_srl_i64_var_mask16_to_i16(i64 %x, i64 %amt) {
%amt.masked = and i64 %amt, 16
%shift = lshr i64 %x, %amt.masked
%trunc = trunc i64 %shift to i16
ret i16 %trunc
}
; GCN-LABEL: {{^}}trunc_srl_i64_var_mask31_to_i16:
; GCN: s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
; GCN-NEXT: v_and_b32_e32 v2, 31, v2
; GCN-NEXT: v_lshrrev_b64 v[0:1], v2, v[0:1]
; GCN-NEXT: s_setpc_b64 s[30:31]
define i16 @trunc_srl_i64_var_mask31_to_i16(i64 %x, i64 %amt) {
%amt.masked = and i64 %amt, 31
%shift = lshr i64 %x, %amt.masked
%trunc = trunc i64 %shift to i16
ret i16 %trunc
}