[llvm] a41ea78 - [SelectionDAG] Enable CTPOP optimization fine tuning
David Zarzycki via llvm-commits
llvm-commits at lists.llvm.org
Mon Nov 9 10:49:37 PST 2020
Author: David Zarzycki
Date: 2020-11-09T13:49:01-05:00
New Revision: a41ea782c8e1273af4a39a647e41d6f0f42c3411
URL: https://github.com/llvm/llvm-project/commit/a41ea782c8e1273af4a39a647e41d6f0f42c3411
DIFF: https://github.com/llvm/llvm-project/commit/a41ea782c8e1273af4a39a647e41d6f0f42c3411.diff
LOG: [SelectionDAG] Enable CTPOP optimization fine tuning
Add a TLI hook to allow SelectionDAG to fine tune the conversion of CTPOP to a chain of "x & (x - 1)" when CTPOP isn't legal.
A subsequent patch will attempt to fine tune the X86 code gen.
Reviewed By: spatel
Differential Revision: https://reviews.llvm.org/D89952
Added:
Modified:
llvm/include/llvm/CodeGen/TargetLowering.h
llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
Removed:
################################################################################
diff --git a/llvm/include/llvm/CodeGen/TargetLowering.h b/llvm/include/llvm/CodeGen/TargetLowering.h
index 8922c9b8db78..af7984b426ee 100644
--- a/llvm/include/llvm/CodeGen/TargetLowering.h
+++ b/llvm/include/llvm/CodeGen/TargetLowering.h
@@ -605,6 +605,12 @@ class TargetLoweringBase {
return false;
}
+ /// Return the maximum number of "x & (x - 1)" operations that can be done
+ /// instead of deferring to a custom CTPOP.
+ virtual unsigned getCustomCtpopCost(EVT VT, ISD::CondCode Cond) const {
+ return 1;
+ }
+
/// Return true if instruction generated for equality comparison is folded
/// with instruction generated for signed comparison.
virtual bool isEqualityCmpFoldedWithSignedCmp() const { return true; }
diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index d4ad5cb27a37..9d62faf7d956 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -3403,15 +3403,23 @@ static SDValue simplifySetCCWithCTPOP(const TargetLowering &TLI, EVT VT,
// (ctpop x) u< 2 -> (x & x-1) == 0
// (ctpop x) u> 1 -> (x & x-1) != 0
- if ((Cond == ISD::SETULT && C1 == 2) || (Cond == ISD::SETUGT && C1 == 1)) {
- // This based on X86's custom lowering for vector CTPOP which produces more
- // instructions than the expansion here.
+ if (Cond == ISD::SETULT || Cond == ISD::SETUGT) {
+ unsigned CostLimit = TLI.getCustomCtpopCost(CTVT, Cond);
+ if (C1.ugt(CostLimit + (Cond == ISD::SETULT)))
+ return SDValue();
+ if (C1 == 0 && (Cond == ISD::SETULT))
+ return SDValue(); // This is handled elsewhere.
+
+ unsigned Passes = C1.getLimitedValue() - (Cond == ISD::SETULT);
SDValue NegOne = DAG.getAllOnesConstant(dl, CTVT);
- SDValue Add = DAG.getNode(ISD::ADD, dl, CTVT, CTOp, NegOne);
- SDValue And = DAG.getNode(ISD::AND, dl, CTVT, CTOp, Add);
+ SDValue Result = CTOp;
+ for (unsigned i = 0; i < Passes; i++) {
+ SDValue Add = DAG.getNode(ISD::ADD, dl, CTVT, Result, NegOne);
+ Result = DAG.getNode(ISD::AND, dl, CTVT, Result, Add);
+ }
ISD::CondCode CC = Cond == ISD::SETULT ? ISD::SETEQ : ISD::SETNE;
- return DAG.getSetCC(dl, VT, And, DAG.getConstant(0, dl, CTVT), CC);
+ return DAG.getSetCC(dl, VT, Result, DAG.getConstant(0, dl, CTVT), CC);
}
// If ctpop is not supported, expand a power-of-2 comparison based on it.
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