[llvm] r372254 - [MIPS] For vectors, select `add %x, C` as `sub %x, -C` if it results in inline immediate
Roman Lebedev via llvm-commits
llvm-commits at lists.llvm.org
Wed Sep 18 12:34:41 PDT 2019
Author: lebedevri
Date: Wed Sep 18 12:34:41 2019
New Revision: 372254
URL: http://llvm.org/viewvc/llvm-project?rev=372254&view=rev
Log:
[MIPS] For vectors, select `add %x, C` as `sub %x, -C` if it results in inline immediate
Summary:
As discussed in https://reviews.llvm.org/D62341#1515637,
for MIPS `add %x, -1` isn't optimal. Unlike X86 there
are no fastpaths to matearialize such `-1`/`1` vector constants,
and `sub %x, 1` results in better codegen,
so undo canonicalization
Reviewers: atanasyan, Petar.Avramovic, RKSimon
Reviewed By: atanasyan
Subscribers: sdardis, arichardson, hiraditya, jrtc27, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D66805
Modified:
llvm/trunk/lib/Target/Mips/MipsISelDAGToDAG.cpp
llvm/trunk/lib/Target/Mips/MipsISelDAGToDAG.h
llvm/trunk/test/CodeGen/Mips/msa/arithmetic.ll
Modified: llvm/trunk/lib/Target/Mips/MipsISelDAGToDAG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/Mips/MipsISelDAGToDAG.cpp?rev=372254&r1=372253&r2=372254&view=diff
==============================================================================
--- llvm/trunk/lib/Target/Mips/MipsISelDAGToDAG.cpp (original)
+++ llvm/trunk/lib/Target/Mips/MipsISelDAGToDAG.cpp Wed Sep 18 12:34:41 2019
@@ -217,6 +217,51 @@ bool MipsDAGToDAGISel::selectVSplatMaskR
return false;
}
+/// Convert vector addition with vector subtraction if that allows to encode
+/// constant as an immediate and thus avoid extra 'ldi' instruction.
+/// add X, <-1, -1...> --> sub X, <1, 1...>
+bool MipsDAGToDAGISel::selectVecAddAsVecSubIfProfitable(SDNode *Node) {
+ assert(Node->getOpcode() == ISD::ADD && "Should only get 'add' here.");
+
+ EVT VT = Node->getValueType(0);
+ assert(VT.isVector() && "Should only be called for vectors.");
+
+ SDValue X = Node->getOperand(0);
+ SDValue C = Node->getOperand(1);
+
+ auto *BVN = dyn_cast<BuildVectorSDNode>(C);
+ if (!BVN)
+ return false;
+
+ APInt SplatValue, SplatUndef;
+ unsigned SplatBitSize;
+ bool HasAnyUndefs;
+
+ if (!BVN->isConstantSplat(SplatValue, SplatUndef, SplatBitSize, HasAnyUndefs,
+ 8, !Subtarget->isLittle()))
+ return false;
+
+ auto IsInlineConstant = [](const APInt &Imm) { return Imm.isIntN(5); };
+
+ if (IsInlineConstant(SplatValue))
+ return false; // Can already be encoded as an immediate.
+
+ APInt NegSplatValue = 0 - SplatValue;
+ if (!IsInlineConstant(NegSplatValue))
+ return false; // Even if we negate it it won't help.
+
+ SDLoc DL(Node);
+
+ SDValue NegC = CurDAG->FoldConstantArithmetic(
+ ISD::SUB, DL, VT, CurDAG->getConstant(0, DL, VT).getNode(), C.getNode());
+ assert(NegC && "Constant-folding failed!");
+ SDValue NewNode = CurDAG->getNode(ISD::SUB, DL, VT, X, NegC);
+
+ ReplaceNode(Node, NewNode.getNode());
+ SelectCode(NewNode.getNode());
+ return true;
+}
+
/// Select instructions not customized! Used for
/// expanded, promoted and normal instructions
void MipsDAGToDAGISel::Select(SDNode *Node) {
@@ -236,6 +281,12 @@ void MipsDAGToDAGISel::Select(SDNode *No
switch(Opcode) {
default: break;
+ case ISD::ADD:
+ if (Node->getSimpleValueType(0).isVector() &&
+ selectVecAddAsVecSubIfProfitable(Node))
+ return;
+ break;
+
// Get target GOT address.
case ISD::GLOBAL_OFFSET_TABLE:
ReplaceNode(Node, getGlobalBaseReg());
Modified: llvm/trunk/lib/Target/Mips/MipsISelDAGToDAG.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/Mips/MipsISelDAGToDAG.h?rev=372254&r1=372253&r2=372254&view=diff
==============================================================================
--- llvm/trunk/lib/Target/Mips/MipsISelDAGToDAG.h (original)
+++ llvm/trunk/lib/Target/Mips/MipsISelDAGToDAG.h Wed Sep 18 12:34:41 2019
@@ -125,6 +125,11 @@ private:
/// starting at bit zero.
virtual bool selectVSplatMaskR(SDValue N, SDValue &Imm) const;
+ /// Convert vector addition with vector subtraction if that allows to encode
+ /// constant as an immediate and thus avoid extra 'ldi' instruction.
+ /// add X, <-1, -1...> --> sub X, <1, 1...>
+ bool selectVecAddAsVecSubIfProfitable(SDNode *Node);
+
void Select(SDNode *N) override;
virtual bool trySelect(SDNode *Node) = 0;
Modified: llvm/trunk/test/CodeGen/Mips/msa/arithmetic.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/Mips/msa/arithmetic.ll?rev=372254&r1=372253&r2=372254&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/Mips/msa/arithmetic.ll (original)
+++ llvm/trunk/test/CodeGen/Mips/msa/arithmetic.ll Wed Sep 18 12:34:41 2019
@@ -194,8 +194,7 @@ define void @sub_v16i8_i_negated(<16 x i
; ALL-LABEL: sub_v16i8_i_negated:
; ALL: # %bb.0:
; ALL-NEXT: ld.b $w0, 0($5)
-; ALL-NEXT: ldi.b $w1, -1
-; ALL-NEXT: addv.b $w0, $w0, $w1
+; ALL-NEXT: subvi.b $w0, $w0, 1
; ALL-NEXT: jr $ra
; ALL-NEXT: st.b $w0, 0($4)
%1 = load <16 x i8>, <16 x i8>* %a
@@ -222,9 +221,8 @@ define void @sub_v8i16_i(<8 x i16>* %c,
define void @sub_v8i16_i_negated(<8 x i16>* %c, <8 x i16>* %a) nounwind {
; ALL-LABEL: sub_v8i16_i_negated:
; ALL: # %bb.0:
-; ALL-NEXT: ldi.b $w0, -1
-; ALL-NEXT: ld.h $w1, 0($5)
-; ALL-NEXT: addv.h $w0, $w1, $w0
+; ALL-NEXT: ld.h $w0, 0($5)
+; ALL-NEXT: subvi.h $w0, $w0, 1
; ALL-NEXT: jr $ra
; ALL-NEXT: st.h $w0, 0($4)
%1 = load <8 x i16>, <8 x i16>* %a
@@ -250,9 +248,8 @@ define void @sub_v4i32_i(<4 x i32>* %c,
define void @sub_v4i32_i_negated(<4 x i32>* %c, <4 x i32>* %a) nounwind {
; ALL-LABEL: sub_v4i32_i_negated:
; ALL: # %bb.0:
-; ALL-NEXT: ldi.b $w0, -1
-; ALL-NEXT: ld.w $w1, 0($5)
-; ALL-NEXT: addv.w $w0, $w1, $w0
+; ALL-NEXT: ld.w $w0, 0($5)
+; ALL-NEXT: subvi.w $w0, $w0, 1
; ALL-NEXT: jr $ra
; ALL-NEXT: st.w $w0, 0($4)
%1 = load <4 x i32>, <4 x i32>* %a
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