[llvm] r317499 - [PPC] Use xxbrd to speed up bswap64

[Guozhi Wei via llvm-commits]

Author: carrot
Date: Mon Nov  6 11:09:38 2017
New Revision: 317499

URL: http://llvm.org/viewvc/llvm-project?rev=317499&view=rev
Log:
[PPC] Use xxbrd to speed up bswap64

Power doesn't have bswap instructions, so llvm generates following code sequence for bswap64.

  rotldi   5, 3, 16
  rotldi   4, 3, 8
  rotldi   9, 3, 24
  rotldi   10, 3, 32
  rotldi   11, 3, 48
  rotldi   12, 3, 56
  rldimi 4, 5, 8, 48
  rldimi 4, 9, 16, 40
  rldimi 4, 10, 24, 32
  rldimi 4, 11, 40, 16
  rldimi 4, 12, 48, 8
  rldimi 4, 3, 56, 0

But Power9 has vector bswap instructions, they can also be used to speed up scalar bswap intrinsic. With this patch, bswap64 can be translated to:

  mtvsrdd 34, 3, 3
  xxbrd 34, 34
  mfvsrld 3, 34

Differential Revision: https://reviews.llvm.org/D39510


Added:
    llvm/trunk/test/CodeGen/PowerPC/bswap64.ll
Modified:
    llvm/trunk/lib/Target/PowerPC/PPCISelLowering.cpp
    llvm/trunk/lib/Target/PowerPC/PPCISelLowering.h

Modified: llvm/trunk/lib/Target/PowerPC/PPCISelLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/PowerPC/PPCISelLowering.cpp?rev=317499&r1=317498&r2=317499&view=diff
==============================================================================
--- llvm/trunk/lib/Target/PowerPC/PPCISelLowering.cpp (original)
+++ llvm/trunk/lib/Target/PowerPC/PPCISelLowering.cpp Mon Nov  6 11:09:38 2017
@@ -291,14 +291,16 @@ PPCTargetLowering::PPCTargetLowering(con
     setOperationAction(ISD::FROUND, MVT::f32, Legal);
   }
 
-  // PowerPC does not have BSWAP
+  // PowerPC does not have BSWAP, but we can use vector BSWAP instruction xxbrd
+  // to speed up scalar BSWAP64.
   // CTPOP or CTTZ were introduced in P8/P9 respectivelly
   setOperationAction(ISD::BSWAP, MVT::i32  , Expand);
-  setOperationAction(ISD::BSWAP, MVT::i64  , Expand);
   if (Subtarget.isISA3_0()) {
+    setOperationAction(ISD::BSWAP, MVT::i64  , Custom);
     setOperationAction(ISD::CTTZ , MVT::i32  , Legal);
     setOperationAction(ISD::CTTZ , MVT::i64  , Legal);
   } else {
+    setOperationAction(ISD::BSWAP, MVT::i64  , Expand);
     setOperationAction(ISD::CTTZ , MVT::i32  , Expand);
     setOperationAction(ISD::CTTZ , MVT::i64  , Expand);
   }
@@ -8675,6 +8677,23 @@ SDValue PPCTargetLowering::LowerREM(SDVa
   return Op;
 }
 
+// Lower scalar BSWAP64 to xxbrd.
+SDValue PPCTargetLowering::LowerBSWAP(SDValue Op, SelectionDAG &DAG) const {
+  SDLoc dl(Op);
+  // MTVSRDD
+  Op = DAG.getNode(ISD::BUILD_VECTOR, dl, MVT::v2i64, Op.getOperand(0),
+                   Op.getOperand(0));
+  // XXBRD
+  Op = DAG.getNode(PPCISD::XXREVERSE, dl, MVT::v2i64, Op);
+  // MFVSRD
+  int VectorIndex = 0;
+  if (Subtarget.isLittleEndian())
+    VectorIndex = 1;
+  Op = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, dl, MVT::i64, Op,
+                   DAG.getTargetConstant(VectorIndex, dl, MVT::i32));
+  return Op;
+}
+
 SDValue PPCTargetLowering::LowerSIGN_EXTEND_INREG(SDValue Op,
                                                   SelectionDAG &DAG) const {
   SDLoc dl(Op);
@@ -9146,6 +9165,8 @@ SDValue PPCTargetLowering::LowerOperatio
   case ISD::SREM:
   case ISD::UREM:
     return LowerREM(Op, DAG);
+  case ISD::BSWAP:
+    return LowerBSWAP(Op, DAG);
   }
 }
 

Modified: llvm/trunk/lib/Target/PowerPC/PPCISelLowering.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/PowerPC/PPCISelLowering.h?rev=317499&r1=317498&r2=317499&view=diff
==============================================================================
--- llvm/trunk/lib/Target/PowerPC/PPCISelLowering.h (original)
+++ llvm/trunk/lib/Target/PowerPC/PPCISelLowering.h Mon Nov  6 11:09:38 2017
@@ -953,6 +953,7 @@ namespace llvm {
     SDValue LowerINTRINSIC_WO_CHAIN(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerINTRINSIC_VOID(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerREM(SDValue Op, SelectionDAG &DAG) const;
+    SDValue LowerBSWAP(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerSCALAR_TO_VECTOR(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerSIGN_EXTEND_INREG(SDValue Op, SelectionDAG &DAG) const;
     SDValue LowerMUL(SDValue Op, SelectionDAG &DAG) const;

Added: llvm/trunk/test/CodeGen/PowerPC/bswap64.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/PowerPC/bswap64.ll?rev=317499&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/PowerPC/bswap64.ll (added)
+++ llvm/trunk/test/CodeGen/PowerPC/bswap64.ll Mon Nov  6 11:09:38 2017
@@ -0,0 +1,13 @@
+; RUN: llc -verify-machineinstrs < %s -mtriple=ppc64le-- -mcpu=pwr9 | FileCheck %s
+
+declare i64 @llvm.bswap.i64(i64)
+
+; CHECK: mtvsrdd
+; CHECK: xxbrd
+; CHECK: mfvsrd
+define i64 @bswap64(i64 %x) {
+entry:
+  %0 = call i64 @llvm.bswap.i64(i64 %x)
+  ret i64 %0
+}
+