[SystemZ] Extend memcmp support to all constant lengths

This uses the infrastructure added for memcpy and memmove in r189331.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189458 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 92 insertions, 26 deletions

diff --git a/lib/Target/SystemZ/SystemZISelLowering.cpp b/lib/Target/SystemZ/SystemZISelLowering.cpp
index 216ca3450c..dd230c62a5 100644
--- a/lib/Target/SystemZ/SystemZISelLowering.cpp
+++ b/lib/Target/SystemZ/SystemZISelLowering.cpp
@@ -1954,6 +1954,18 @@ static MachineBasicBlock *emitBlockAfter(MachineBasicBlock *MBB) {
   return NewMBB;
 }
 
+// Split MBB after MI and return the new block (the one that contains
+// instructions after MI).
+static MachineBasicBlock *splitBlockAfter(MachineInstr *MI,
+                                          MachineBasicBlock *MBB) {
+  MachineBasicBlock *NewMBB = emitBlockAfter(MBB);
+  NewMBB->splice(NewMBB->begin(), MBB,
+                 llvm::next(MachineBasicBlock::iterator(MI)),
+                 MBB->end());
+  NewMBB->transferSuccessorsAndUpdatePHIs(MBB);
+  return NewMBB;
+}
+
 // Split MBB before MI and return the new block (the one that contains MI).
 static MachineBasicBlock *splitBlockBefore(MachineInstr *MI,
                                            MachineBasicBlock *MBB) {
@@ -2490,6 +2502,11 @@ SystemZTargetLowering::emitMemMemWrapper(MachineInstr *MI,
   uint64_t       SrcDisp  = MI->getOperand(3).getImm();
   uint64_t       Length   = MI->getOperand(4).getImm();
 
+  // When generating more than one CLC, all but the last will need to
+  // branch to the end when a difference is found.
+  MachineBasicBlock *EndMBB = (Length > 256 && Opcode == SystemZ::CLC ?
+                               splitBlockAfter(MI, MBB) : 0);
+
   // Check for the loop form, in which operand 5 is the trip count.
   if (MI->getNumExplicitOperands() > 5) {
     bool HaveSingleBase = DestBase.isIdenticalTo(SrcBase);
@@ -2514,6 +2531,7 @@ SystemZTargetLowering::emitMemMemWrapper(MachineInstr *MI,
     MachineBasicBlock *StartMBB = MBB;
     MachineBasicBlock *DoneMBB = splitBlockBefore(MI, MBB);
     MachineBasicBlock *LoopMBB = emitBlockAfter(StartMBB);
+    MachineBasicBlock *NextMBB = (EndMBB ? emitBlockAfter(LoopMBB) : LoopMBB);
 
     //  StartMBB:
     //   # fall through to LoopMMB
@@ -2521,39 +2539,54 @@ SystemZTargetLowering::emitMemMemWrapper(MachineInstr *MI,
 
     //  LoopMBB:
     //   %ThisDestReg = phi [ %StartDestReg, StartMBB ],
-    //                      [ %NextDestReg, LoopMBB ]
+    //                      [ %NextDestReg, NextMBB ]
     //   %ThisSrcReg = phi [ %StartSrcReg, StartMBB ],
-    //                     [ %NextSrcReg, LoopMBB ]
+    //                     [ %NextSrcReg, NextMBB ]
     //   %ThisCountReg = phi [ %StartCountReg, StartMBB ],
-    //                       [ %NextCountReg, LoopMBB ]
-    //   PFD 2, 768+DestDisp(%ThisDestReg)
+    //                       [ %NextCountReg, NextMBB ]
+    //   ( PFD 2, 768+DestDisp(%ThisDestReg) )
     //   Opcode DestDisp(256,%ThisDestReg), SrcDisp(%ThisSrcReg)
-    //   %NextDestReg = LA 256(%ThisDestReg)
-    //   %NextSrcReg = LA 256(%ThisSrcReg)
-    //   %NextCountReg = AGHI %ThisCountReg, -1
-    //   CGHI %NextCountReg, 0
-    //   JLH LoopMBB
-    //   # fall through to DoneMMB
+    //   ( JLH EndMBB )
     //
-    // The AGHI, CGHI and JLH should be converted to BRCTG by later passes.
+    // The prefetch is used only for MVC.  The JLH is used only for CLC.
     MBB = LoopMBB;
 
     BuildMI(MBB, DL, TII->get(SystemZ::PHI), ThisDestReg)
       .addReg(StartDestReg).addMBB(StartMBB)
-      .addReg(NextDestReg).addMBB(LoopMBB);
+      .addReg(NextDestReg).addMBB(NextMBB);
     if (!HaveSingleBase)
       BuildMI(MBB, DL, TII->get(SystemZ::PHI), ThisSrcReg)
         .addReg(StartSrcReg).addMBB(StartMBB)
-        .addReg(NextSrcReg).addMBB(LoopMBB);
+        .addReg(NextSrcReg).addMBB(NextMBB);
     BuildMI(MBB, DL, TII->get(SystemZ::PHI), ThisCountReg)
       .addReg(StartCountReg).addMBB(StartMBB)
-      .addReg(NextCountReg).addMBB(LoopMBB);
-    BuildMI(MBB, DL, TII->get(SystemZ::PFD))
-      .addImm(SystemZ::PFD_WRITE)
-      .addReg(ThisDestReg).addImm(DestDisp + 768).addReg(0);
+      .addReg(NextCountReg).addMBB(NextMBB);
+    if (Opcode == SystemZ::MVC)
+      BuildMI(MBB, DL, TII->get(SystemZ::PFD))
+        .addImm(SystemZ::PFD_WRITE)
+        .addReg(ThisDestReg).addImm(DestDisp + 768).addReg(0);
     BuildMI(MBB, DL, TII->get(Opcode))
       .addReg(ThisDestReg).addImm(DestDisp).addImm(256)
       .addReg(ThisSrcReg).addImm(SrcDisp);
+    if (EndMBB) {
+      BuildMI(MBB, DL, TII->get(SystemZ::BRC))
+        .addImm(SystemZ::CCMASK_ICMP).addImm(SystemZ::CCMASK_CMP_NE)
+        .addMBB(EndMBB);
+      MBB->addSuccessor(EndMBB);
+      MBB->addSuccessor(NextMBB);
+    }
+
+    // NextMBB:
+    //   %NextDestReg = LA 256(%ThisDestReg)
+    //   %NextSrcReg = LA 256(%ThisSrcReg)
+    //   %NextCountReg = AGHI %ThisCountReg, -1
+    //   CGHI %NextCountReg, 0
+    //   JLH LoopMBB
+    //   # fall through to DoneMMB
+    //
+    // The AGHI, CGHI and JLH should be converted to BRCTG by later passes.
+    MBB = NextMBB;
+
     BuildMI(MBB, DL, TII->get(SystemZ::LA), NextDestReg)
       .addReg(ThisDestReg).addImm(256).addReg(0);
     if (!HaveSingleBase)
@@ -2599,6 +2632,22 @@ SystemZTargetLowering::emitMemMemWrapper(MachineInstr *MI,
     DestDisp += ThisLength;
     SrcDisp += ThisLength;
     Length -= ThisLength;
+    // If there's another CLC to go, branch to the end if a difference
+    // was found.
+    if (EndMBB && Length > 0) {
+      MachineBasicBlock *NextMBB = splitBlockBefore(MI, MBB);
+      BuildMI(MBB, DL, TII->get(SystemZ::BRC))
+        .addImm(SystemZ::CCMASK_ICMP).addImm(SystemZ::CCMASK_CMP_NE)
+        .addMBB(EndMBB);
+      MBB->addSuccessor(EndMBB);
+      MBB->addSuccessor(NextMBB);
+      MBB = NextMBB;
+    }
+  }
+  if (EndMBB) {
+    MBB->addSuccessor(EndMBB);
+    MBB = EndMBB;
+    MBB->addLiveIn(SystemZ::CC);
   }
 
   MI->eraseFromParent();
diff --git a/lib/Target/SystemZ/SystemZSelectionDAGInfo.cpp b/lib/Target/SystemZ/SystemZSelectionDAGInfo.cpp
index 6026b1f6f0..dc2f225acb 100644
--- a/lib/Target/SystemZ/SystemZSelectionDAGInfo.cpp
+++ b/lib/Target/SystemZ/SystemZSelectionDAGInfo.cpp
@@ -141,6 +141,28 @@ EmitTargetCodeForMemset(SelectionDAG &DAG, SDLoc DL, SDValue Chain,
   return SDValue();
 }
 
+// Use CLC to compare [Src1, Src1 + Size) with [Src2, Src2 + Size),
+// deciding whether to use a loop or straight-line code.
+static SDValue emitCLC(SelectionDAG &DAG, SDLoc DL, SDValue Chain,
+                       SDValue Src1, SDValue Src2, uint64_t Size) {
+  SDVTList VTs = DAG.getVTList(MVT::Other, MVT::Glue);
+  EVT PtrVT = Src1.getValueType();
+  // A two-CLC sequence is a clear win over a loop, not least because it
+  // needs only one branch.  A three-CLC sequence needs the same number
+  // of branches as a loop (i.e. 2), but is shorter.  That brings us to
+  // lengths greater than 768 bytes.  It seems relatively likely that
+  // a difference will be found within the first 768 bytes, so we just
+  // optimize for the smallest number of branch instructions, in order
+  // to avoid polluting the prediction buffer too much.  A loop only ever
+  // needs 2 branches, whereas a straight-line sequence would need 3 or more.
+  if (Size > 3 * 256)
+    return DAG.getNode(SystemZISD::CLC_LOOP, DL, VTs, Chain, Src1, Src2,
+                       DAG.getConstant(Size, PtrVT),
+                       DAG.getConstant(Size / 256, PtrVT));
+  return DAG.getNode(SystemZISD::CLC, DL, VTs, Chain, Src1, Src2,
+                     DAG.getConstant(Size, PtrVT));
+}
+
 // Convert the current CC value into an integer that is 0 if CC == 0,
 // less than zero if CC == 1 and greater than zero if CC >= 2.
 // The sequence starts with IPM, which puts CC into bits 29 and 28
@@ -159,17 +181,12 @@ EmitTargetCodeForMemcmp(SelectionDAG &DAG, SDLoc DL, SDValue Chain,
                         SDValue Src1, SDValue Src2, SDValue Size,
                         MachinePointerInfo Op1PtrInfo,
                         MachinePointerInfo Op2PtrInfo) const {
-  EVT PtrVT = Src1.getValueType();
   if (ConstantSDNode *CSize = dyn_cast<ConstantSDNode>(Size)) {
     uint64_t Bytes = CSize->getZExtValue();
-    if (Bytes >= 1 && Bytes <= 0x100) {
-      // A single CLC.
-      SDVTList VTs = DAG.getVTList(MVT::Other, MVT::Glue);
-      Chain = DAG.getNode(SystemZISD::CLC, DL, VTs, Chain,
-                          Src1, Src2, Size, DAG.getConstant(0, PtrVT));
-      SDValue Glue = Chain.getValue(1);
-      return std::make_pair(addIPMSequence(DL, Glue, DAG), Chain);
-    }
+    assert(Bytes > 0 && "Caller should have handled 0-size case");
+    Chain = emitCLC(DAG, DL, Chain, Src1, Src2, Bytes);
+    SDValue Glue = Chain.getValue(1);
+    return std::make_pair(addIPMSequence(DL, Glue, DAG), Chain);
   }
   return std::make_pair(SDValue(), SDValue());
 }