[mips] For indirect calls we don't need $gp to point to .got.

[sstankovic]

Summary

Mips linker doesn't generate lazy binding stub for a function whose address is taken in the program.

[dsanders]

lib/Target/Mips/MipsISelLowering.cpp

2425

I agree that this is equivalent, but is it possible to test for MO_GOT_CALL instead of the conditions that lead to choosing MO_GOT_CALL?

test/CodeGen/Mips/prevent-hoisting.ll

13–26

This is just fixing up a test where the instructions changed order isn't it?

If so, I feel that there ought to be a more robust way of testing for this. This is close:

CHECK-NEXT: {{BB[0-9_#]+}}:
CHECK-DAG: sll $1, $[[R0:[0-9]+]], 4
CHECK: {{BB[0-9_#]+}}:
CHECK: [[BB0]]:

but there's no guarantee that there will be a second basic block between the two.

If neither of us can think of anything better, then we should go ahead with this change as-is and maintain it when necessary.

[sstankovic]

The patch is updated.

[sstankovic]

lib/Target/Mips/MipsISelLowering.cpp

2425

Done.

test/CodeGen/Mips/prevent-hoisting.ll

13–26

This is just fixing up a test where the instructions changed order isn't it?

Yes. Currently the following sequence is generated at the start of two blocks:

sll     $1, $2, 4
sll     $2, $2, 6
addu    $1, $2, $1
lw      $2, %got(assignSE2partition)($16)

CHECK-NEXT checks only for the first instruction (it checks for instructions up to the first one that changes $at, which in this case is the first instruction). After the patch is applied, there are the same 4 instructions at the start of two blocks, but reordered:

lw      $2, %got(assignSE2partition)($2)
sll     $1, $3, 4
sll     $3, $3, 6
addu    $1, $3, $1

CHECK-NEXTs in the patch now check for first two instructions. Adding CHECK-DAG for all 4 instructions would protect from reordering, but the test must also make sure that all 4 instructions are at the start of the block, and I think that's not possible to do when DAG is used (that is, to combine DAG and NEXT).

[dsanders]

Thanks. I still can't think of a better way to update prevent-hoisting.ll so: LGTM

[sstankovic]

Closed by commit rL218744 (authored by @sstankovic).

lib/Target/Mips/Mips16ISelLowering.h

private:
 
     const char *getMips16HelperFunction
       (Type* RetTy, ArgListTy &Args, bool &needHelper) const;
 
     void
     getOpndList(SmallVectorImpl<SDValue> &Ops,
                 std::deque< std::pair<unsigned, SDValue> > &RegsToPass,
                 bool IsPICCall, bool GlobalOrExternal, bool InternalLinkage,
-                CallLoweringInfo &CLI, SDValue Callee,
+                bool IsCallReloc, CallLoweringInfo &CLI, SDValue Callee,
                 SDValue Chain) const override;
 
     MachineBasicBlock *emitSel16(unsigned Opc, MachineInstr *MI,
                                  MachineBasicBlock *BB) const;
 
     MachineBasicBlock *emitSeliT16(unsigned Opc1, unsigned Opc2,
                                    MachineInstr *MI,
                                    MachineBasicBlock *BB) const;

lib/Target/Mips/Mips16ISelLowering.cpp

#endif
   needHelper = true;
   return result;
 }
 
 void Mips16TargetLowering::
 getOpndList(SmallVectorImpl<SDValue> &Ops,
             std::deque< std::pair<unsigned, SDValue> > &RegsToPass,
             bool IsPICCall, bool GlobalOrExternal, bool InternalLinkage,
-            CallLoweringInfo &CLI, SDValue Callee, SDValue Chain) const {
+            bool IsCallReloc, CallLoweringInfo &CLI, SDValue Callee,
+            SDValue Chain) const {
   SelectionDAG &DAG = CLI.DAG;
   MachineFunction &MF = DAG.getMachineFunction();
   MipsFunctionInfo *FuncInfo = MF.getInfo<MipsFunctionInfo>();
   const char* Mips16HelperFunction = nullptr;
   bool NeedMips16Helper = false;
 
   if (Subtarget.inMips16HardFloat()) {
     //
if (NeedMips16Helper) {
                                  FuncInfo->callPtrInfo(S->getSymbol()));
     } else
       RegsToPass.push_front(std::make_pair((unsigned)Mips::T9, Callee));
   }
 
   Ops.push_back(JumpTarget);
 
   MipsTargetLowering::getOpndList(Ops, RegsToPass, IsPICCall, GlobalOrExternal,
-                                  InternalLinkage, CLI, Callee, Chain);
+                                  InternalLinkage, IsCallReloc, CLI, Callee,
+                                  Chain);
 }
 
 MachineBasicBlock *Mips16TargetLowering::
 emitSel16(unsigned Opc, MachineInstr *MI, MachineBasicBlock *BB) const {
   if (DontExpandCondPseudos16)
     return BB;
   const TargetInstrInfo *TII =
       getTargetMachine().getSubtargetImpl()->getInstrInfo();

lib/Target/Mips/MipsISelLowering.h

protected:
 
     /// This function fills Ops, which is the list of operands that will later
     /// be used when a function call node is created. It also generates
     /// copyToReg nodes to set up argument registers.
     virtual void
     getOpndList(SmallVectorImpl<SDValue> &Ops,
                 std::deque< std::pair<unsigned, SDValue> > &RegsToPass,
                 bool IsPICCall, bool GlobalOrExternal, bool InternalLinkage,
-                CallLoweringInfo &CLI, SDValue Callee, SDValue Chain) const;
+                bool IsCallReloc, CallLoweringInfo &CLI, SDValue Callee,
+                SDValue Chain) const;
 
     /// ByValArgInfo - Byval argument information.
     struct ByValArgInfo {
       unsigned FirstIdx; // Index of the first register used.
       unsigned NumRegs;  // Number of registers used for this argument.
       unsigned Address;  // Offset of the stack area used to pass this argument.
 
       ByValArgInfo() : FirstIdx(0), NumRegs(0), Address(0) {}

lib/Target/Mips/MipsISelLowering.cpp

MipsTargetLowering::passArgOnStack(SDValue StackPtr, unsigned Offset,
   return DAG.getStore(Chain, DL, Arg, FIN, MachinePointerInfo(),
                       /*isVolatile=*/ true, false, 0);
 }
 
 void MipsTargetLowering::
 getOpndList(SmallVectorImpl<SDValue> &Ops,
             std::deque< std::pair<unsigned, SDValue> > &RegsToPass,
             bool IsPICCall, bool GlobalOrExternal, bool InternalLinkage,
-            CallLoweringInfo &CLI, SDValue Callee, SDValue Chain) const {
+            bool IsCallReloc, CallLoweringInfo &CLI, SDValue Callee,
+            SDValue Chain) const {
   // Insert node "GP copy globalreg" before call to function.
   //
   // R_MIPS_CALL* operators (emitted when non-internal functions are called
   // in PIC mode) allow symbols to be resolved via lazy binding.
   // The lazy binding stub requires GP to point to the GOT.
-  if (IsPICCall && !InternalLinkage) {
+  // Note that we don't need GP to point to the GOT for indirect calls
+  // (when R_MIPS_CALL* is not used for the call) because Mips linker generates
+  // lazy binding stub for a function only when R_MIPS_CALL* are the only relocs
+  // used for the function (that is, Mips linker doesn't generate lazy binding
+  // stub for a function whose address is taken in the program).
+  if (IsPICCall && !InternalLinkage && IsCallReloc) {
     unsigned GPReg = Subtarget.isABI_N64() ? Mips::GP_64 : Mips::GP;
     EVT Ty = Subtarget.isABI_N64() ? MVT::i64 : MVT::i32;
     RegsToPass.push_back(std::make_pair(GPReg, getGlobalReg(CLI.DAG, Ty)));
   }
 
   // Build a sequence of copy-to-reg nodes chained together with token
   // chain and flag operands which copy the outgoing args into registers.
   // The InFlag in necessary since all emitted instructions must be
   // stuck together.
if (!MemOpChains.empty())
     Chain = DAG.getNode(ISD::TokenFactor, DL, MVT::Other, MemOpChains);
 
   // If the callee is a GlobalAddress/ExternalSymbol node (quite common, every
   // direct call is) turn it into a TargetGlobalAddress/TargetExternalSymbol
   // node so that legalize doesn't hack it.
   bool IsPICCall =
       (Subtarget.isABI_N64() || IsPIC); // true if calls are translated to
                                          // jalr $25
-  bool GlobalOrExternal = false, InternalLinkage = false;
+  bool GlobalOrExternal = false, InternalLinkage = false, IsCallReloc = false;
   SDValue CalleeLo;
   EVT Ty = Callee.getValueType();
 
   if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee)) {
     if (IsPICCall) {
       const GlobalValue *Val = G->getGlobal();
       InternalLinkage = Val->hasInternalLinkage();
 
       if (InternalLinkage)
         Callee = getAddrLocal(G, Ty, DAG,
                               Subtarget.isABI_N32() || Subtarget.isABI_N64());
-      else if (LargeGOT)
+      else if (LargeGOT) {
         Callee = getAddrGlobalLargeGOT(G, Ty, DAG, MipsII::MO_CALL_HI16,
                                        MipsII::MO_CALL_LO16, Chain,
                                        FuncInfo->callPtrInfo(Val));
-      else
+        IsCallReloc = true;
+      } else {
         Callee = getAddrGlobal(G, Ty, DAG, MipsII::MO_GOT_CALL, Chain,
                                FuncInfo->callPtrInfo(Val));
+        IsCallReloc = true;
+      }
     } else
       Callee = DAG.getTargetGlobalAddress(G->getGlobal(), DL, getPointerTy(), 0,
                                           MipsII::MO_NO_FLAG);
     GlobalOrExternal = true;
   }
   else if (ExternalSymbolSDNode *S = dyn_cast<ExternalSymbolSDNode>(Callee)) {
     const char *Sym = S->getSymbol();
 
     if (!Subtarget.isABI_N64() && !IsPIC) // !N64 && static
       Callee = DAG.getTargetExternalSymbol(Sym, getPointerTy(),
                                             MipsII::MO_NO_FLAG);
-    else if (LargeGOT)
+    else if (LargeGOT) {
       Callee = getAddrGlobalLargeGOT(S, Ty, DAG, MipsII::MO_CALL_HI16,
                                      MipsII::MO_CALL_LO16, Chain,
                                      FuncInfo->callPtrInfo(Sym));
-    else // N64 || PIC
+      IsCallReloc = true;
+    } else { // N64 || PIC
       Callee = getAddrGlobal(S, Ty, DAG, MipsII::MO_GOT_CALL, Chain,
                              FuncInfo->callPtrInfo(Sym));
+      IsCallReloc = true;
+    }
 
     GlobalOrExternal = true;
   }
 
   SmallVector<SDValue, 8> Ops(1, Chain);
   SDVTList NodeTys = DAG.getVTList(MVT::Other, MVT::Glue);
 
   getOpndList(Ops, RegsToPass, IsPICCall, GlobalOrExternal, InternalLinkage,
-              CLI, Callee, Chain);
+              IsCallReloc, CLI, Callee, Chain);
 
   if (IsTailCall)
     return DAG.getNode(MipsISD::TailCall, DL, MVT::Other, Ops);
 
   Chain = DAG.getNode(MipsISD::JmpLink, DL, NodeTys, Ops);
   SDValue InFlag = Chain.getValue(1);
 
   // Create the CALLSEQ_END node.

lib/Target/Mips/MipsSEISelLowering.h

private:
     bool isEligibleForTailCallOptimization(const MipsCC &MipsCCInfo,
                                      unsigned NextStackOffset,
                                      const MipsFunctionInfo& FI) const override;
 
     void
     getOpndList(SmallVectorImpl<SDValue> &Ops,
                 std::deque< std::pair<unsigned, SDValue> > &RegsToPass,
                 bool IsPICCall, bool GlobalOrExternal, bool InternalLinkage,
-                CallLoweringInfo &CLI, SDValue Callee,
+                bool IsCallReloc, CallLoweringInfo &CLI, SDValue Callee,
                 SDValue Chain) const override;
 
     SDValue lowerLOAD(SDValue Op, SelectionDAG &DAG) const;
     SDValue lowerSTORE(SDValue Op, SelectionDAG &DAG) const;
 
     SDValue lowerMulDiv(SDValue Op, unsigned NewOpc, bool HasLo, bool HasHi,
                         SelectionDAG &DAG) const;
 

lib/Target/Mips/MipsSEISelLowering.cpp

isEligibleForTailCallOptimization(const MipsCC &MipsCCInfo,
   // caller's.
   return NextStackOffset <= FI.getIncomingArgSize();
 }
 
 void MipsSETargetLowering::
 getOpndList(SmallVectorImpl<SDValue> &Ops,
             std::deque< std::pair<unsigned, SDValue> > &RegsToPass,
             bool IsPICCall, bool GlobalOrExternal, bool InternalLinkage,
-            CallLoweringInfo &CLI, SDValue Callee, SDValue Chain) const {
+            bool IsCallReloc, CallLoweringInfo &CLI, SDValue Callee,
+            SDValue Chain) const {
   Ops.push_back(Callee);
   MipsTargetLowering::getOpndList(Ops, RegsToPass, IsPICCall, GlobalOrExternal,
-                                  InternalLinkage, CLI, Callee, Chain);
+                                  InternalLinkage, IsCallReloc, CLI, Callee,
+                                  Chain);
 }
 
 SDValue MipsSETargetLowering::lowerLOAD(SDValue Op, SelectionDAG &DAG) const {
   LoadSDNode &Nd = *cast<LoadSDNode>(Op);
 
   if (Nd.getMemoryVT() != MVT::f64 || !NoDPLoadStore)
     return MipsTargetLowering::lowerLOAD(Op, DAG);
 

test/CodeGen/Mips/gpreg-lazy-binding.ll

 define internal fastcc void @internalFunc() nounwind noinline {
 entry:
   %0 = load i32* @g, align 4
   %inc = add nsw i32 %0, 1
   store i32 %inc, i32* @g, align 4
   ret void
 }
 
+define void @no_lazy(void (i32)* %pf) {
+
+; CHECK-LABEL:  no_lazy
+; CHECK-NOT:    gp_disp
+
+  tail call void %pf(i32 1)
+  ret void
+}

test/CodeGen/Mips/prevent-hoisting.ll

 ; RUN: llc -march=mipsel -O3 < %s | FileCheck %s
 
 
 ; MIPS direct branches implicitly define register $at. This test makes sure that
 ; code hoisting optimization (which moves identical instructions at the start of
 ; two basic blocks to the common predecessor block) takes this into account and
 ; doesn't move definition of $at to the predecessor block (which would make $at
 ; live-in at the start of successor block).
 
 
 ; CHECK-LABEL: readLumaCoeff8x8_CABAC
 
-; The check for "addiu" instruction is added so that we can match the correct "b" instruction.
+; The check for first "addiu" instruction is added so that we can match the correct "b" instruction.
 ; CHECK:           addiu ${{[0-9]+}}, $zero, -1
 ; CHECK:           b $[[BB0:BB[0-9_]+]]
+; CHECK-NEXT:      addiu ${{[0-9]+}}, $zero, 0
 
-; Check that sll instruction that writes to $1 starts basic block.
-; CHECK:       {{BB[0-9_#]+}}: 
+; Check that at the start of a fallthrough block there is a instruction that writes to $1.
+; CHECK-NEXT:  {{BB[0-9_#]+}}: 
+; CHECK-NEXT:      lw      $[[R1:[0-9]+]], %got(assignSE2partition)($[[R2:[0-9]+]])
 ; CHECK-NEXT:      sll $1, $[[R0:[0-9]+]], 4
 
-; Check that identical sll instruction starts another basic block.
+; Check that identical instructions are at the start of a target block.
 ; CHECK:       [[BB0]]:
+; CHECK-NEXT:      lw      $[[R1]], %got(assignSE2partition)($[[R2]])
 ; CHECK-NEXT:      sll $1, $[[R0]], 4
 
 
 %struct.img_par = type { i32, i32, i32, i32, i32*, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, [16 x [16 x i16]], [6 x [32 x i32]], [16 x [16 x i32]], [4 x [12 x [4 x [4 x i32]]]], [16 x i32], i8**, i32*, i32***, i32**, i32, i32, i32, i32, %struct.Slice*, %struct.macroblock*, i32, i32, i32, i32, i32, i32, %struct.DecRefPicMarking_s*, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, [3 x i32], i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32***, i32***, i32****, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, [3 x [2 x i32]], [3 x [2 x i32]], i32, i32, i32, i32, %struct.timeb, %struct.timeb, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32, i32 }
 %struct.Slice = type { i32, i32, i32, i32, i32, i32, i32, i32, i32, %struct.datapartition*, %struct.MotionInfoContexts*, %struct.TextureInfoContexts*, i32, i32*, i32*, i32*, i32, i32*, i32*, i32*, i32 (%struct.img_par*, %struct.inp_par*)*, i32, i32, i32, i32 }
 %struct.datapartition = type { %struct.Bitstream*, %struct.DecodingEnvironment, i32 (%struct.syntaxelement*, %struct.img_par*, %struct.datapartition*)* }
 %struct.Bitstream = type { i32, i32, i32, i32, i8*, i32 }
 %struct.DecodingEnvironment = type { i32, i32, i32, i32, i32, i8*, i32* }
 %struct.syntaxelement = type { i32, i32, i32, i32, i32, i32, i32, i32, void (i32, i32, i32*, i32*)*, void (%struct.syntaxelement*, %struct.img_par*, %struct.DecodingEnvironment*)* }