[PowerPC][NFC] Add a function to determine if a call needs to be NOTOC.

[stefanp]

Summary

Add the isNoTOCCallInstr function to PPCInstrInfo to determine if a call opcode
does not need a TOC restore after the call. All call opcodes should be listed in
this function. A default unreachable in this function should force future call
opcodes to also be added.

This is a follow up patch to D122012

[shchenz]

llvm/lib/Target/PowerPC/PPCInstrInfo.h

299

I am in favor of Jinsong's comment in https://reviews.llvm.org/D122012#3392673. Could we use a flag in the td file (with a default true/false value) instead of listing all call instructions in the cpp file?

[jsji]

LGTM. Thanks.

llvm/lib/Target/PowerPC/PPCInstrInfo.h

299

Thanks Zheng, we had some offline discussion, and I agreed that this can be a tradeoff between cost and benefits.
So I am OK with this.

[shchenz]

llvm/lib/Target/PowerPC/PPCInstrInfo.h

299

Oh, I don't realize this. Could you please explain why we choose the cpp function instead of a td flag? To me, when we add a new call instruction in td file in future, it should be easier to aware that there is a flag to tell whether this call instruction needs a nop or not. Thanks

[jsji]

llvm/lib/Target/PowerPC/PPCInstrInfo.h

299

We will need some big in TSFlags to check the td flag, and currently this only affects 3 opcode, and it is highly unlikely we will be adding more NOTOC call instructions.
So this explicitly listed switch table is mostly as a tradeoff of saving bits in TSFlags

[shchenz]

LGTM with one nit.

llvm/lib/Target/PowerPC/PPCInstrInfo.h

299

OK, thanks for explanation.

314

nit: maybe we can also guard these false cases under #ifndef NDEBUG?

[stefanp]

Rebased patch to top of trunk.
Added the additional #ifndef NDEBUG.

llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCCodeEmitter.cpp

 unsigned PPCMCCodeEmitter::
 getDirectBrEncoding(const MCInst &MI, unsigned OpNo,
                     SmallVectorImpl<MCFixup> &Fixups,
                     const MCSubtargetInfo &STI) const {
   const MCOperand &MO = MI.getOperand(OpNo);
 
   if (MO.isReg() || MO.isImm())
     return getMachineOpValue(MI, MO, Fixups, STI);
+
+  const PPCInstrInfo *InstrInfo = static_cast<const PPCInstrInfo *>(&MCII);
+  unsigned Opcode = MI.getOpcode();
   // Add a fixup for the branch target.
   Fixups.push_back(MCFixup::create(0, MO.getExpr(),
-                                   ((MI.getOpcode() == PPC::BL8_NOTOC ||
-                                     MI.getOpcode() == PPC::BL8_NOTOC_TLS ||
-                                     MI.getOpcode() == PPC::BL8_NOTOC_RM)
+                                   (InstrInfo->isNoTOCCallInstr(Opcode)
                                         ? (MCFixupKind)PPC::fixup_ppc_br24_notoc
                                         : (MCFixupKind)PPC::fixup_ppc_br24)));
   return 0;
 }
 
 unsigned PPCMCCodeEmitter::getCondBrEncoding(const MCInst &MI, unsigned OpNo,
                                      SmallVectorImpl<MCFixup> &Fixups,
                                      const MCSubtargetInfo &STI) const {

llvm/lib/Target/PowerPC/PPCInstrInfo.h

public:
 
   bool isXFormMemOp(unsigned Opcode) const {
     return get(Opcode).TSFlags & PPCII::XFormMemOp;
   }
   bool isPrefixed(unsigned Opcode) const {
     return get(Opcode).TSFlags & PPCII::Prefixed;
   }
 
+  /// Check if Opcode corresponds to a call instruction that should be marked
+  /// with the NOTOC relocation.
+  bool isNoTOCCallInstr(unsigned Opcode) const {
+    if (!get(Opcode).isCall())
+      return false;
+
+    switch (Opcode) {
+    default:
+#ifndef NDEBUG
+      llvm_unreachable("Unknown call opcode");
+#endif
+      return false;
+    case PPC::BL8_NOTOC:
+    case PPC::BL8_NOTOC_TLS:
+    case PPC::BL8_NOTOC_RM:
+      return true;
+#ifndef NDEBUG
+    case PPC::BL8:
+    case PPC::BL:
+    case PPC::BL8_TLS:
+    case PPC::BL_TLS:
+    case PPC::BLA8:
+    case PPC::BLA:
+    case PPC::BCCL:
+    case PPC::BCCLA:
+    case PPC::BCL:
+    case PPC::BCLn:
+    case PPC::BL8_NOP:
+    case PPC::BL_NOP:
+    case PPC::BL8_NOP_TLS:
+    case PPC::BLA8_NOP:
+    case PPC::BCTRL8:
+    case PPC::BCTRL:
+    case PPC::BCCCTRL8:
+    case PPC::BCCCTRL:
+    case PPC::BCCTRL8:
+    case PPC::BCCTRL:
+    case PPC::BCCTRL8n:
+    case PPC::BCCTRLn:
+    case PPC::BL8_RM:
+    case PPC::BLA8_RM:
+    case PPC::BL8_NOP_RM:
+    case PPC::BLA8_NOP_RM:
+    case PPC::BCTRL8_RM:
+    case PPC::BCTRL8_LDinto_toc:
+    case PPC::BCTRL8_LDinto_toc_RM:
+    case PPC::BL8_TLS_:
+    case PPC::TCRETURNdi8:
+    case PPC::TCRETURNai8:
+    case PPC::TCRETURNri8:
+    case PPC::TAILBCTR8:
+    case PPC::TAILB8:
+    case PPC::TAILBA8:
+    case PPC::BCLalways:
+    case PPC::BLRL:
+    case PPC::BCCLRL:
+    case PPC::BCLRL:
+    case PPC::BCLRLn:
+    case PPC::BDZL:
+    case PPC::BDNZL:
+    case PPC::BDZLA:
+    case PPC::BDNZLA:
+    case PPC::BDZLp:
+    case PPC::BDNZLp:
+    case PPC::BDZLAp:
+    case PPC::BDNZLAp:
+    case PPC::BDZLm:
+    case PPC::BDNZLm:
+    case PPC::BDZLAm:
+    case PPC::BDNZLAm:
+    case PPC::BDZLRL:
+    case PPC::BDNZLRL:
+    case PPC::BDZLRLp:
+    case PPC::BDNZLRLp:
+    case PPC::BDZLRLm:
+    case PPC::BDNZLRLm:
+    case PPC::BL_RM:
+    case PPC::BLA_RM:
+    case PPC::BL_NOP_RM:
+    case PPC::BCTRL_RM:
+    case PPC::TCRETURNdi:
+    case PPC::TCRETURNai:
+    case PPC::TCRETURNri:
+    case PPC::BCTRL_LWZinto_toc:
+    case PPC::BCTRL_LWZinto_toc_RM:
+    case PPC::TAILBCTR:
+    case PPC::TAILB:
+    case PPC::TAILBA:
+      return false;
+#endif
+    }
+  }
+
   static bool isSameClassPhysRegCopy(unsigned Opcode) {
     unsigned CopyOpcodes[] = {PPC::OR,        PPC::OR8,   PPC::FMR,
                               PPC::VOR,       PPC::XXLOR, PPC::XXLORf,
                               PPC::XSCPSGNDP, PPC::MCRF,  PPC::CROR,
                               PPC::EVOR,      -1U};
     for (int i = 0; CopyOpcodes[i] != -1U; i++)
       if (Opcode == CopyOpcodes[i])
         return true;