[X86] Disable conditional tail calls (PR31257)

They are currently modelled incorrectly (as calls, which clobber
registers, confusing e.g. Machine Copy Propagation).

Reverting until we figure out the proper solution.

llvm-svn: 294348

6 files changed, 2 insertions, 182 deletions

diff --git a/llvm/lib/CodeGen/BranchFolding.cpp b/llvm/lib/CodeGen/BranchFolding.cpp
index c632eb7ab7d..b196bf98d27 100644
--- a/llvm/lib/CodeGen/BranchFolding.cpp
+++ b/llvm/lib/CodeGen/BranchFolding.cpp
@@ -49,7 +49,6 @@ STATISTIC(NumDeadBlocks, "Number of dead blocks removed");
 STATISTIC(NumBranchOpts, "Number of branches optimized");
 STATISTIC(NumTailMerge , "Number of block tails merged");
 STATISTIC(NumHoist     , "Number of times common instructions are hoisted");
-STATISTIC(NumTailCalls,  "Number of tail calls optimized");
 
 static cl::opt<cl::boolOrDefault> FlagEnableTailMerge("enable-tail-merge",
                               cl::init(cl::BOU_UNSET), cl::Hidden);
@@ -1394,42 +1393,6 @@ ReoptimizeBlock:
     }
   }
 
-  if (!IsEmptyBlock(MBB) && MBB->pred_size() == 1 &&
-      MF.getFunction()->optForSize()) {
-    // Changing "Jcc foo; foo: jmp bar;" into "Jcc bar;" might change the branch
-    // direction, thereby defeating careful block placement and regressing
-    // performance. Therefore, only consider this for optsize functions.
-    MachineInstr &TailCall = *MBB->getFirstNonDebugInstr();
-    if (TII->isUnconditionalTailCall(TailCall)) {
-      MachineBasicBlock *Pred = *MBB->pred_begin();
-      MachineBasicBlock *PredTBB = nullptr, *PredFBB = nullptr;
-      SmallVector<MachineOperand, 4> PredCond;
-      bool PredAnalyzable =
-          !TII->analyzeBranch(*Pred, PredTBB, PredFBB, PredCond, true);
-
-      if (PredAnalyzable && !PredCond.empty() && PredTBB == MBB) {
-        // The predecessor has a conditional branch to this block which consists
-        // of only a tail call. Try to fold the tail call into the conditional
-        // branch.
-        if (TII->canMakeTailCallConditional(PredCond, TailCall)) {
-          // TODO: It would be nice if analyzeBranch() could provide a pointer
-          // to the branch insturction so replaceBranchWithTailCall() doesn't
-          // have to search for it.
-          TII->replaceBranchWithTailCall(*Pred, PredCond, TailCall);
-          ++NumTailCalls;
-          Pred->removeSuccessor(MBB);
-          MadeChange = true;
-          return MadeChange;
-        }
-      }
-      // If the predecessor is falling through to this block, we could reverse
-      // the branch condition and fold the tail call into that. However, after
-      // that we might have to re-arrange the CFG to fall through to the other
-      // block and there is a high risk of regressing code size rather than
-      // improving it.
-    }
-  }
-
   // Analyze the branch in the current block.
   MachineBasicBlock *CurTBB = nullptr, *CurFBB = nullptr;
   SmallVector<MachineOperand, 4> CurCond;
diff --git a/llvm/lib/Target/X86/X86ExpandPseudo.cpp b/llvm/lib/Target/X86/X86ExpandPseudo.cpp
index c4bc29e963e..6a2cf1d5314 100644
--- a/llvm/lib/Target/X86/X86ExpandPseudo.cpp
+++ b/llvm/lib/Target/X86/X86ExpandPseudo.cpp
@@ -77,11 +77,9 @@ bool X86ExpandPseudo::ExpandMI(MachineBasicBlock &MBB,
   default:
     return false;
   case X86::TCRETURNdi:
-  case X86::TCRETURNdicc:
   case X86::TCRETURNri:
   case X86::TCRETURNmi:
   case X86::TCRETURNdi64:
-  case X86::TCRETURNdi64cc:
   case X86::TCRETURNri64:
   case X86::TCRETURNmi64: {
     bool isMem = Opcode == X86::TCRETURNmi || Opcode == X86::TCRETURNmi64;
@@ -99,10 +97,6 @@ bool X86ExpandPseudo::ExpandMI(MachineBasicBlock &MBB,
     Offset = StackAdj - MaxTCDelta;
     assert(Offset >= 0 && "Offset should never be negative");
 
-    if (Opcode == X86::TCRETURNdicc || Opcode == X86::TCRETURNdi64cc) {
-      assert(Offset == 0 && "Conditional tail call cannot adjust the stack.");
-    }
-
     if (Offset) {
       // Check for possible merge with preceding ADD instruction.
       Offset += X86FL->mergeSPUpdates(MBB, MBBI, true);
@@ -111,21 +105,12 @@ bool X86ExpandPseudo::ExpandMI(MachineBasicBlock &MBB,
 
     // Jump to label or value in register.
     bool IsWin64 = STI->isTargetWin64();
-    if (Opcode == X86::TCRETURNdi || Opcode == X86::TCRETURNdicc ||
-        Opcode == X86::TCRETURNdi64 || Opcode == X86::TCRETURNdi64cc) {
+    if (Opcode == X86::TCRETURNdi || Opcode == X86::TCRETURNdi64) {
       unsigned Op;
       switch (Opcode) {
       case X86::TCRETURNdi:
         Op = X86::TAILJMPd;
         break;
-      case X86::TCRETURNdicc:
-        Op = X86::TAILJMPd_CC;
-        break;
-      case X86::TCRETURNdi64cc:
-        assert(!IsWin64 && "Conditional tail calls confuse the Win64 unwinder.");
-        // TODO: We could do it for Win64 "leaf" functions though; PR30337.
-        Op = X86::TAILJMPd64_CC;
-        break;
       default:
         // Note: Win64 uses REX prefixes indirect jumps out of functions, but
         // not direct ones.
@@ -141,10 +126,6 @@ bool X86ExpandPseudo::ExpandMI(MachineBasicBlock &MBB,
         MIB.addExternalSymbol(JumpTarget.getSymbolName(),
                               JumpTarget.getTargetFlags());
       }
-      if (Op == X86::TAILJMPd_CC || Op == X86::TAILJMPd64_CC) {
-        MIB.addImm(MBBI->getOperand(2).getImm());
-      }
-
     } else if (Opcode == X86::TCRETURNmi || Opcode == X86::TCRETURNmi64) {
       unsigned Op = (Opcode == X86::TCRETURNmi)
                         ? X86::TAILJMPm
diff --git a/llvm/lib/Target/X86/X86InstrControl.td b/llvm/lib/Target/X86/X86InstrControl.td
index 4ea223e82be..2f260c48df4 100644
--- a/llvm/lib/Target/X86/X86InstrControl.td
+++ b/llvm/lib/Target/X86/X86InstrControl.td
@@ -264,21 +264,6 @@ let isCall = 1, isTerminator = 1, isReturn = 1, isBarrier = 1,
                    "jmp{l}\t{*}$dst", [], IIC_JMP_MEM>;
 }
 
-// Conditional tail calls are similar to the above, but they are branches
-// rather than barriers, and they use EFLAGS.
-let isCall = 1, isTerminator = 1, isReturn = 1, isBranch = 1,
-    isCodeGenOnly = 1, SchedRW = [WriteJumpLd] in
-  let Uses = [ESP, EFLAGS] in {
-  def TCRETURNdicc : PseudoI<(outs),
-                     (ins i32imm_pcrel:$dst, i32imm:$offset, i32imm:$cond), []>;
-
-  // This gets substituted to a conditional jump instruction in MC lowering.
-  def TAILJMPd_CC : Ii32PCRel<0x80, RawFrm, (outs),
-                           (ins i32imm_pcrel:$dst, i32imm:$cond),
-                           "",
-                           [], IIC_JMP_REL>;
-}
-
 
 //===----------------------------------------------------------------------===//
 //  Call Instructions...
@@ -340,19 +325,3 @@ let isCall = 1, isTerminator = 1, isReturn = 1, isBarrier = 1,
                            "rex64 jmp{q}\t{*}$dst", [], IIC_JMP_MEM>;
   }
 }
-
-// Conditional tail calls are similar to the above, but they are branches
-// rather than barriers, and they use EFLAGS.
-let isCall = 1, isTerminator = 1, isReturn = 1, isBranch = 1,
-    isCodeGenOnly = 1, SchedRW = [WriteJumpLd] in
-  let Uses = [RSP, EFLAGS] in {
-  def TCRETURNdi64cc : PseudoI<(outs),
-                           (ins i64i32imm_pcrel:$dst, i32imm:$offset,
-                            i32imm:$cond), []>;
-
-  // This gets substituted to a conditional jump instruction in MC lowering.
-  def TAILJMPd64_CC : Ii32PCRel<0x80, RawFrm, (outs),
-                           (ins i64i32imm_pcrel:$dst, i32imm:$cond),
-                           "",
-                           [], IIC_JMP_REL>;
-}
diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index 87f4a9946f2..a9b29818505 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -5577,85 +5577,6 @@ bool X86InstrInfo::isUnpredicatedTerminator(const MachineInstr &MI) const {
   return !isPredicated(MI);
 }
 
-bool X86InstrInfo::isUnconditionalTailCall(const MachineInstr &MI) const {
-  switch (MI.getOpcode()) {
-  case X86::TCRETURNdi:
-  case X86::TCRETURNri:
-  case X86::TCRETURNmi:
-  case X86::TCRETURNdi64:
-  case X86::TCRETURNri64:
-  case X86::TCRETURNmi64:
-    return true;
-  default:
-    return false;
-  }
-}
-
-bool X86InstrInfo::canMakeTailCallConditional(
-    SmallVectorImpl<MachineOperand> &BranchCond,
-    const MachineInstr &TailCall) const {
-  if (TailCall.getOpcode() != X86::TCRETURNdi &&
-      TailCall.getOpcode() != X86::TCRETURNdi64) {
-    // Only direct calls can be done with a conditional branch.
-    return false;
-  }
-
-  if (Subtarget.isTargetWin64()) {
-    // Conditional tail calls confuse the Win64 unwinder.
-    // TODO: Allow them for "leaf" functions; PR30337.
-    return false;
-  }
-
-  assert(BranchCond.size() == 1);
-  if (BranchCond[0].getImm() > X86::LAST_VALID_COND) {
-    // Can't make a conditional tail call with this condition.
-    return false;
-  }
-
-  const X86MachineFunctionInfo *X86FI =
-      TailCall.getParent()->getParent()->getInfo<X86MachineFunctionInfo>();
-  if (X86FI->getTCReturnAddrDelta() != 0 ||
-      TailCall.getOperand(1).getImm() != 0) {
-    // A conditional tail call cannot do any stack adjustment.
-    return false;
-  }
-
-  return true;
-}
-
-void X86InstrInfo::replaceBranchWithTailCall(
-    MachineBasicBlock &MBB, SmallVectorImpl<MachineOperand> &BranchCond,
-    const MachineInstr &TailCall) const {
-  assert(canMakeTailCallConditional(BranchCond, TailCall));
-
-  MachineBasicBlock::iterator I = MBB.end();
-  while (I != MBB.begin()) {
-    --I;
-    if (I->isDebugValue())
-      continue;
-    if (!I->isBranch())
-      assert(0 && "Can't find the branch to replace!");
-
-    X86::CondCode CC = getCondFromBranchOpc(I->getOpcode());
-    assert(BranchCond.size() == 1);
-    if (CC != BranchCond[0].getImm())
-      continue;
-
-    break;
-  }
-
-  unsigned Opc = TailCall.getOpcode() == X86::TCRETURNdi ? X86::TCRETURNdicc
-                                                         : X86::TCRETURNdi64cc;
-
-  auto MIB = BuildMI(MBB, I, MBB.findDebugLoc(I), get(Opc));
-  MIB->addOperand(TailCall.getOperand(0)); // Destination.
-  MIB.addImm(0); // Stack offset (not used).
-  MIB->addOperand(BranchCond[0]); // Condition.
-  MIB.copyImplicitOps(TailCall); // Regmask and (imp-used) parameters.
-
-  I->eraseFromParent();
-}
-
 // Given a MBB and its TBB, find the FBB which was a fallthrough MBB (it may
 // not be a fallthrough MBB now due to layout changes). Return nullptr if the
 // fallthrough MBB cannot be identified.
diff --git a/llvm/lib/Target/X86/X86InstrInfo.h b/llvm/lib/Target/X86/X86InstrInfo.h
index c2644a35e48..0d4bc5d0fb6 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.h
+++ b/llvm/lib/Target/X86/X86InstrInfo.h
@@ -316,13 +316,6 @@ public:
 
   // Branch analysis.
   bool isUnpredicatedTerminator(const MachineInstr &MI) const override;
-  bool isUnconditionalTailCall(const MachineInstr &MI) const override;
-  bool canMakeTailCallConditional(SmallVectorImpl<MachineOperand> &Cond,
-                                  const MachineInstr &TailCall) const override;
-  void replaceBranchWithTailCall(MachineBasicBlock &MBB,
-                                 SmallVectorImpl<MachineOperand> &Cond,
-                                 const MachineInstr &TailCall) const override;
-
   bool analyzeBranch(MachineBasicBlock &MBB, MachineBasicBlock *&TBB,
                      MachineBasicBlock *&FBB,
                      SmallVectorImpl<MachineOperand> &Cond,
diff --git a/llvm/lib/Target/X86/X86MCInstLower.cpp b/llvm/lib/Target/X86/X86MCInstLower.cpp
index 65949531126..0887643ed5a 100644
--- a/llvm/lib/Target/X86/X86MCInstLower.cpp
+++ b/llvm/lib/Target/X86/X86MCInstLower.cpp
@@ -499,16 +499,11 @@ ReSimplify:
     break;
   }
 
-  // TAILJMPd, TAILJMPd64, TailJMPd_cc - Lower to the correct jump instruction.
+  // TAILJMPd, TAILJMPd64 - Lower to the correct jump instruction.
   { unsigned Opcode;
   case X86::TAILJMPr:   Opcode = X86::JMP32r; goto SetTailJmpOpcode;
   case X86::TAILJMPd:
   case X86::TAILJMPd64: Opcode = X86::JMP_1;  goto SetTailJmpOpcode;
-  case X86::TAILJMPd_CC:
-  case X86::TAILJMPd64_CC:
-    Opcode = X86::GetCondBranchFromCond(
-        static_cast<X86::CondCode>(MI->getOperand(1).getImm()));
-    goto SetTailJmpOpcode;
 
   SetTailJmpOpcode:
     MCOperand Saved = OutMI.getOperand(0);
@@ -1299,11 +1294,9 @@ void X86AsmPrinter::EmitInstruction(const MachineInstr *MI) {
   case X86::TAILJMPr:
   case X86::TAILJMPm:
   case X86::TAILJMPd:
-  case X86::TAILJMPd_CC:
   case X86::TAILJMPr64:
   case X86::TAILJMPm64:
   case X86::TAILJMPd64:
-  case X86::TAILJMPd64_CC:
   case X86::TAILJMPr64_REX:
   case X86::TAILJMPm64_REX:
     // Lower these as normal, but add some comments.