Revert r157755.

The commit is intended to fix rdar://11540023.
It is implemented as part of peephole optimization. We can actually implement
this in the SelectionDAG lowering phase.

llvm-svn: 158122

llvm/include/llvm/Target/TargetInstrInfo.h

@@ -640,14 +640,6 @@ public:
     return false;
   }
 
-  /// OptimizeSubInstr - See if the SUB instruction can be converted into
-  /// something more efficient E.g., on X86, we can replace SUB with CMP
-  /// if the actual result of SUB is not used.
-  virtual bool OptimizeSubInstr(MachineInstr *SubInstr,
-                                const MachineRegisterInfo *MRI) const {
-    return false;
-  }
-
   /// FoldImmediate - 'Reg' is known to be defined by a move immediate
   /// instruction, try to fold the immediate into the use instruction.
   virtual bool FoldImmediate(MachineInstr *UseMI, MachineInstr *DefMI,

llvm/lib/CodeGen/PeepholeOptimizer.cpp

@@ -472,7 +472,6 @@ bool PeepholeOptimizer::runOnMachineFunction(MachineFunction &MF) {
         if (SeenMoveImm)
           Changed |= foldImmediate(MI, MBB, ImmDefRegs, ImmDefMIs);
       }
-      Changed |= TII->OptimizeSubInstr(MI, MRI);
 
       First = false;
       PMII = MII;

llvm/lib/Target/X86/X86InstrInfo.cpp

@@ -2793,44 +2793,6 @@ void X86InstrInfo::loadRegFromAddr(MachineFunction &MF, unsigned DestReg,
   NewMIs.push_back(MIB);
 }
 
-bool X86InstrInfo::
-OptimizeSubInstr(MachineInstr *SubInstr, const MachineRegisterInfo *MRI) const {
-  // If destination is a memory operand, do not perform this optimization.
-  if ((SubInstr->getOpcode() != X86::SUB64rr) &&
-      (SubInstr->getOpcode() != X86::SUB32rr) &&
-      (SubInstr->getOpcode() != X86::SUB16rr) &&
-      (SubInstr->getOpcode() != X86::SUB8rr) &&
-      (SubInstr->getOpcode() != X86::SUB64ri32) &&
-      (SubInstr->getOpcode() != X86::SUB64ri8) &&
-      (SubInstr->getOpcode() != X86::SUB32ri) &&
-      (SubInstr->getOpcode() != X86::SUB32ri8) &&
-      (SubInstr->getOpcode() != X86::SUB16ri) &&
-      (SubInstr->getOpcode() != X86::SUB16ri8) &&
-      (SubInstr->getOpcode() != X86::SUB8ri))
-    return false;
-  unsigned DestReg = SubInstr->getOperand(0).getReg();
-  if (MRI->use_begin(DestReg) != MRI->use_end())
-    return false;
-
-  // There is no use of the destination register, we can replace SUB with CMP.
-  switch (SubInstr->getOpcode()) {
-    default: break;
-    case X86::SUB64rr:   SubInstr->setDesc(get(X86::CMP64rr));   break;
-    case X86::SUB32rr:   SubInstr->setDesc(get(X86::CMP32rr));   break;
-    case X86::SUB16rr:   SubInstr->setDesc(get(X86::CMP16rr));   break;
-    case X86::SUB8rr:    SubInstr->setDesc(get(X86::CMP8rr));    break;
-    case X86::SUB64ri32: SubInstr->setDesc(get(X86::CMP64ri32)); break;
-    case X86::SUB64ri8:  SubInstr->setDesc(get(X86::CMP64ri8));  break;
-    case X86::SUB32ri:   SubInstr->setDesc(get(X86::CMP32ri));   break;
-    case X86::SUB32ri8:  SubInstr->setDesc(get(X86::CMP32ri8));  break;
-    case X86::SUB16ri:   SubInstr->setDesc(get(X86::CMP16ri));   break;
-    case X86::SUB16ri8:  SubInstr->setDesc(get(X86::CMP16ri8));  break;
-    case X86::SUB8ri:    SubInstr->setDesc(get(X86::CMP8ri));    break;
-  }
-  SubInstr->RemoveOperand(0);
-  return true;
-}
-
 /// Expand2AddrUndef - Expand a single-def pseudo instruction to a two-addr
 /// instruction with two undef reads of the register being defined.  This is
 /// used for mapping:

llvm/lib/Target/X86/X86InstrInfo.h

@@ -364,9 +364,6 @@ public:
                              const MachineInstr *DefMI, unsigned DefIdx,
                              const MachineInstr *UseMI, unsigned UseIdx) const;
 
-  virtual bool OptimizeSubInstr(MachineInstr *SubInstr,
-                                const MachineRegisterInfo *MRI) const;
-
 private:
   MachineInstr * convertToThreeAddressWithLEA(unsigned MIOpc,
                                               MachineFunction::iterator &MFI,

llvm/test/CodeGen/X86/jump_sign.ll

@@ -83,14 +83,3 @@ entry:
   %cond = select i1 %cmp, i32 %sub, i32 0
   ret i32 %cond
 }
-; rdar://11540023
-define i64 @n(i64 %x, i64 %y) nounwind {
-entry:
-; CHECK: n:
-; CHECK-NOT: sub
-; CHECK: cmp
-  %sub = sub nsw i64 %x, %y
-  %cmp = icmp slt i64 %sub, 0
-  %y.x = select i1 %cmp, i64 %y, i64 %x
-  ret i64 %y.x
-}