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,
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:
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,
%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
+}