diff options
Diffstat (limited to 'llvm/lib')
-rw-r--r-- | llvm/lib/Target/X86/X86InstrInfo.cpp | 30 |
1 files changed, 25 insertions, 5 deletions
diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp index 7899985badc..f493438c29c 100644 --- a/llvm/lib/Target/X86/X86InstrInfo.cpp +++ b/llvm/lib/Target/X86/X86InstrInfo.cpp @@ -3107,22 +3107,28 @@ optimizeCompareInstr(MachineInstr *CmpInstr, unsigned SrcReg, unsigned SrcReg2, if (!Sub) return false; + bool IsSwapped = (SrcReg2 != 0 && Sub->getOperand(1).getReg() == SrcReg2 && + Sub->getOperand(2).getReg() == SrcReg); + // Scan forward from the instruction after CmpInstr for uses of EFLAGS. + // It is safe to remove CmpInstr if EFLAGS is redefined or killed. + // If we are done with the basic block, we need to check whether EFLAGS is + // live-out. + bool IsSafe = false; SmallVector<std::pair<MachineInstr*, unsigned /*NewOpc*/>, 4> OpsToUpdate; MachineBasicBlock::iterator E = CmpInstr->getParent()->end(); for (++I; I != E; ++I) { const MachineInstr &Instr = *I; - if (Instr.modifiesRegister(X86::EFLAGS, TRI)) + if (Instr.modifiesRegister(X86::EFLAGS, TRI)) { // It is safe to remove CmpInstr if EFLAGS is updated again. + IsSafe = true; break; - + } if (!Instr.readsRegister(X86::EFLAGS, TRI)) continue; // EFLAGS is used by this instruction. - if (SrcReg2 != 0 && Sub->getOperand(1).getReg() == SrcReg2 && - Sub->getOperand(2).getReg() == SrcReg) { - + if (IsSwapped) { // If we have SUB(r1, r2) and CMP(r2, r1), the condition code needs // to be changed from r2 > r1 to r1 < r2, from r2 < r1 to r1 > r2, etc. unsigned NewOpc = getSwappedConditionForSET(Instr.getOpcode()); @@ -3135,6 +3141,20 @@ optimizeCompareInstr(MachineInstr *CmpInstr, unsigned SrcReg, unsigned SrcReg2, // instructions will be modified. OpsToUpdate.push_back(std::make_pair(&*I, NewOpc)); } + if (Instr.killsRegister(X86::EFLAGS, TRI)) { + IsSafe = true; + break; + } + } + + // If EFLAGS is not killed nor re-defined, we should check whether it is + // live-out. If it is live-out, do not optimize. + if (IsSwapped && !IsSafe) { + MachineBasicBlock *MBB = CmpInstr->getParent(); + for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(), + SE = MBB->succ_end(); SI != SE; ++SI) + if ((*SI)->isLiveIn(X86::EFLAGS)) + return false; } // Make sure Sub instruction defines EFLAGS. |