diff options
| -rw-r--r-- | llvm/lib/Target/X86/X86InstrInfo.cpp | 39 |
1 files changed, 32 insertions, 7 deletions
diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp index 0d29aa9db6a..e8a39d11040 100644 --- a/llvm/lib/Target/X86/X86InstrInfo.cpp +++ b/llvm/lib/Target/X86/X86InstrInfo.cpp @@ -853,7 +853,7 @@ X86InstrInfo::isReallyTriviallyReMaterializable(const MachineInstr *MI, /// isSafeToClobberEFLAGS - Return true if it's safe insert an instruction that /// would clobber the EFLAGS condition register. Note the result may be /// conservative. If it cannot definitely determine the safety after visiting -/// two instructions it assumes it's not safe. +/// a few instructions in each direction it assumes it's not safe. static bool isSafeToClobberEFLAGS(MachineBasicBlock &MBB, MachineBasicBlock::iterator I) { // It's always safe to clobber EFLAGS at the end of a block. @@ -861,11 +861,13 @@ static bool isSafeToClobberEFLAGS(MachineBasicBlock &MBB, return true; // For compile time consideration, if we are not able to determine the - // safety after visiting 2 instructions, we will assume it's not safe. - for (unsigned i = 0; i < 2; ++i) { + // safety after visiting 4 instructions in each direction, we will assume + // it's not safe. + MachineBasicBlock::iterator Iter = I; + for (unsigned i = 0; i < 4; ++i) { bool SeenDef = false; - for (unsigned j = 0, e = I->getNumOperands(); j != e; ++j) { - MachineOperand &MO = I->getOperand(j); + for (unsigned j = 0, e = Iter->getNumOperands(); j != e; ++j) { + MachineOperand &MO = Iter->getOperand(j); if (!MO.isReg()) continue; if (MO.getReg() == X86::EFLAGS) { @@ -878,10 +880,33 @@ static bool isSafeToClobberEFLAGS(MachineBasicBlock &MBB, if (SeenDef) // This instruction defines EFLAGS, no need to look any further. return true; - ++I; + ++Iter; // If we make it to the end of the block, it's safe to clobber EFLAGS. - if (I == MBB.end()) + if (Iter == MBB.end()) + return true; + } + + Iter = I; + for (unsigned i = 0; i < 4; ++i) { + // If we make it to the beginning of the block, it's safe to clobber + // EFLAGS iff EFLAGS is not live-in. + if (Iter == MBB.begin()) + return !MBB.isLiveIn(X86::EFLAGS); + + --Iter; + bool SawKill = false; + for (unsigned j = 0, e = Iter->getNumOperands(); j != e; ++j) { + MachineOperand &MO = Iter->getOperand(j); + if (MO.isReg() && MO.getReg() == X86::EFLAGS) { + if (MO.isDef()) return MO.isDead(); + if (MO.isKill()) SawKill = true; + } + } + + if (SawKill) + // This instruction kills EFLAGS and doesn't redefine it, so + // there's no need to look further. return true; } |
