diff options
Diffstat (limited to 'llvm/lib/Target/X86/X86InstrInfo.cpp')
| -rw-r--r-- | llvm/lib/Target/X86/X86InstrInfo.cpp | 16 |
1 files changed, 13 insertions, 3 deletions
diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp index 12da3a9319e..e9d36f8ce2f 100644 --- a/llvm/lib/Target/X86/X86InstrInfo.cpp +++ b/llvm/lib/Target/X86/X86InstrInfo.cpp @@ -4412,9 +4412,19 @@ void X86InstrInfo::copyPhysReg(MachineBasicBlock &MBB, int Pop = is64 ? X86::POP64r : X86::POP32r; int AX = is64 ? X86::RAX : X86::EAX; - bool AXDead = (Reg == AX) || - (MachineBasicBlock::LQR_Dead == - MBB.computeRegisterLiveness(&getRegisterInfo(), AX, MI)); + bool AXDead = (Reg == AX); + // FIXME: The above could figure out that AX is dead in more cases with: + // || (MachineBasicBlock::LQR_Dead == + // MBB.computeRegisterLiveness(&getRegisterInfo(), AX, MI)); + // + // Unfortunately this is slightly broken, see PR24535 and the likely + // related PR25033 PR24991 PR24992 PR25201. These issues seem to + // showcase sub-register / super-register confusion: a previous kill + // of AH but no kill of AL leads computeRegisterLiveness to + // erroneously conclude that AX is dead. + // + // Once fixed, also update cmpxchg-clobber-flags.ll and + // peephole-na-phys-copy-folding.ll. if (!AXDead) BuildMI(MBB, MI, DL, get(Push)).addReg(AX, getKillRegState(true)); |
