From a931a12e04b856421977c86d94789cd8b47d6ad3 Mon Sep 17 00:00:00 2001 From: Cameron Zwarich Date: Thu, 21 Feb 2013 22:58:42 +0000 Subject: [PATCH] Stop relying on physical register kill flags in isKilled() in the two-address pass. One of the callers of isKilled() can cope with overapproximation of kills and the other can't, so I added a flag to indicate this. In theory this could pessimize code slightly, but in practice most physical register uses are kills, and most important kills of physical registers are the only uses of that register prior to register allocation, so we can recognize them as kills even without kill flags. This is relevant because LiveIntervals gets rid of all kill flags. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175821 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/CodeGen/TwoAddressInstructionPass.cpp | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-) diff --git a/lib/CodeGen/TwoAddressInstructionPass.cpp b/lib/CodeGen/TwoAddressInstructionPass.cpp index e0dba3f2916..e31264207c3 100644 --- a/lib/CodeGen/TwoAddressInstructionPass.cpp +++ b/lib/CodeGen/TwoAddressInstructionPass.cpp @@ -372,12 +372,19 @@ static bool isPlainlyKilled(MachineInstr *MI, unsigned Reg, /// normal heuristics commute the (two-address) add, which lets /// coalescing eliminate the extra copy. /// +/// If allowFalsePositives is true then likely kills are treated as kills even +/// if it can't be proven that they are kills. static bool isKilled(MachineInstr &MI, unsigned Reg, const MachineRegisterInfo *MRI, const TargetInstrInfo *TII, - LiveIntervals *LIS) { + LiveIntervals *LIS, + bool allowFalsePositives) { MachineInstr *DefMI = &MI; for (;;) { + // All uses of physical registers are likely to be kills. + if (TargetRegisterInfo::isPhysicalRegister(Reg) && + (allowFalsePositives || MRI->hasOneUse(Reg))) + return true; if (!isPlainlyKilled(DefMI, Reg, LIS)) return false; if (TargetRegisterInfo::isPhysicalRegister(Reg)) @@ -1028,7 +1035,7 @@ tryInstructionTransform(MachineBasicBlock::iterator &mi, assert(TargetRegisterInfo::isVirtualRegister(regB) && "cannot make instruction into two-address form"); - bool regBKilled = isKilled(MI, regB, MRI, TII, LIS); + bool regBKilled = isKilled(MI, regB, MRI, TII, LIS, true); if (TargetRegisterInfo::isVirtualRegister(regA)) scanUses(regA); @@ -1048,7 +1055,7 @@ tryInstructionTransform(MachineBasicBlock::iterator &mi, if (regCIdx != ~0U) { regC = MI.getOperand(regCIdx).getReg(); - if (!regBKilled && isKilled(MI, regC, MRI, TII, LIS)) + if (!regBKilled && isKilled(MI, regC, MRI, TII, LIS, false)) // If C dies but B does not, swap the B and C operands. // This makes the live ranges of A and C joinable. TryCommute = true; -- 2.34.1