[SystemZ] Use LOAD AND TEST to eliminate comparisons against zero
llvm-svn: 187720
diff --git a/llvm/lib/Target/SystemZ/SystemZElimCompare.cpp b/llvm/lib/Target/SystemZ/SystemZElimCompare.cpp
index 9b0bdd8..bcdc5b7 100644
--- a/llvm/lib/Target/SystemZ/SystemZElimCompare.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZElimCompare.cpp
@@ -46,6 +46,7 @@
bool runOnMachineFunction(MachineFunction &F);
private:
+ bool convertToLoadAndTest(MachineInstr *MI);
bool adjustCCMasksForInstr(MachineInstr *MI, MachineInstr *Compare,
SmallVectorImpl<MachineInstr *> &CCUsers);
bool optimizeCompareZero(MachineInstr *Compare,
@@ -83,9 +84,34 @@
MI->getOperand(0).getSubReg() == SubReg)
return true;
+ switch (MI->getOpcode()) {
+ case SystemZ::LR:
+ case SystemZ::LGR:
+ case SystemZ::LGFR:
+ case SystemZ::LTR:
+ case SystemZ::LTGR:
+ case SystemZ::LTGFR:
+ if (MI->getOperand(1).getReg() == Reg &&
+ MI->getOperand(1).getSubReg() == SubReg)
+ return true;
+ }
+
return false;
}
+// If MI is a load instruction, try to convert it into a LOAD AND TEST.
+// Return true on success.
+bool SystemZElimCompare::convertToLoadAndTest(MachineInstr *MI) {
+ unsigned Opcode = TII->getLoadAndTest(MI->getOpcode());
+ if (!Opcode)
+ return false;
+
+ MI->setDesc(TII->get(Opcode));
+ MachineInstrBuilder(*MI->getParent()->getParent(), MI)
+ .addReg(SystemZ::CC, RegState::ImplicitDefine);
+ return true;
+}
+
// The CC users in CCUsers are testing the result of a comparison of some
// value X against zero and we know that any CC value produced by MI
// would also reflect the value of X. Try to adjust CCUsers so that
@@ -184,17 +210,21 @@
unsigned SrcSubReg = Compare->getOperand(0).getSubReg();
MachineBasicBlock *MBB = Compare->getParent();
MachineBasicBlock::iterator MBBI = Compare, MBBE = MBB->begin();
+ bool SeenUseOfCC = false;
while (MBBI != MBBE) {
--MBBI;
MachineInstr *MI = MBBI;
if (resultTests(MI, SrcReg, SrcSubReg) &&
- adjustCCMasksForInstr(MI, Compare, CCUsers)) {
+ ((!SeenUseOfCC && convertToLoadAndTest(MI)) ||
+ adjustCCMasksForInstr(MI, Compare, CCUsers))) {
EliminatedComparisons += 1;
return true;
}
if (MI->modifiesRegister(SrcReg, TRI) ||
MI->modifiesRegister(SystemZ::CC, TRI))
return false;
+ if (MI->readsRegister(SystemZ::CC, TRI))
+ SeenUseOfCC = true;
}
return false;
}