ARM: Fix optimizeCompare to correctly check safe condition.
It is safe if CPSR is killed or re-defined.
When we are done with the basic block, check whether CPSR is live-out.
Do not optimize away cmp if CPSR is live-out.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160090 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/ARM/ARMBaseInstrInfo.cpp b/lib/Target/ARM/ARMBaseInstrInfo.cpp
index 57c20ae..3393f09 100644
--- a/lib/Target/ARM/ARMBaseInstrInfo.cpp
+++ b/lib/Target/ARM/ARMBaseInstrInfo.cpp
@@ -1974,10 +1974,10 @@
case ARM::t2EORri: {
// Scan forward for the use of CPSR
// When checking against MI: if it's a conditional code requires
- // checking of V bit, then this is not safe to do. If we can't find the
- // CPSR use (i.e. used in another block), then it's not safe to perform
- // the optimization.
- // When checking against Sub, we handle the condition codes GE, LT, GT, LE.
+ // checking of V bit, then this is not safe to do.
+ // It is safe to remove CmpInstr if CPSR is redefined or killed.
+ // If we are done with the basic block, we need to check whether CPSR is
+ // live-out.
SmallVector<std::pair<MachineOperand*, ARMCC::CondCodes>, 4>
OperandsToUpdate;
bool isSafe = false;
@@ -2017,7 +2017,7 @@
else
switch (CC) {
default:
- isSafe = true;
+ // CPSR can be used mutliple times, we should continue.
break;
case ARMCC::VS:
case ARMCC::VC:
@@ -2030,10 +2030,15 @@
}
}
- // If the candidate is Sub, we may exit the loop at end of the basic block.
- // In that case, it is still safe to remove CmpInstr.
- if (!isSafe && !Sub)
- return false;
+ // If CPSR is not killed nor re-defined, we should check whether it is
+ // live-out. If it is live-out, do not optimize.
+ if (!isSafe) {
+ MachineBasicBlock *MBB = CmpInstr->getParent();
+ for (MachineBasicBlock::succ_iterator SI = MBB->succ_begin(),
+ SE = MBB->succ_end(); SI != SE; ++SI)
+ if ((*SI)->isLiveIn(ARM::CPSR))
+ return false;
+ }
// Toggle the optional operand to CPSR.
MI->getOperand(5).setReg(ARM::CPSR);