[IfConversion] More simple, correct dead/kill liveness handling
Patch by Jesper Antonsson.
Differential Revision: https://reviews.llvm.org/D37611
llvm-svn: 313268
diff --git a/llvm/lib/CodeGen/LivePhysRegs.cpp b/llvm/lib/CodeGen/LivePhysRegs.cpp
index c3e46d3..779f601 100644
--- a/llvm/lib/CodeGen/LivePhysRegs.cpp
+++ b/llvm/lib/CodeGen/LivePhysRegs.cpp
@@ -40,10 +40,8 @@
}
}
-/// Simulates liveness when stepping backwards over an instruction(bundle):
-/// Remove Defs, add uses. This is the recommended way of calculating liveness.
-void LivePhysRegs::stepBackward(const MachineInstr &MI) {
- // Remove defined registers and regmask kills from the set.
+/// Remove defined registers and regmask kills from the set.
+void LivePhysRegs::removeDefs(const MachineInstr &MI) {
for (ConstMIBundleOperands O(MI); O.isValid(); ++O) {
if (O->isReg()) {
if (!O->isDef())
@@ -55,8 +53,10 @@
} else if (O->isRegMask())
removeRegsInMask(*O);
}
+}
- // Add uses to the set.
+/// Add uses to the set.
+void LivePhysRegs::addUses(const MachineInstr &MI) {
for (ConstMIBundleOperands O(MI); O.isValid(); ++O) {
if (!O->isReg() || !O->readsReg())
continue;
@@ -67,6 +67,16 @@
}
}
+/// Simulates liveness when stepping backwards over an instruction(bundle):
+/// Remove Defs, add uses. This is the recommended way of calculating liveness.
+void LivePhysRegs::stepBackward(const MachineInstr &MI) {
+ // Remove defined registers and regmask kills from the set.
+ removeDefs(MI);
+
+ // Add uses to the set.
+ addUses(MI);
+}
+
/// Simulates liveness when stepping forward over an instruction(bundle): Remove
/// killed-uses, add defs. This is the not recommended way, because it depends
/// on accurate kill flags. If possible use stepBackward() instead of this
@@ -265,6 +275,53 @@
}
}
+void llvm::recomputeLivenessFlags(MachineBasicBlock &MBB) {
+ const MachineFunction &MF = *MBB.getParent();
+ const MachineRegisterInfo &MRI = MF.getRegInfo();
+ const TargetRegisterInfo &TRI = *MRI.getTargetRegisterInfo();
+
+ // We walk through the block backwards and start with the live outs.
+ LivePhysRegs LiveRegs;
+ LiveRegs.init(TRI);
+ LiveRegs.addLiveOutsNoPristines(MBB);
+
+ for (MachineInstr &MI : make_range(MBB.rbegin(), MBB.rend())) {
+ // Recompute dead flags.
+ for (MIBundleOperands MO(MI); MO.isValid(); ++MO) {
+ if (!MO->isReg() || !MO->isDef() || MO->isDebug())
+ continue;
+
+ unsigned Reg = MO->getReg();
+ if (Reg == 0)
+ continue;
+ assert(TargetRegisterInfo::isPhysicalRegister(Reg));
+
+ bool IsNotLive = LiveRegs.available(MRI, Reg);
+ MO->setIsDead(IsNotLive);
+ }
+
+ // Step backward over defs.
+ LiveRegs.removeDefs(MI);
+
+ // Recompute kill flags.
+ for (MIBundleOperands MO(MI); MO.isValid(); ++MO) {
+ if (!MO->isReg() || !MO->readsReg() || MO->isDebug())
+ continue;
+
+ unsigned Reg = MO->getReg();
+ if (Reg == 0)
+ continue;
+ assert(TargetRegisterInfo::isPhysicalRegister(Reg));
+
+ bool IsNotLive = LiveRegs.available(MRI, Reg);
+ MO->setIsKill(IsNotLive);
+ }
+
+ // Complete the stepbackward.
+ LiveRegs.addUses(MI);
+ }
+}
+
void llvm::computeAndAddLiveIns(LivePhysRegs &LiveRegs,
MachineBasicBlock &MBB) {
computeLiveIns(LiveRegs, MBB);