Fix live variables issues:
1. If part of a register is re-defined, an implicit kill and an implicit def are added to denote read / mod / write. However, this should only be necessary if the register is actually read later. This is a performance issue.
2. If a sub-register is being defined, and it doesn't have a previous use, do not add a implicit kill to the last use of a super-register:
= EAX, AX<imp-use,kill>
...
AX =
In this case, EAX is live but AX is killed, this is wrong and will cause the coalescer to do bad things.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48521 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/LiveVariables.cpp b/lib/CodeGen/LiveVariables.cpp
index 27f459d..35461ef 100644
--- a/lib/CodeGen/LiveVariables.cpp
+++ b/lib/CodeGen/LiveVariables.cpp
@@ -267,8 +267,9 @@
if (*SubRegs == 0) {
// No sub-registers, just check if reg is killed by RefMI.
- if (PhysRegInfo[Reg] == RefMI)
+ if (PhysRegInfo[Reg] == RefMI && PhysRegInfo[Reg]->readsRegister(Reg)) {
return true;
+ }
} else if (SubKills.empty()) {
// None of the sub-registers are killed elsewhere.
return true;
@@ -297,6 +298,34 @@
return false;
}
+/// hasRegisterUseBelow - Return true if the specified register is used after
+/// the current instruction and before it's next definition.
+bool LiveVariables::hasRegisterUseBelow(unsigned Reg,
+ MachineBasicBlock::iterator I,
+ MachineBasicBlock *MBB) {
+ if (I == MBB->end())
+ return false;
+ ++I;
+ // FIXME: This is slow. We probably need a smarter solution. Possibilities:
+ // 1. Scan all instructions once and build def / use information of physical
+ // registers. We also need a fast way to compare relative ordering of
+ // instructions.
+ // 2. Cache information so this function only has to scan instructions that
+ // read / def physical instructions.
+ for (MachineBasicBlock::iterator E = MBB->end(); I != E; ++I) {
+ MachineInstr *MI = I;
+ for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+ const MachineOperand &MO = MI->getOperand(i);
+ if (!MO.isRegister() || MO.getReg() != Reg)
+ continue;
+ if (MO.isDef())
+ return false;
+ return true;
+ }
+ }
+ return false;
+}
+
void LiveVariables::HandlePhysRegDef(unsigned Reg, MachineInstr *MI) {
// Does this kill a previous version of this register?
if (MachineInstr *LastRef = PhysRegInfo[Reg]) {
@@ -338,14 +367,22 @@
unsigned SuperReg = *SuperRegs; ++SuperRegs) {
if (PhysRegInfo[SuperReg] && PhysRegInfo[SuperReg] != MI) {
// The larger register is previously defined. Now a smaller part is
- // being re-defined. Treat it as read/mod/write.
+ // being re-defined. Treat it as read/mod/write if there are uses
+ // below.
// EAX =
// AX = EAX<imp-use,kill>, EAX<imp-def>
- MI->addOperand(MachineOperand::CreateReg(SuperReg, false/*IsDef*/,
+ // ...
+ /// = EAX
+ if (MI && hasRegisterUseBelow(SuperReg, MI, MI->getParent())) {
+ MI->addOperand(MachineOperand::CreateReg(SuperReg, false/*IsDef*/,
true/*IsImp*/,true/*IsKill*/));
- MI->addOperand(MachineOperand::CreateReg(SuperReg, true/*IsDef*/,
- true/*IsImp*/));
- PhysRegInfo[SuperReg] = MI;
+ MI->addOperand(MachineOperand::CreateReg(SuperReg, true/*IsDef*/,
+ true/*IsImp*/));
+ PhysRegInfo[SuperReg] = MI;
+ } else {
+ PhysRegInfo[SuperReg]->addRegisterKilled(SuperReg, TRI, true);
+ PhysRegInfo[SuperReg] = NULL;
+ }
PhysRegUsed[SuperReg] = false;
PhysRegPartUse[SuperReg] = NULL;
} else {