The coalescer does not coalesce a virtual register to a physical register if any of the physical register's sub-register live intervals overlaps with the virtual register. This is overly conservative. It prevents a extract_subreg from being coalesced away:
v1024 = EDI // not killed
=
= EDI
One possible solution is for the coalescer to examine the sub-register live intervals in the same manner as the physical register. Another possibility is to examine defs and uses (when needed) of sub-registers. Both solutions are too expensive. For now, look for "short virtual intervals" and scan instructions to look for conflict instead.
This is a small win on x86-64. e.g. It shaves 403.gcc by ~80 instructions.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@61847 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/LiveIntervalAnalysis.cpp b/lib/CodeGen/LiveIntervalAnalysis.cpp
index 1900c1a..2259589 100644
--- a/lib/CodeGen/LiveIntervalAnalysis.cpp
+++ b/lib/CodeGen/LiveIntervalAnalysis.cpp
@@ -323,6 +323,47 @@
return false;
}
+/// conflictsWithPhysRegRef - Similar to conflictsWithPhysRegRef except
+/// it can check use as well.
+bool LiveIntervals::conflictsWithPhysRegRef(LiveInterval &li,
+ unsigned Reg, bool CheckUse,
+ SmallPtrSet<MachineInstr*,32> &JoinedCopies) {
+ for (LiveInterval::Ranges::const_iterator
+ I = li.ranges.begin(), E = li.ranges.end(); I != E; ++I) {
+ for (unsigned index = getBaseIndex(I->start),
+ end = getBaseIndex(I->end-1) + InstrSlots::NUM; index != end;
+ index += InstrSlots::NUM) {
+ // Skip deleted instructions.
+ MachineInstr *MI = 0;
+ while (index != end) {
+ MI = getInstructionFromIndex(index);
+ if (MI)
+ break;
+ index += InstrSlots::NUM;
+ }
+ if (index == end) break;
+
+ if (JoinedCopies.count(MI))
+ continue;
+ for (unsigned i = 0, e = MI->getNumOperands(); i != e; ++i) {
+ MachineOperand& MO = MI->getOperand(i);
+ if (!MO.isReg())
+ continue;
+ if (MO.isUse() && !CheckUse)
+ continue;
+ unsigned PhysReg = MO.getReg();
+ if (PhysReg == 0 || TargetRegisterInfo::isVirtualRegister(PhysReg))
+ continue;
+ if (tri_->isSubRegister(Reg, PhysReg))
+ return true;
+ }
+ }
+ }
+
+ return false;
+}
+
+
void LiveIntervals::printRegName(unsigned reg) const {
if (TargetRegisterInfo::isPhysicalRegister(reg))
cerr << tri_->getName(reg);
@@ -794,10 +835,15 @@
if (!VNI->copy)
return 0;
- if (VNI->copy->getOpcode() == TargetInstrInfo::EXTRACT_SUBREG)
- return VNI->copy->getOperand(1).getReg();
- if (VNI->copy->getOpcode() == TargetInstrInfo::INSERT_SUBREG)
+ if (VNI->copy->getOpcode() == TargetInstrInfo::EXTRACT_SUBREG) {
+ // If it's extracting out of a physical register, return the sub-register.
+ unsigned Reg = VNI->copy->getOperand(1).getReg();
+ if (TargetRegisterInfo::isPhysicalRegister(Reg))
+ Reg = tri_->getSubReg(Reg, VNI->copy->getOperand(2).getImm());
+ return Reg;
+ } else if (VNI->copy->getOpcode() == TargetInstrInfo::INSERT_SUBREG)
return VNI->copy->getOperand(2).getReg();
+
unsigned SrcReg, DstReg;
if (tii_->isMoveInstr(*VNI->copy, SrcReg, DstReg))
return SrcReg;