Extract method for detecting constant unallocatable physregs.

It is safe to move uses of such registers.

llvm-svn: 148259

1 files changed, 18 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineRegisterInfo.cpp b/llvm/lib/CodeGen/MachineRegisterInfo.cpp
index 67291a0eb8c..6ec55247bf0 100644
--- a/llvm/lib/CodeGen/MachineRegisterInfo.cpp
+++ b/llvm/lib/CodeGen/MachineRegisterInfo.cpp
@@ -263,3 +263,21 @@ void MachineRegisterInfo::dumpUses(unsigned Reg) const {
 void MachineRegisterInfo::freezeReservedRegs(const MachineFunction &MF) {
   ReservedRegs = TRI->getReservedRegs(MF);
 }
+
+bool MachineRegisterInfo::isConstantPhysReg(unsigned PhysReg,
+                                            const MachineFunction &MF) const {
+  assert(TargetRegisterInfo::isPhysicalRegister(PhysReg));
+
+  // Check if any overlapping register is modified.
+  for (const unsigned *R = TRI->getOverlaps(PhysReg); *R; ++R)
+    if (!def_empty(*R))
+      return false;
+
+  // Check if any overlapping register is allocatable so it may be used later.
+  if (AllocatableRegs.empty())
+    AllocatableRegs = TRI->getAllocatableSet(MF);
+  for (const unsigned *R = TRI->getOverlaps(PhysReg); *R; ++R)
+    if (AllocatableRegs.test(*R))
+      return false;
+  return true;
+}