Make it possible to have unallocatable register classes.

Some register classes are only used for instruction operand constraints.
They should never be used for virtual registers. Previously, those
register classes were given an empty allocation order, but now you can
say 'let isAllocatable=0' in the register class definition.

TableGen calculates if a register is part of any allocatable register
class, and makes that information available in TargetRegisterDesc::inAllocatableClass.

The goal here is to eliminate use cases for overriding allocation_order_*
methods.

llvm-svn: 132508

1 files changed, 2 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineRegisterInfo.cpp b/llvm/lib/CodeGen/MachineRegisterInfo.cpp
index 7244d5f03a9..08ff5bb7152 100644
--- a/llvm/lib/CodeGen/MachineRegisterInfo.cpp
+++ b/llvm/lib/CodeGen/MachineRegisterInfo.cpp
@@ -79,6 +79,8 @@ MachineRegisterInfo::constrainRegClass(unsigned Reg,
 unsigned
 MachineRegisterInfo::createVirtualRegister(const TargetRegisterClass *RegClass){
   assert(RegClass && "Cannot create register without RegClass!");
+  assert(RegClass->isAllocatable() &&
+         "Virtual register RegClass must be allocatable.");
 
   // New virtual register number.
   unsigned Reg = TargetRegisterInfo::index2VirtReg(getNumVirtRegs());