[Stackmap] Liveness Analysis Pass

This optional register liveness analysis pass can be enabled with either
-enable-stackmap-liveness, -enable-patchpoint-liveness, or both. The pass
traverses each basic block in a machine function. For each basic block the
instructions are processed in reversed order and if a patchpoint or stackmap
instruction is encountered the current live-out register set is encoded as a
register mask and attached to the instruction.

Later on during stackmap generation the live-out register mask is processed and
also emitted as part of the stackmap.

This information is optional and intended for optimization purposes only. This
will enable a client of the stackmap to reason about the registers it can use
and which registers need to be preserved.

Reviewed by Andy

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197317 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineFunction.h

@@ -426,6 +426,15 @@ public:
     OperandRecycler.deallocate(Cap, Array);
   }
 
+  /// \brief Allocate and initialize a register mask with @p NumRegister bits.
+  uint32_t *allocateRegisterMask(unsigned NumRegister) {
+    unsigned Size = (NumRegister + 31) / 32;
+    uint32_t *Mask = Allocator.Allocate<uint32_t>(Size);
+    for (unsigned i = 0; i != Size; ++i)
+      Mask[i] = 0;
+    return Mask;
+  }
+
   /// allocateMemRefsArray - Allocate an array to hold MachineMemOperand
   /// pointers.  This array is owned by the MachineFunction.
   MachineInstr::mmo_iterator allocateMemRefsArray(unsigned long Num);