[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/Passes.h

@@ -568,6 +568,11 @@ namespace llvm {
   /// bundles (created earlier, e.g. during pre-RA scheduling).
   extern char &FinalizeMachineBundlesID;
 
+  /// StackMapLiveness - This pass analyses the register live-out set of
+  /// stackmap/patchpoint intrinsics and attaches the calculated information to
+  /// the intrinsic for later emission to the StackMap.
+  extern char &StackMapLivenessID;
+
 } // End llvm namespace
 
 #endif