[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

lib/CodeGen/CodeGen.cpp

@@ -69,6 +69,7 @@ void llvm::initializeCodeGen(PassRegistry &Registry) {
   initializeVirtRegRewriterPass(Registry);
   initializeLowerIntrinsicsPass(Registry);
   initializeMachineFunctionPrinterPassPass(Registry);
+  initializeStackMapLivenessPass(Registry);
 }
 
 void LLVMInitializeCodeGen(LLVMPassRegistryRef R) {