Make the control point accept a pointer to a YkLocation.

Currently the JIT identifies a user-program location using a simple
integer, but it should use the `YkLocation` struct, which would allow
for more realistic control point behaviour (hot counts etc.).

This change modifies the type of the patched-in control point (and its
call-site) to use `YkLocation`.

Note that the control point is still very simple and uses the addresses
of YkLocations as an identifier. This is not how we intend this to work
in the long run: YkLocations should be freely moveable (see
`location.rs` for our preliminary intent from the old yk design).

Needless to say, for now we also bypass all of YkLocation's
multi-threaded synchronisation too.

Author: vext01

llvm/lib/Transforms/Yk/ControlPoint.cpp

@@ -46,10 +46,11 @@
 // YKFIXME: The control point cannot yet be used in an interpreter using
 // threaded dispatch.
 //
-// YKFIXME: The tracing logic is currently over-simplified:
+// YKFIXME: The tracing logic is currently over-simplified. The following items
+// need to be fixed:
 //
-//  - A JIT location is assumed to be a simple integer program counter. It
-//    should be a `ykrt::Location`.
+//  - The address of `YkLocation` instances are used for identity, but they are
+//    intended to be freely moved by the user.
 //
 //  - Tracing starts when we encounter a location for which we have no machine
 //    code. A hot counter should be used instead.
@@ -123,7 +124,7 @@ void createJITStatePrint(IRBuilder<> &Builder, Module *Mod, std::string Str) {
 /// Generates the new control point, which includes all logic to start/stop
 /// tracing and to compile/execute traces.
 void createControlPoint(Module &Mod, Function *F, std::vector<Value *> LiveVars,
-                        StructType *YkCtrlPointStruct) {
+                        StructType *YkCtrlPointStruct, Type *YkLocTy) {
   auto &Context = Mod.getContext();
 
   // Create control point blocks and setup the IRBuilder.
@@ -166,9 +167,8 @@ void createControlPoint(Module &Mod, Function *F, std::vector<Value *> LiveVars,
       PtNull, "compiled_trace", (GlobalVariable *)nullptr);
 
   GlobalVariable *GVStartLoc = new GlobalVariable(
-      Mod, Type::getInt32Ty(Context), false, GlobalVariable::InternalLinkage,
-      ConstantInt::get(Context, APInt(32, -1)), "start_loc",
-      (GlobalVariable *)nullptr);
+      Mod, YkLocTy, false, GlobalVariable::InternalLinkage,
+      Constant::getNullValue(YkLocTy), "start_loc", (GlobalVariable *)nullptr);
 
   // Create control point entry block. Checks if we are currently tracing.
   Value *GVTracingVal = Builder.CreateLoad(Type::getInt8Ty(Context), GVTracing);
@@ -196,8 +196,7 @@ void createControlPoint(Module &Mod, Function *F, std::vector<Value *> LiveVars,
   // Create block that checks if we've reached the same location again so we
   // can execute a compiled trace.
   Builder.SetInsertPoint(BBHasTrace);
-  Value *ValStartLoc =
-      Builder.CreateLoad(Type::getInt32Ty(Context), GVStartLoc);
+  Value *ValStartLoc = Builder.CreateLoad(YkLocTy, GVStartLoc);
   Value *ExecTraceCond = Builder.CreateICmp(CmpInst::Predicate::ICMP_EQ,
                                             ValStartLoc, F->getArg(0));
   Builder.CreateCondBr(ExecTraceCond, BBExecuteTrace, BBReturn);
@@ -220,8 +219,7 @@ void createControlPoint(Module &Mod, Function *F, std::vector<Value *> LiveVars,
 
   // Create block that decides when to stop tracing.
   Builder.SetInsertPoint(BBTracing);
-  Value *ValStartLoc2 =
-      Builder.CreateLoad(Type::getInt32Ty(Context), GVStartLoc);
+  Value *ValStartLoc2 = Builder.CreateLoad(YkLocTy, GVStartLoc);
   Value *StopTracingCond = Builder.CreateICmp(CmpInst::Predicate::ICMP_EQ,
                                               ValStartLoc2, F->getArg(0));
   Builder.CreateCondBr(StopTracingCond, BBStopTracing, BBReturn);
@@ -312,8 +310,9 @@ PreservedAnalyses YkControlPointPass::run(Module &M,
       StructType::create(TypeParams, "YkCtrlPointVars");
 
   // Create the new control point.
-  FunctionType *FType = FunctionType::get(
-      CtrlPointReturnTy, {Type::getInt32Ty(Context), CtrlPointReturnTy}, false);
+  Type *YkLocTy = OldCtrlPointCall->getArgOperand(0)->getType();
+  FunctionType *FType =
+      FunctionType::get(CtrlPointReturnTy, {YkLocTy, CtrlPointReturnTy}, false);
   Function *NF = Function::Create(FType, GlobalVariable::ExternalLinkage,
                                   YK_NEW_CONTROL_POINT, M);
 
@@ -347,7 +346,7 @@ PreservedAnalyses YkControlPointPass::run(Module &M,
   OldCtrlPointCall->eraseFromParent();
 
   // Generate new control point logic.
-  createControlPoint(M, NF, LiveVals, CtrlPointReturnTy);
+  createControlPoint(M, NF, LiveVals, CtrlPointReturnTy, YkLocTy);
 
   return PreservedAnalyses::none();
 }