[StackMaps] Be explicit about label formation [NFC]

For auto-padding assembler support, we'll need to bundle the label with the instructions (nops or call sequences) so that they don't get separated.  This just rearranges the code to make the upcoming change more obvious.

include/llvm/CodeGen/StackMaps.h

@@ -266,13 +266,16 @@ public:
   /// Generate a stackmap record for a stackmap instruction.
   ///
   /// MI must be a raw STACKMAP, not a PATCHPOINT.
-  void recordStackMap(const MachineInstr &MI);
+  void recordStackMap(const MCSymbol &L,
+                      const MachineInstr &MI);
 
   /// Generate a stackmap record for a patchpoint instruction.
-  void recordPatchPoint(const MachineInstr &MI);
+  void recordPatchPoint(const MCSymbol &L,
+                        const MachineInstr &MI);
 
   /// Generate a stackmap record for a statepoint instruction.
-  void recordStatepoint(const MachineInstr &MI);
+  void recordStatepoint(const MCSymbol &L,
+                        const MachineInstr &MI);
 
   /// If there is any stack map data, create a stack map section and serialize
   /// the map info into it. This clears the stack map data structures
@@ -306,12 +309,15 @@ private:
   /// registers that need to be recorded in the stackmap.
   LiveOutVec parseRegisterLiveOutMask(const uint32_t *Mask) const;
 
-  /// This should be called by the MC lowering code _immediately_ before
-  /// lowering the MI to an MCInst. It records where the operands for the
-  /// instruction are stored, and outputs a label to record the offset of
-  /// the call from the start of the text section. In special cases (e.g. AnyReg
-  /// calling convention) the return register is also recorded if requested.
-  void recordStackMapOpers(const MachineInstr &MI, uint64_t ID,
+  /// Record the locations of the operands of the provided instruction in a
+  /// record keyed by the provided label.  For instructions w/AnyReg calling
+  /// convention the return register is also recorded if requested.  For
+  /// STACKMAP, and PATCHPOINT the label is expected to immediately *preceed*
+  /// lowering of the MI to MCInsts.  For STATEPOINT, it expected to
+  /// immediately *follow*.  It's not clear this difference was intentional,
+  /// but it exists today.  
+  void recordStackMapOpers(const MCSymbol &L,
+                           const MachineInstr &MI, uint64_t ID,
                            MachineInstr::const_mop_iterator MOI,
                            MachineInstr::const_mop_iterator MOE,
                            bool recordResult = false);

lib/CodeGen/StackMaps.cpp

@@ -294,14 +294,13 @@ StackMaps::parseRegisterLiveOutMask(const uint32_t *Mask) const {
   return LiveOuts;
 }
 
-void StackMaps::recordStackMapOpers(const MachineInstr &MI, uint64_t ID,
+void StackMaps::recordStackMapOpers(const MCSymbol &MILabel,
+                                    const MachineInstr &MI, uint64_t ID,
                                     MachineInstr::const_mop_iterator MOI,
                                     MachineInstr::const_mop_iterator MOE,
                                     bool recordResult) {
   MCContext &OutContext = AP.OutStreamer->getContext();
-  MCSymbol *MILabel = OutContext.createTempSymbol();
-  AP.OutStreamer->EmitLabel(MILabel);
-
+  
   LocationVec Locations;
   LiveOutVec LiveOuts;
 
@@ -340,7 +339,7 @@ void StackMaps::recordStackMapOpers(const MachineInstr &MI, uint64_t ID,
   // Create an expression to calculate the offset of the callsite from function
   // entry.
   const MCExpr *CSOffsetExpr = MCBinaryExpr::createSub(
-      MCSymbolRefExpr::create(MILabel, OutContext),
+      MCSymbolRefExpr::create(&MILabel, OutContext),
       MCSymbolRefExpr::create(AP.CurrentFnSymForSize, OutContext), OutContext);
 
   CSInfos.emplace_back(CSOffsetExpr, ID, std::move(Locations),
@@ -360,22 +359,23 @@ void StackMaps::recordStackMapOpers(const MachineInstr &MI, uint64_t ID,
     FnInfos.insert(std::make_pair(AP.CurrentFnSym, FunctionInfo(FrameSize)));
 }
 
-void StackMaps::recordStackMap(const MachineInstr &MI) {
+void StackMaps::recordStackMap(const MCSymbol &L, const MachineInstr &MI) {
   assert(MI.getOpcode() == TargetOpcode::STACKMAP && "expected stackmap");
 
   StackMapOpers opers(&MI);
   const int64_t ID = MI.getOperand(PatchPointOpers::IDPos).getImm();
-  recordStackMapOpers(MI, ID, std::next(MI.operands_begin(), opers.getVarIdx()),
+  recordStackMapOpers(L, MI, ID, std::next(MI.operands_begin(),
+                                           opers.getVarIdx()),
                       MI.operands_end());
 }
 
-void StackMaps::recordPatchPoint(const MachineInstr &MI) {
+void StackMaps::recordPatchPoint(const MCSymbol &L, const MachineInstr &MI) {
   assert(MI.getOpcode() == TargetOpcode::PATCHPOINT && "expected patchpoint");
 
   PatchPointOpers opers(&MI);
   const int64_t ID = opers.getID();
   auto MOI = std::next(MI.operands_begin(), opers.getStackMapStartIdx());
-  recordStackMapOpers(MI, ID, MOI, MI.operands_end(),
+  recordStackMapOpers(L, MI, ID, MOI, MI.operands_end(),
                       opers.isAnyReg() && opers.hasDef());
 
 #ifndef NDEBUG
@@ -390,14 +390,14 @@ void StackMaps::recordPatchPoint(const MachineInstr &MI) {
 #endif
 }
 
-void StackMaps::recordStatepoint(const MachineInstr &MI) {
+void StackMaps::recordStatepoint(const MCSymbol &L, const MachineInstr &MI) {
   assert(MI.getOpcode() == TargetOpcode::STATEPOINT && "expected statepoint");
 
   StatepointOpers opers(&MI);
   // Record all the deopt and gc operands (they're contiguous and run from the
   // initial index to the end of the operand list)
   const unsigned StartIdx = opers.getVarIdx();
-  recordStackMapOpers(MI, opers.getID(), MI.operands_begin() + StartIdx,
+  recordStackMapOpers(L, MI, opers.getID(), MI.operands_begin() + StartIdx,
                       MI.operands_end(), false);
 }
 

lib/Target/X86/X86MCInstLower.cpp

@@ -1194,7 +1194,10 @@ void X86AsmPrinter::LowerSTATEPOINT(const MachineInstr &MI,
 
   // Record our statepoint node in the same section used by STACKMAP
   // and PATCHPOINT
-  SM.recordStatepoint(MI);
+  auto &Ctx = OutStreamer->getContext();
+  MCSymbol *MILabel = Ctx.createTempSymbol();
+  OutStreamer->EmitLabel(MILabel);
+  SM.recordStatepoint(*MILabel, MI);
 }
 
 void X86AsmPrinter::LowerFAULTING_OP(const MachineInstr &FaultingMI,
@@ -1286,7 +1289,12 @@ void X86AsmPrinter::LowerPATCHABLE_OP(const MachineInstr &MI,
 // <id>, <shadowBytes>, ...
 void X86AsmPrinter::LowerSTACKMAP(const MachineInstr &MI) {
   SMShadowTracker.emitShadowPadding(*OutStreamer, getSubtargetInfo());
-  SM.recordStackMap(MI);
+
+  auto &Ctx = OutStreamer->getContext();
+  MCSymbol *MILabel = Ctx.createTempSymbol();
+  OutStreamer->EmitLabel(MILabel);
+
+  SM.recordStackMap(*MILabel, MI);
   unsigned NumShadowBytes = MI.getOperand(1).getImm();
   SMShadowTracker.reset(NumShadowBytes);
 }
@@ -1299,7 +1307,10 @@ void X86AsmPrinter::LowerPATCHPOINT(const MachineInstr &MI,
 
   SMShadowTracker.emitShadowPadding(*OutStreamer, getSubtargetInfo());
 
-  SM.recordPatchPoint(MI);
+  auto &Ctx = OutStreamer->getContext();
+  MCSymbol *MILabel = Ctx.createTempSymbol();
+  OutStreamer->EmitLabel(MILabel);
+  SM.recordPatchPoint(*MILabel, MI);
 
   PatchPointOpers opers(&MI);
   unsigned ScratchIdx = opers.getNextScratchIdx();