2 files changed, 19 insertions, 7 deletions

diff --git a/llvm/lib/Target/X86/X86AsmPrinter.h b/llvm/lib/Target/X86/X86AsmPrinter.h
index 4b9913c01e63..fdec333b6934 100644
--- a/llvm/lib/Target/X86/X86AsmPrinter.h
+++ b/llvm/lib/Target/X86/X86AsmPrinter.h
@@ -44,16 +44,27 @@ class LLVM_LIBRARY_VISIBILITY X86AsmPrinter : public AsmPrinter {
     ~StackMapShadowTracker();
     void startFunction(MachineFunction &MF);
     void count(MCInst &Inst, const MCSubtargetInfo &STI);
+
+    // Called to signal the start of a shadow of RequiredSize bytes.
     void reset(unsigned RequiredSize) {
       RequiredShadowSize = RequiredSize;
       CurrentShadowSize = 0;
-      Count = true;
+      InShadow = true;
     }
+
+    // Called before every stackmap/patchpoint, and at the end of basic blocks,
+    // to emit any necessary padding-NOPs.
     void emitShadowPadding(MCStreamer &OutStreamer, const MCSubtargetInfo &STI);
   private:
     TargetMachine &TM;
     std::unique_ptr<MCCodeEmitter> CodeEmitter;
-    bool Count;
+    bool InShadow;
+
+    // RequiredShadowSize holds the length of the shadow specified in the most
+    // recently encountered STACKMAP instruction.
+    // CurrentShadowSize counts the number of bytes encoded since the most
+    // recently encountered STACKMAP, stopping when that number is greater than
+    // or equal to RequiredShadowSize.
     unsigned RequiredShadowSize, CurrentShadowSize;
   };
 
diff --git a/llvm/lib/Target/X86/X86MCInstLower.cpp b/llvm/lib/Target/X86/X86MCInstLower.cpp
index 4b55f00db639..96ab70a29a37 100644
--- a/llvm/lib/Target/X86/X86MCInstLower.cpp
+++ b/llvm/lib/Target/X86/X86MCInstLower.cpp
@@ -66,7 +66,7 @@ static void EmitNops(MCStreamer &OS, unsigned NumBytes, bool Is64Bit,
 
 namespace llvm {
    X86AsmPrinter::StackMapShadowTracker::StackMapShadowTracker(TargetMachine &TM)
-     : TM(TM), Count(false), RequiredShadowSize(0), CurrentShadowSize(0) {}
+     : TM(TM), InShadow(false), RequiredShadowSize(0), CurrentShadowSize(0) {}
 
   X86AsmPrinter::StackMapShadowTracker::~StackMapShadowTracker() {}
 
@@ -80,7 +80,7 @@ namespace llvm {
 
   void X86AsmPrinter::StackMapShadowTracker::count(MCInst &Inst,
                                                    const MCSubtargetInfo &STI) {
-    if (Count) {
+    if (InShadow) {
       SmallString<256> Code;
       SmallVector<MCFixup, 4> Fixups;
       raw_svector_ostream VecOS(Code);
@@ -88,16 +88,17 @@ namespace llvm {
       VecOS.flush();
       CurrentShadowSize += Code.size();
       if (CurrentShadowSize >= RequiredShadowSize)
-        Count = false; // The shadow is big enough. Stop counting.
+        InShadow = false; // The shadow is big enough. Stop counting.
     }
   }
 
   void X86AsmPrinter::StackMapShadowTracker::emitShadowPadding(
     MCStreamer &OutStreamer, const MCSubtargetInfo &STI) {
-    if (Count && CurrentShadowSize < RequiredShadowSize)
+    if (InShadow && CurrentShadowSize < RequiredShadowSize) {
+      InShadow = false;
       EmitNops(OutStreamer, RequiredShadowSize - CurrentShadowSize,
                TM.getSubtarget<X86Subtarget>().is64Bit(), STI);
-    Count = false;
+    }
   }
 
   void X86AsmPrinter::EmitAndCountInstruction(MCInst &Inst) {