Stackmap shadows should consider call returns a branch target.

To avoid emitting too many nops, a stackmap shadow can include emitted instructions in the shadow, but these must not include branch targets.

A return from a call should count as a branch target as patching over the instructions after the call would lead to incorrect behaviour for threads currently making that call, when they return.

llvm-svn: 220710

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86MCInstLower.cpp b/llvm/lib/Target/X86/X86MCInstLower.cpp
index fc3662e6bec..85cf5144f0c 100644
--- a/llvm/lib/Target/X86/X86MCInstLower.cpp
+++ b/llvm/lib/Target/X86/X86MCInstLower.cpp
@@ -1210,4 +1210,10 @@ void X86AsmPrinter::EmitInstruction(const MachineInstr *MI) {
   MCInst TmpInst;
   MCInstLowering.Lower(MI, TmpInst);
   EmitAndCountInstruction(TmpInst);
+
+  // Stackmap shadows cannot include branch targets, so we can count the bytes
+  // in a call towards the shadow, but must flush the shadow immediately after
+  // to account for the return from the call.
+  if (MI->isCall())
+    SMShadowTracker.emitShadowPadding(OutStreamer, getSubtargetInfo());
 }