diff --git a/test/CodeGen/X86/stackmap-nops.ll b/test/CodeGen/X86/stackmap-nops.ll
index 3888603c969..7de63af852a 100644
--- a/test/CodeGen/X86/stackmap-nops.ll
+++ b/test/CodeGen/X86/stackmap-nops.ll
@@ -224,6 +224,9 @@ entry:
   tail call void (i64, i32, ...)* @llvm.experimental.stackmap(i64 28, i32 28)
   tail call void (i64, i32, ...)* @llvm.experimental.stackmap(i64 29, i32 29)
   tail call void (i64, i32, ...)* @llvm.experimental.stackmap(i64 30, i32 30)
+; Add an extra stackmap with a zero-length shadow to thwart the shadow
+; optimization. This will force all 15 bytes of the previous shadow to be
+; padded with nops.
   tail call void (i64, i32, ...)* @llvm.experimental.stackmap(i64 31, i32 0)
   ret void
 }
diff --git a/test/MC/X86/stackmap-nops.ll b/test/MC/X86/stackmap-nops.ll
index 2b0b88c80fa..a0d44186603 100644
--- a/test/MC/X86/stackmap-nops.ll
+++ b/test/MC/X86/stackmap-nops.ll
@@ -41,6 +41,9 @@ entry:
   tail call void (i64, i32, ...)* @llvm.experimental.stackmap(i64 13, i32 13)
   tail call void (i64, i32, ...)* @llvm.experimental.stackmap(i64 14, i32 14)
   tail call void (i64, i32, ...)* @llvm.experimental.stackmap(i64 15, i32 15)
+; Add an extra stackmap with a zero-length shadow to thwart the shadow
+; optimization. This will force all 15 bytes of the previous shadow to be
+; padded with nops.
   tail call void (i64, i32, ...)* @llvm.experimental.stackmap(i64 16, i32 0)
   ret void
 }