Index: lib/Transforms/Instrumentation/MemorySanitizer.cpp
===================================================================
--- lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -3099,6 +3099,12 @@
       handleVectorComparePackedIntrinsic(I);
       break;
 
+    case Intrinsic::is_constant:
+      // The result of llvm.is.constant() is always defined.
+      setShadow(&I, getCleanShadow(&I));
+      setOrigin(&I, getCleanOrigin());
+      break;
+
     default:
       if (!handleUnknownIntrinsic(I))
         visitInstruction(I);
Index: test/Instrumentation/MemorySanitizer/msan_llvm_is_constant.ll
===================================================================
--- test/Instrumentation/MemorySanitizer/msan_llvm_is_constant.ll
+++ test/Instrumentation/MemorySanitizer/msan_llvm_is_constant.ll
@@ -0,0 +1,21 @@
+; Make sure MSan doesn't insert shadow checks for @llvm.is.constant.* arguments.
+
+; RUN: opt < %s -msan -msan-kernel=1 -S | FileCheck -check-prefixes=CHECK %s
+; RUN: opt < %s -msan -S | FileCheck -check-prefixes=CHECK %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: nounwind readnone uwtable
+define dso_local i32 @bar(i32 %v) local_unnamed_addr sanitize_memory {
+entry:
+  %0 = tail call i1 @llvm.is.constant.i32(i32 %v)
+  %1 = zext i1 %0 to i32
+  ret i32 %1
+}
+
+; CHECK-LABEL: bar
+; CHECK-NOT: call void @__msan_warning
+
+; Function Attrs: nounwind readnone
+declare i1 @llvm.is.constant.i32(i32)