[msan] Make -msan-check-constant-shadow a bit stronger.

Allow (under the experimental flag) non-Instructions to participate in MSan checks.

llvm-svn: 220601

2 files changed, 25 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
index 9f20b66f7bb..4a7669fe5d0 100644
--- a/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -1062,9 +1062,16 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
   /// UMR warning in runtime if the value is not fully defined.
   void insertShadowCheck(Value *Val, Instruction *OrigIns) {
     assert(Val);
-    Instruction *Shadow = dyn_cast_or_null<Instruction>(getShadow(Val));
-    if (!Shadow) return;
-    Instruction *Origin = dyn_cast_or_null<Instruction>(getOrigin(Val));
+    Value *Shadow, *Origin;
+    if (ClCheckConstantShadow) {
+      Shadow = getShadow(Val);
+      if (!Shadow) return;
+      Origin = getOrigin(Val);
+    } else {
+      Shadow = dyn_cast_or_null<Instruction>(getShadow(Val));
+      if (!Shadow) return;
+      Origin = dyn_cast_or_null<Instruction>(getOrigin(Val));
+    }
     insertShadowCheck(Shadow, Origin, OrigIns);
   }
 
diff --git a/llvm/test/Instrumentation/MemorySanitizer/check-constant-shadow.ll b/llvm/test/Instrumentation/MemorySanitizer/check-constant-shadow.ll
new file mode 100644
index 00000000000..11e44106d8f
--- /dev/null
+++ b/llvm/test/Instrumentation/MemorySanitizer/check-constant-shadow.ll
@@ -0,0 +1,15 @@
+; RUN: opt < %s -msan -msan-check-constant-shadow=1 -S | FileCheck %s
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Test that returning a literal undef from main() triggers an MSan warning.
+
+define i32 @main() nounwind uwtable sanitize_memory {
+entry:
+  ret i32 undef
+}
+
+; CHECK-LABEL: @main
+; CHECK: call void @__msan_warning_noreturn
+; CHECK: ret i32 undef