[llvm] [msan] Handle Arm NEON saturating extract and narrow (PR #125742)

[Thurston Dang via llvm-commits]

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@@ -4749,6 +4749,13 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
       setOrigin(&I, getCleanOrigin());
       break;
 
+    // Saturating extract narrow
+    case Intrinsic::aarch64_neon_sqxtn:
+    case Intrinsic::aarch64_neon_sqxtun:
+    case Intrinsic::aarch64_neon_uqxtn:
+      handleShadowOr(I);
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thurstond wrote:

> Isn't the output only half as long as the original? Don't we need to account for that?

That's why I use handleShadowOr - it will perform the cast.

>From the test output:
```
; CHECK-NEXT:    [[_MSPROP1:%.*]] = or <8 x i16> [[TMP1]], zeroinitializer
; CHECK-NEXT:    [[TMP5:%.*]] = trunc <8 x i16> [[_MSPROP1]] to <8 x i8>
```

> Also, it is confusing that you use handleShadowOr on a single argument instruction. At least leave a comment that explains.

I've added a comment.


https://github.com/llvm/llvm-project/pull/125742