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

This handles NEON saturating extract and narrow (Intrinsic::aarch64_neon_{sqxtn, sqxtun, uqxtn}) by (ab)using handleShadowOr() to perform the shadow cast. Previously, these were unknown intrinsics handled suboptimally by visitInstruction.

Updates the tests from llvm#125288 and llvm#125140

Author: thurstond

llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp

@@ -4894,6 +4894,16 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
       break;
     }
 
+    // Saturating extract narrow
+    case Intrinsic::aarch64_neon_sqxtn:
+    case Intrinsic::aarch64_neon_sqxtun:
+    case Intrinsic::aarch64_neon_uqxtn:
+      // These only have one argument, but we (ab)use handleShadowOr because it
+      // does work on single argument intrinsics and will typecast the shadow
+      // (and update the origin).
+      handleShadowOr(I);
+      break;
+
     case Intrinsic::aarch64_neon_st1x2:
     case Intrinsic::aarch64_neon_st1x3:
     case Intrinsic::aarch64_neon_st1x4: