[msan] Handle single-parameter Arm NEON vector convert intrinsics (#1…

…26136)

This handles the following llvm.aarch64.neon intrinsics, which were suboptimally handled by visitInstruction:
- fcvtas, fcvtau
- fcvtms, fcvtmu
- fcvtns, fcvtnu
- fcvtps, fcvtpu
- fcvtzs, fcvtzu

The old instrumentation checked that the shadow of every element of the input vector was fully initialized, and aborted otherwise. The new instrumentation propagates the shadow: for each element of the output, the shadow is initialized iff the corresponding element of the input is *fully* initialized (since these are floating-point to integer conversions).

Updates the tests from llvm/llvm-project#126095

llvm/lib/Transforms/Instrumentation/MemorySanitizer.cpp

@@ -3172,7 +3172,31 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
     setOriginForNaryOp(I);
   }
 
-  // Instrument vector convert intrinsic.
+  /// Handle Arm NEON vector convert intrinsics.
+  ///
+  /// e.g., <4 x i32> @llvm.aarch64.neon.fcvtpu.v4i32.v4f32(<4 x float>)
+  ///      i32 @llvm.aarch64.neon.fcvtms.i32.f64(double)
+  ///
+  /// For x86 SSE vector convert intrinsics, see
+  /// handleSSEVectorConvertIntrinsic().
+  void handleNEONVectorConvertIntrinsic(IntrinsicInst &I) {
+    assert(I.arg_size() == 1);
+
+    IRBuilder<> IRB(&I);
+    Value *S0 = getShadow(&I, 0);
+
+    /// For scalars:
+    /// Since they are converting from floating-point to integer, the output is
+    /// - fully uninitialized if *any* bit of the input is uninitialized
+    /// - fully ininitialized if all bits of the input are ininitialized
+    /// We apply the same principle on a per-field basis for vectors.
+    Value *OutShadow = IRB.CreateSExt(IRB.CreateICmpNE(S0, getCleanShadow(S0)),
+                                      getShadowTy(&I));
+    setShadow(&I, OutShadow);
+    setOriginForNaryOp(I);
+  }
+
+  // Instrument x86 SSE vector convert intrinsic.
   //
   // This function instruments intrinsics like cvtsi2ss:
   // %Out = int_xxx_cvtyyy(%ConvertOp)
@@ -3187,8 +3211,11 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
   // We copy the shadow of \p CopyOp[NumUsedElements:] to \p
   // Out[NumUsedElements:]. This means that intrinsics without \p CopyOp always
   // return a fully initialized value.
-  void handleVectorConvertIntrinsic(IntrinsicInst &I, int NumUsedElements,
-                                    bool HasRoundingMode = false) {
+  //
+  // For Arm NEON vector convert intrinsics, see
+  // handleNEONVectorConvertIntrinsic().
+  void handleSSEVectorConvertIntrinsic(IntrinsicInst &I, int NumUsedElements,
+                                       bool HasRoundingMode = false) {
     IRBuilder<> IRB(&I);
     Value *CopyOp, *ConvertOp;
 
@@ -4477,7 +4504,7 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
     case Intrinsic::x86_avx512_cvtusi2ss:
     case Intrinsic::x86_avx512_cvtusi642sd:
     case Intrinsic::x86_avx512_cvtusi642ss:
-      handleVectorConvertIntrinsic(I, 1, true);
+      handleSSEVectorConvertIntrinsic(I, 1, true);
       break;
     case Intrinsic::x86_sse2_cvtsd2si64:
     case Intrinsic::x86_sse2_cvtsd2si:
@@ -4488,11 +4515,11 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
     case Intrinsic::x86_sse_cvtss2si:
     case Intrinsic::x86_sse_cvttss2si64:
     case Intrinsic::x86_sse_cvttss2si:
-      handleVectorConvertIntrinsic(I, 1);
+      handleSSEVectorConvertIntrinsic(I, 1);
       break;
     case Intrinsic::x86_sse_cvtps2pi:
     case Intrinsic::x86_sse_cvttps2pi:
-      handleVectorConvertIntrinsic(I, 2);
+      handleSSEVectorConvertIntrinsic(I, 2);
       break;
 
     case Intrinsic::x86_avx512_psll_w_512:
@@ -4846,6 +4873,27 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
       break;
     }
 
+    // Floating-point Convert to integer, rounding to nearest with ties to Away
+    case Intrinsic::aarch64_neon_fcvtas:
+    case Intrinsic::aarch64_neon_fcvtau:
+    // Floating-point convert to integer, rounding toward minus infinity
+    case Intrinsic::aarch64_neon_fcvtms:
+    case Intrinsic::aarch64_neon_fcvtmu:
+    // Floating-point convert to integer, rounding to nearest with ties to even
+    case Intrinsic::aarch64_neon_fcvtns:
+    case Intrinsic::aarch64_neon_fcvtnu:
+    // Floating-point convert to integer, rounding toward plus infinity
+    case Intrinsic::aarch64_neon_fcvtps:
+    case Intrinsic::aarch64_neon_fcvtpu:
+    // Floating-point Convert to integer, rounding toward Zero
+    case Intrinsic::aarch64_neon_fcvtzs:
+    case Intrinsic::aarch64_neon_fcvtzu:
+    // Floating-point convert to lower precision narrow, rounding to odd
+    case Intrinsic::aarch64_neon_fcvtxn: {
+      handleNEONVectorConvertIntrinsic(I);
+      break;
+    }
+
     case Intrinsic::aarch64_neon_st1x2:
     case Intrinsic::aarch64_neon_st1x3:
     case Intrinsic::aarch64_neon_st1x4: