[llvm] [msan] Handle llvm.x86.vcvtps2ph.128/256 explicitly (PR #130705)

[Florian Mayer via llvm-commits]

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@@ -3273,6 +3273,66 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
     setOriginForNaryOp(I);
   }
 
+  /// Handle x86 SSE single-precision to half-precision conversion.
+  ///
+  /// e.g.,
+  ///      <8 x i16> @llvm.x86.vcvtps2ph.256(<8 x float> %a0, i32 0)
+  ///      <8 x i16> @llvm.x86.vcvtps2ph.128(<4 x float> %a0, i32 0)
+  /// Note: if the output has more elements, they are zero-initialized (and
+  /// therefore the shadow will also be initialized).
+  ///
+  /// This differs from handleSSEVectorConvertIntrinsic() because it
+  /// propagates uninitialized shadow (instead of checking the shadow).
+  void handleSSEVectorConvertIntrinsicByProp(IntrinsicInst &I) {
+    assert(I.arg_size() == 2);
+    Value *Src = I.getArgOperand(0);
+    assert(Src->getType()->isVectorTy());
+    [[maybe_unused]] Value *RoundingMode = I.getArgOperand(1);
+    assert(RoundingMode->getType()->isIntegerTy());
+
+    // The return type might have more elements than the input.
+    // Temporarily shrink the return type's number of elements.
+    VectorType *ShadowType = cast<VectorType>(getShadowTy(&I));
+    if (ShadowType->getElementCount() ==
+        cast<VectorType>(Src->getType())->getElementCount() * 2)
+      ShadowType = VectorType::getHalfElementsVectorType(ShadowType);
+
+    assert(ShadowType->getElementCount() ==
+           cast<VectorType>(Src->getType())->getElementCount());
+
+    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 *Shadow =
+        IRB.CreateSExt(IRB.CreateICmpNE(S0, getCleanShadow(S0)), ShadowType);
+
+    // The return type might have more elements than the input.
+    // Extend the return type back to its original width if necessary.
+    Value *FullShadow = getCleanShadow(&I);
+
+    if (Shadow->getType() == FullShadow->getType())
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fmayer wrote:

Add `{}` to avoid mixed if/else

https://github.com/llvm/llvm-project/pull/130705