1 files changed, 35 insertions, 4 deletions
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index a488c80979f..d9d619e802b 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -1014,10 +1014,41 @@ Value *ScalarExprEmitter::EmitScalarConversion(Value *Src, QualType SrcType,
     return Builder.CreateVectorSplat(NumElements, Src, "splat");
   }
 
-  // Allow bitcast from vector to integer/fp of the same size.
-  if (isa<llvm::VectorType>(SrcTy) ||
-      isa<llvm::VectorType>(DstTy))
-    return Builder.CreateBitCast(Src, DstTy, "conv");
+  if (isa<llvm::VectorType>(SrcTy) || isa<llvm::VectorType>(DstTy)) {
+    // Allow bitcast from vector to integer/fp of the same size.
+    unsigned SrcSize = SrcTy->getPrimitiveSizeInBits();
+    unsigned DstSize = DstTy->getPrimitiveSizeInBits();
+    if (SrcSize == DstSize)
+      return Builder.CreateBitCast(Src, DstTy, "conv");
+
+    // Conversions between vectors of different sizes are not allowed except
+    // when vectors of half are involved. Operations on storage-only half
+    // vectors require promoting half vector operands to float vectors and
+    // truncating the result, which is either an int or float vector, to a
+    // short or half vector.
+
+    // Source and destination are both expected to be vectors.
+    llvm::Type *SrcElementTy = SrcTy->getVectorElementType();
+    llvm::Type *DstElementTy = DstTy->getVectorElementType();
+
+    assert(((SrcElementTy->isIntegerTy() &&
+             DstElementTy->isIntegerTy()) ||
+            (SrcElementTy->isFloatingPointTy() &&
+             DstElementTy->isFloatingPointTy())) &&
+           "unexpected conversion between a floating-point vector and an "
+           "integer vector");
+
+    // Truncate an i32 vector to an i16 vector.
+    if (SrcElementTy->isIntegerTy())
+      return Builder.CreateIntCast(Src, DstTy, false, "conv");
+
+    // Truncate a float vector to a half vector.
+    if (SrcSize > DstSize)
+      return Builder.CreateFPTrunc(Src, DstTy, "conv");
+
+    // Promote a half vector to a float vector.
+    return Builder.CreateFPExt(Src, DstTy, "conv");
+  }
 
   // Finally, we have the arithmetic types: real int/float.
   Value *Res = nullptr;