[clang][Interp] Implement VectorSplat casts

Author: tbaederr

clang/lib/AST/Interp/ByteCodeExprGen.cpp

@@ -398,6 +398,35 @@ bool ByteCodeExprGen<Emitter>::VisitCastExpr(const CastExpr *CE) {
     return true;
   }
 
+  case CK_VectorSplat: {
+    assert(!classify(CE->getType()));
+    assert(classify(SubExpr->getType()));
+    assert(CE->getType()->isVectorType());
+
+    if (DiscardResult)
+      return this->discard(SubExpr);
+
+    assert(Initializing); // FIXME: Not always correct.
+    const auto *VT = CE->getType()->getAs<VectorType>();
+    PrimType ElemT = classifyPrim(SubExpr);
+    unsigned ElemOffset = allocateLocalPrimitive(
+        SubExpr, ElemT, /*IsConst=*/true, /*IsExtended=*/false);
+
+    if (!this->visit(SubExpr))
+      return false;
+    if (!this->emitSetLocal(ElemT, ElemOffset, CE))
+      return false;
+
+    for (unsigned I = 0; I != VT->getNumElements(); ++I) {
+      if (!this->emitGetLocal(ElemT, ElemOffset, CE))
+        return false;
+      if (!this->emitInitElem(ElemT, I, CE))
+        return false;
+    }
+
+    return true;
+  }
+
   case CK_ToVoid:
     return discard(SubExpr);
 

clang/lib/AST/Interp/ByteCodeExprGen.h

@@ -148,13 +148,20 @@ class ByteCodeExprGen : public ConstStmtVisitor<ByteCodeExprGen<Emitter>, bool>,
     return Ctx.classify(Ty);
   }
 
-  /// Classifies a known primitive type
+  /// Classifies a known primitive type.
   PrimType classifyPrim(QualType Ty) const {
     if (auto T = classify(Ty)) {
       return *T;
     }
     llvm_unreachable("not a primitive type");
   }
+  /// Classifies a known primitive expression.
+  PrimType classifyPrim(const Expr *E) const {
+    if (auto T = classify(E))
+      return *T;
+    llvm_unreachable("not a primitive type");
+  }
+
   /// Evaluates an expression and places the result on the stack. If the
   /// expression is of composite type, a local variable will be created
   /// and a pointer to said variable will be placed on the stack.

clang/test/AST/Interp/vectors.cpp

@@ -1,10 +1,23 @@
 // RUN: %clang_cc1 -fexperimental-new-constant-interpreter -verify=expected,both %s
 // RUN: %clang_cc1 -verify=ref,both %s
 
-// ref-no-diagnostics
-
 typedef int __attribute__((vector_size(16))) VI4;
 constexpr VI4 A = {1,2,3,4};
+static_assert(A[0] == 1, ""); // ref-error {{not an integral constant expression}}
+static_assert(A[1] == 2, ""); // ref-error {{not an integral constant expression}}
+static_assert(A[2] == 3, ""); // ref-error {{not an integral constant expression}}
+static_assert(A[3] == 4, ""); // ref-error {{not an integral constant expression}}
+
+/// VectorSplat casts
+typedef __attribute__(( ext_vector_type(4) )) float float4;
+constexpr float4 vec4_0 = (float4)0.5f;
+static_assert(vec4_0[0] == 0.5, ""); // ref-error {{not an integral constant expression}}
+static_assert(vec4_0[1] == 0.5, ""); // ref-error {{not an integral constant expression}}
+static_assert(vec4_0[2] == 0.5, ""); // ref-error {{not an integral constant expression}}
+static_assert(vec4_0[3] == 0.5, ""); // ref-error {{not an integral constant expression}}
+constexpr int vec4_0_discarded = ((float4)12.0f, 0);
+
+
 
 /// From constant-expression-cxx11.cpp
 namespace Vector {