[clang][bytecode] Check vector element types for eligibility (#119385)

Like we do in ExprConstant.cpp.

clang/lib/AST/ByteCode/InterpBuiltinBitCast.cpp

@@ -222,6 +222,35 @@ static bool CheckBitcastType(InterpState &S, CodePtr OpPC, QualType T,
                         IsToType))
     return false;
 
+  if (const auto *VT = T->getAs<VectorType>()) {
+    const ASTContext &ASTCtx = S.getASTContext();
+    QualType EltTy = VT->getElementType();
+    unsigned NElts = VT->getNumElements();
+    unsigned EltSize =
+        VT->isExtVectorBoolType() ? 1 : ASTCtx.getTypeSize(EltTy);
+
+    if ((NElts * EltSize) % ASTCtx.getCharWidth() != 0) {
+      // The vector's size in bits is not a multiple of the target's byte size,
+      // so its layout is unspecified. For now, we'll simply treat these cases
+      // as unsupported (this should only be possible with OpenCL bool vectors
+      // whose element count isn't a multiple of the byte size).
+      const Expr *E = S.Current->getExpr(OpPC);
+      S.FFDiag(E, diag::note_constexpr_bit_cast_invalid_vector)
+          << QualType(VT, 0) << EltSize << NElts << ASTCtx.getCharWidth();
+      return false;
+    }
+
+    if (EltTy->isRealFloatingType() &&
+        &ASTCtx.getFloatTypeSemantics(EltTy) == &APFloat::x87DoubleExtended()) {
+      // The layout for x86_fp80 vectors seems to be handled very inconsistently
+      // by both clang and LLVM, so for now we won't allow bit_casts involving
+      // it in a constexpr context.
+      const Expr *E = S.Current->getExpr(OpPC);
+      S.FFDiag(E, diag::note_constexpr_bit_cast_unsupported_type) << EltTy;
+      return false;
+    }
+  }
+
   return true;
 }
 

clang/test/AST/ByteCode/builtin-bit-cast.cpp

@@ -502,3 +502,8 @@ namespace OversizedBitField {
                                                                                  // ref-note {{constexpr bit_cast involving bit-field is not yet supported}}
 #endif
 }
+
+typedef bool bool9 __attribute__((ext_vector_type(9)));
+// both-error@+2 {{constexpr variable 'bad_bool9_to_short' must be initialized by a constant expression}}
+// both-note@+1 {{bit_cast involving type 'bool __attribute__((ext_vector_type(9)))' (vector of 9 'bool' values) is not allowed in a constant expression; element size 1 * element count 9 is not a multiple of the byte size 8}}
+constexpr unsigned short bad_bool9_to_short = __builtin_bit_cast(unsigned short, bool9{1,1,0,1,0,1,0,1,0});