[clang][ExprConst] Reject unary vector shuffles

clang/docs/ReleaseNotes.rst

@@ -288,6 +288,10 @@ Improvements to Clang's diagnostics
 - Fixed a bug where the source location was missing when diagnosing ill-formed
   placeholder constraints.
 
+- The two-element, unary mask variant of ``__builtin_shufflevector`` is now
+  properly being rejected when used at compile-time. It was not implemented
+  and caused assertion failures before (#GH158471).
+
 Improvements to Clang's time-trace
 ----------------------------------
 

clang/lib/AST/ByteCode/Compiler.cpp

@@ -3986,6 +3986,10 @@ bool Compiler<Emitter>::VisitConvertVectorExpr(const ConvertVectorExpr *E) {
 
 template <class Emitter>
 bool Compiler<Emitter>::VisitShuffleVectorExpr(const ShuffleVectorExpr *E) {
+  // FIXME: Unary shuffle with mask not currently supported.
+  if (E->getNumSubExprs() == 2)
+    return this->emitInvalid(E);
+
   assert(Initializing);
   assert(E->getNumSubExprs() > 2);
 

clang/lib/AST/ExprConstant.cpp

@@ -12160,6 +12160,9 @@ static bool handleVectorShuffle(EvalInfo &Info, const ShuffleVectorExpr *E,
 }
 
 bool VectorExprEvaluator::VisitShuffleVectorExpr(const ShuffleVectorExpr *E) {
+  // FIXME: Unary shuffle with mask not currently supported.
+  if (E->getNumSubExprs() == 2)
+    return Error(E);
   APValue VecVal1;
   const Expr *Vec1 = E->getExpr(0);
   if (!EvaluateAsRValue(Info, Vec1, VecVal1))

clang/lib/Sema/SemaChecking.cpp

@@ -5558,17 +5558,18 @@ bool Sema::BuiltinComplex(CallExpr *TheCall) {
 /// BuiltinShuffleVector - Handle __builtin_shufflevector.
 // This is declared to take (...), so we have to check everything.
 ExprResult Sema::BuiltinShuffleVector(CallExpr *TheCall) {
-  if (TheCall->getNumArgs() < 2)
+  unsigned NumArgs = TheCall->getNumArgs();
+  if (NumArgs < 2)
     return ExprError(Diag(TheCall->getEndLoc(),
                           diag::err_typecheck_call_too_few_args_at_least)
-                     << 0 /*function call*/ << 2 << TheCall->getNumArgs()
+                     << 0 /*function call*/ << 2 << NumArgs
                      << /*is non object*/ 0 << TheCall->getSourceRange());
 
   // Determine which of the following types of shufflevector we're checking:
   // 1) unary, vector mask: (lhs, mask)
   // 2) binary, scalar mask: (lhs, rhs, index, ..., index)
-  QualType resType = TheCall->getArg(0)->getType();
-  unsigned numElements = 0;
+  QualType ResType = TheCall->getArg(0)->getType();
+  unsigned NumElements = 0;
 
   if (!TheCall->getArg(0)->isTypeDependent() &&
       !TheCall->getArg(1)->isTypeDependent()) {
@@ -5578,43 +5579,43 @@ ExprResult Sema::BuiltinShuffleVector(CallExpr *TheCall) {
     if (!LHSType->isVectorType() || !RHSType->isVectorType())
       return ExprError(
           Diag(TheCall->getBeginLoc(), diag::err_vec_builtin_non_vector)
-          << TheCall->getDirectCallee() << /*isMorethantwoArgs*/ false
+          << TheCall->getDirectCallee() << /*isMoreThanTwoArgs*/ false
           << SourceRange(TheCall->getArg(0)->getBeginLoc(),
                          TheCall->getArg(1)->getEndLoc()));
 
-    numElements = LHSType->castAs<VectorType>()->getNumElements();
-    unsigned numResElements = TheCall->getNumArgs() - 2;
+    NumElements = LHSType->castAs<VectorType>()->getNumElements();
+    unsigned NumResElements = NumArgs - 2;
 
     // Check to see if we have a call with 2 vector arguments, the unary shuffle
     // with mask.  If so, verify that RHS is an integer vector type with the
     // same number of elts as lhs.
-    if (TheCall->getNumArgs() == 2) {
+    if (NumArgs == 2) {
       if (!RHSType->hasIntegerRepresentation() ||
-          RHSType->castAs<VectorType>()->getNumElements() != numElements)
+          RHSType->castAs<VectorType>()->getNumElements() != NumElements)
         return ExprError(Diag(TheCall->getBeginLoc(),
                               diag::err_vec_builtin_incompatible_vector)
                          << TheCall->getDirectCallee()
-                         << /*isMorethantwoArgs*/ false
+                         << /*isMoreThanTwoArgs*/ false
                          << SourceRange(TheCall->getArg(1)->getBeginLoc(),
                                         TheCall->getArg(1)->getEndLoc()));
     } else if (!Context.hasSameUnqualifiedType(LHSType, RHSType)) {
       return ExprError(Diag(TheCall->getBeginLoc(),
                             diag::err_vec_builtin_incompatible_vector)
                        << TheCall->getDirectCallee()
-                       << /*isMorethantwoArgs*/ false
+                       << /*isMoreThanTwoArgs*/ false
                        << SourceRange(TheCall->getArg(0)->getBeginLoc(),
                                       TheCall->getArg(1)->getEndLoc()));
-    } else if (numElements != numResElements) {
-      QualType eltType = LHSType->castAs<VectorType>()->getElementType();
-      resType = resType->isExtVectorType()
-                    ? Context.getExtVectorType(eltType, numResElements)
-                    : Context.getVectorType(eltType, numResElements,
+    } else if (NumElements != NumResElements) {
+      QualType EltType = LHSType->castAs<VectorType>()->getElementType();
+      ResType = ResType->isExtVectorType()
+                    ? Context.getExtVectorType(EltType, NumResElements)
+                    : Context.getVectorType(EltType, NumResElements,
                                             VectorKind::Generic);
     }
   }
 
-  for (unsigned i = 2; i < TheCall->getNumArgs(); i++) {
-    Expr *Arg = TheCall->getArg(i);
+  for (unsigned I = 2; I != NumArgs; ++I) {
+    Expr *Arg = TheCall->getArg(I);
     if (Arg->isTypeDependent() || Arg->isValueDependent())
       continue;
 
@@ -5628,23 +5629,21 @@ ExprResult Sema::BuiltinShuffleVector(CallExpr *TheCall) {
     if (Result->isSigned() && Result->isAllOnes())
       ;
     else if (Result->getActiveBits() > 64 ||
-             Result->getZExtValue() >= numElements * 2)
+             Result->getZExtValue() >= NumElements * 2)
       return ExprError(Diag(TheCall->getBeginLoc(),
                             diag::err_shufflevector_argument_too_large)
                        << Arg->getSourceRange());
 
-    TheCall->setArg(i, ConstantExpr::Create(Context, Arg, APValue(*Result)));
+    TheCall->setArg(I, ConstantExpr::Create(Context, Arg, APValue(*Result)));
   }
 
-  SmallVector<Expr *> exprs;
-  for (unsigned i = 0, e = TheCall->getNumArgs(); i != e; i++) {
-    exprs.push_back(TheCall->getArg(i));
-    TheCall->setArg(i, nullptr);
-  }
+  auto *Result = new (Context) ShuffleVectorExpr(
+      Context, ArrayRef(TheCall->getArgs(), NumArgs), ResType,
+      TheCall->getCallee()->getBeginLoc(), TheCall->getRParenLoc());
 
-  return new (Context) ShuffleVectorExpr(Context, exprs, resType,
-                                         TheCall->getCallee()->getBeginLoc(),
-                                         TheCall->getRParenLoc());
+  // All moved to Result.
+  TheCall->shrinkNumArgs(0);
+  return Result;
 }
 
 ExprResult Sema::ConvertVectorExpr(Expr *E, TypeSourceInfo *TInfo,

clang/test/Sema/constant-builtins-vector.cpp

@@ -731,6 +731,19 @@ permitted in a constexpr context}}
         vector4charConst1,
         vector4charConst2, -1, -1, -1, -1);
 
+namespace UnaryShuffleUnsupported {
+  typedef int vi6 __attribute__((ext_vector_type(2)));
+  constexpr int foo() { // expected-error {{never produces a constant expression}}
+    vi6 a = {1,2};
+    vi6 b = {3,4};
+    vi6 r = __builtin_shufflevector(a, b); // expected-note 2{{subexpression not valid in a constant expression}}
+
+    return r[0] + r[1];
+  }
+  static_assert(foo() == 0); // expected-error {{not an integral constant expression}} \
+                             // expected-note {{in call to}}
+}
+
 static_assert(__builtin_reduce_add((vector4char){}) == 0);
 static_assert(__builtin_reduce_add((vector4char){1, 2, 3, 4}) == 10);
 static_assert(__builtin_reduce_add((vector4short){10, 20, 30, 40}) == 100);