[HLSL] error on out of bounds vector accesses

clang/docs/ReleaseNotes.rst

@@ -230,6 +230,8 @@ Improvements to Clang's diagnostics
   under the subgroup ``-Wunsafe-buffer-usage-in-libc-call``.
 - Diagnostics on chained comparisons (``a < b < c``) are now an error by default. This can be disabled with
   ``-Wno-error=parentheses``.
+- Adds an error diagnostic for out of bounds vector accesses; produces an error
+  for compile time statically provable out of bounds vector accesses.
 - The ``-Wshift-bool`` warning has been added to warn about shifting a boolean. (#GH28334)
 - Fixed diagnostics adding a trailing ``::`` when printing some source code
   constructs, like base classes.

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -10684,6 +10684,9 @@ def err_block_on_vm : Error<
 def err_sizeless_nonlocal : Error<
   "non-local variable with sizeless type %0">;
 
+def err_vector_index_out_of_range : Error<
+  "vector element index %0 is out of bounds">;
+
 def err_vec_builtin_non_vector : Error<
  "%select{first two|all}1 arguments to %0 must be vectors">;
 def err_vec_builtin_incompatible_vector : Error<

clang/include/clang/Sema/Sema.h

@@ -2468,6 +2468,7 @@ class Sema final : public SemaBase {
                         const ArraySubscriptExpr *ASE = nullptr,
                         bool AllowOnePastEnd = true, bool IndexNegated = false);
   void CheckArrayAccess(const Expr *E);
+  void CheckVectorAccess(const Expr *BaseExpr, const Expr *IndexExpr);
 
   bool CheckPointerCall(NamedDecl *NDecl, CallExpr *TheCall,
                         const FunctionProtoType *Proto);

clang/lib/Sema/SemaChecking.cpp

@@ -14054,6 +14054,23 @@ void Sema::CheckCastAlign(Expr *Op, QualType T, SourceRange TRange) {
     << TRange << Op->getSourceRange();
 }
 
+void Sema::CheckVectorAccess(const Expr *BaseExpr, const Expr *IndexExpr) {
+  const auto *VTy = BaseExpr->getType()->getAs<VectorType>();
+  if (!VTy)
+    return;
+
+  Expr::EvalResult Result;
+  if (!IndexExpr->EvaluateAsInt(Result, Context, Expr::SE_AllowSideEffects))
+    return;
+
+  unsigned DiagID = diag::err_vector_index_out_of_range;
+
+  llvm::APSInt index = Result.Val.getInt();
+  if (index.isNegative() || index >= VTy->getNumElements())
+    Diag(BaseExpr->getBeginLoc(), DiagID) << toString(index, 10, true);
+  return;
+}
+
 void Sema::CheckArrayAccess(const Expr *BaseExpr, const Expr *IndexExpr,
                             const ArraySubscriptExpr *ASE,
                             bool AllowOnePastEnd, bool IndexNegated) {
@@ -14068,6 +14085,12 @@ void Sema::CheckArrayAccess(const Expr *BaseExpr, const Expr *IndexExpr,
   const Type *EffectiveType =
       BaseExpr->getType()->getPointeeOrArrayElementType();
   BaseExpr = BaseExpr->IgnoreParenCasts();
+
+  if (BaseExpr->getType()->isVectorType()) {
+    CheckVectorAccess(BaseExpr, IndexExpr);
+    return;
+  }
+
   const ConstantArrayType *ArrayTy =
       Context.getAsConstantArrayType(BaseExpr->getType());
 

clang/test/CodeGenCXX/x86_64-arguments.cpp

@@ -215,6 +215,6 @@ union U {
   float f1;
   char __attribute__((__vector_size__(1))) f2;
 };
-int f(union U u) { return u.f2[1]; }
+int f(union U u) { return u.f2[0]; }
 // CHECK-LABEL: define{{.*}} i32 @_ZN6test111fENS_1UE(i32
 }

clang/test/SemaHLSL/Language/VectorOutOfRange-errors.hlsl

@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -finclude-default-header -triple dxil-pc-shadermodel6.6-library %s -verify
+
+export void fn1() {
+  int2 A = {1,2};
+  int X = A[-1];
+  // expected-error@-1 {{vector element index -1 is out of bounds}}
+}
+
+export void fn2() {
+  int4 A = {1,2,3,4};
+  int X = A[4];
+  // expected-error@-1 {{vector element index 4 is out of bounds}}
+}
+
+export void fn3() {
+  bool2 A = {true,true};
+  bool X = A[-1];
+  // expected-error@-1 {{vector element index -1 is out of bounds}}
+}