[OpenCL] Restrict addr space conversions in nested pointers

Address space conversion changes pointer representation.
This commit disallows such conversions when they are not
legal i.e. for the nested pointers even with compatible
address spaces. Because the address space conversion in
the nested levels can't be generated to modify the pointers
correctly. The behavior implemented is as follows:

- Any implicit conversions of nested pointers with different
  address spaces is rejected.
- Any conversion of address spaces in nested pointers in safe
  casts (e.g. const_cast or static_cast) is rejected.
- Conversion in low level C-style or reinterpret_cast is accepted
  but with a warning (this aligns with OpenCL C behavior).

Fixes PR39674

Differential Revision: https://reviews.llvm.org/D73360

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -6760,6 +6760,10 @@ def err_bad_cxx_cast_scalar_to_vector_different_size : Error<
 def err_bad_cxx_cast_vector_to_vector_different_size : Error<
   "%select{||reinterpret_cast||C-style cast|}0 from vector %1 "
   "to vector %2 of different size">;
+def warn_bad_cxx_cast_nested_pointer_addr_space : Warning<
+  "%select{reinterpret_cast|C-style cast}0 from %1 to %2 "
+  "changes address space of nested pointers">,
+  InGroup<IncompatiblePointerTypesDiscardsQualifiers>;
 def err_bad_lvalue_to_rvalue_cast : Error<
   "cannot cast from lvalue of type %1 to rvalue reference type %2; types are "
   "not compatible">;

clang/lib/Sema/SemaCast.cpp

@@ -2311,6 +2311,24 @@ static TryCastResult TryReinterpretCast(Sema &Self, ExprResult &SrcExpr,
     return SuccessResult;
   }
 
+  // Diagnose address space conversion in nested pointers.
+  QualType DestPtee = DestType->getPointeeType().isNull()
+                          ? DestType->getPointeeType()
+                          : DestType->getPointeeType()->getPointeeType();
+  QualType SrcPtee = SrcType->getPointeeType().isNull()
+                         ? SrcType->getPointeeType()
+                         : SrcType->getPointeeType()->getPointeeType();
+  while (!DestPtee.isNull() && !SrcPtee.isNull()) {
+    if (DestPtee.getAddressSpace() != SrcPtee.getAddressSpace()) {
+      Self.Diag(OpRange.getBegin(),
+                diag::warn_bad_cxx_cast_nested_pointer_addr_space)
+          << CStyle << SrcType << DestType << SrcExpr.get()->getSourceRange();
+      break;
+    }
+    DestPtee = DestPtee->getPointeeType();
+    SrcPtee = SrcPtee->getPointeeType();
+  }
+
   // C++ 5.2.10p7: A pointer to an object can be explicitly converted to
   //   a pointer to an object of different type.
   // Void pointers are not specified, but supported by every compiler out there.

clang/lib/Sema/SemaOverload.cpp

@@ -3180,7 +3180,7 @@ static bool isNonTrivialObjCLifetimeConversion(Qualifiers FromQuals,
 /// FromType and \p ToType is permissible, given knowledge about whether every
 /// outer layer is const-qualified.
 static bool isQualificationConversionStep(QualType FromType, QualType ToType,
-                                          bool CStyle,
+                                          bool CStyle, bool IsTopLevel,
                                           bool &PreviousToQualsIncludeConst,
                                           bool &ObjCLifetimeConversion) {
   Qualifiers FromQuals = FromType.getQualifiers();
@@ -3217,11 +3217,15 @@ static bool isQualificationConversionStep(QualType FromType, QualType ToType,
   if (!CStyle && !ToQuals.compatiblyIncludes(FromQuals))
     return false;
 
-  // For a C-style cast, just require the address spaces to overlap.
-  // FIXME: Does "superset" also imply the representation of a pointer is the
-  // same? We're assuming that it does here and in compatiblyIncludes.
-  if (CStyle && !ToQuals.isAddressSpaceSupersetOf(FromQuals) &&
-      !FromQuals.isAddressSpaceSupersetOf(ToQuals))
+  // If address spaces mismatch:
+  //  - in top level it is only valid to convert to addr space that is a
+  //    superset in all cases apart from C-style casts where we allow
+  //    conversions between overlapping address spaces.
+  //  - in non-top levels it is not a valid conversion.
+  if (ToQuals.getAddressSpace() != FromQuals.getAddressSpace() &&
+      (!IsTopLevel ||
+       !(ToQuals.isAddressSpaceSupersetOf(FromQuals) ||
+         (CStyle && FromQuals.isAddressSpaceSupersetOf(ToQuals)))))
     return false;
 
   //   -- if the cv 1,j and cv 2,j are different, then const is in
@@ -3262,9 +3266,9 @@ Sema::IsQualificationConversion(QualType FromType, QualType ToType,
   bool PreviousToQualsIncludeConst = true;
   bool UnwrappedAnyPointer = false;
   while (Context.UnwrapSimilarTypes(FromType, ToType)) {
-    if (!isQualificationConversionStep(FromType, ToType, CStyle,
-                                       PreviousToQualsIncludeConst,
-                                       ObjCLifetimeConversion))
+    if (!isQualificationConversionStep(
+            FromType, ToType, CStyle, !UnwrappedAnyPointer,
+            PreviousToQualsIncludeConst, ObjCLifetimeConversion))
       return false;
     UnwrappedAnyPointer = true;
   }
@@ -4508,7 +4512,7 @@ Sema::CompareReferenceRelationship(SourceLocation Loc,
     // If we find a qualifier mismatch, the types are not reference-compatible,
     // but are still be reference-related if they're similar.
     bool ObjCLifetimeConversion = false;
-    if (!isQualificationConversionStep(T2, T1, /*CStyle=*/false,
+    if (!isQualificationConversionStep(T2, T1, /*CStyle=*/false, TopLevel,
                                        PreviousToQualsIncludeConst,
                                        ObjCLifetimeConversion))
       return (ConvertedReferent || Context.hasSimilarType(T1, T2))

clang/test/SemaOpenCL/address-spaces-conversions-cl2.0.cl

@@ -513,17 +513,37 @@ void test_pointer_chains() {
 #endif
 
   // Case 3: Corresponded inner pointees has overlapping but not equivalent address spaces.
-  // FIXME: Should this really be allowed in C++ mode?
   var_as_as_int = var_asc_asc_int;
-#if !__OPENCL_CPP_VERSION__
 #ifdef GENERIC
+#if !__OPENCL_CPP_VERSION__
 // expected-error@-3 {{assigning '__local int *__local *__private' to '__generic int *__generic *__private' changes address space of nested pointer}}
+#else
+// expected-error@-5 {{assigning to '__generic int *__generic *' from incompatible type '__local int *__local *__private'}}
 #endif
 #endif
-  var_as_as_int = 0 ? var_as_as_int : var_asc_asc_int;
-#if !__OPENCL_CPP_VERSION__
+
+  var_as_as_int = (AS int *AS *)var_asc_asc_int;
 #ifdef GENERIC
+#if !__OPENCL_CPP_VERSION__
+// expected-warning@-3 {{casting '__local int *__local *' to type '__generic int *__generic *' discards qualifiers in nested pointer types}}
+#else
+// expected-warning@-5 {{C-style cast from '__local int *__local *' to '__generic int *__generic *' changes address space of nested pointers}}
+#endif
+#endif
+
+  var_as_as_int = (AS int *AS *)var_asc_asn_int;
+#if !__OPENCL_CPP_VERSION__
+// expected-warning-re@-2 {{casting '__{{global|local|constant}} int *__{{local|constant|global}} *' to type '__{{global|constant|generic}} int *__{{global|constant|generic}} *' discards qualifiers in nested pointer types}}
+#else
+// expected-warning-re@-4 {{C-style cast from '__{{global|local|constant}} int *__{{local|constant|global}} *' to '__{{global|constant|generic}} int *__{{global|constant|generic}} *' changes address space of nested pointers}}
+#endif
+
+  var_as_as_int = 0 ? var_as_as_int : var_asc_asc_int;
+#ifdef GENERIC
+#if !__OPENCL_CPP_VERSION__
 // expected-warning@-3{{pointer type mismatch ('__generic int *__generic *' and '__local int *__local *')}}
+#else
+// expected-error@-5 {{incompatible operand types ('__generic int *__generic *' and '__local int *__local *')}}
 #endif
 #endif
 }

clang/test/SemaOpenCL/address-spaces.cl

@@ -198,9 +198,7 @@ void nested(__global int *g, __global int * __private *gg, __local int *l, __loc
   ll = gg;   // expected-error {{assigning to '__local int *__private *' from incompatible type '__global int *__private *__private'}}
   ll = l;    // expected-error {{assigning to '__local int *__private *' from incompatible type '__local int *__private'; take the address with &}}
   ll = gg_f; // expected-error {{assigning to '__local int *__private *' from incompatible type '__global float *__private *__private'}}
-  // FIXME: The below becomes a reinterpret_cast, and therefore does not emit an error
-  // even though the address space mismatches in the nested pointers.
-  ll = (__local int * __private *)gg;
+  ll = (__local int *__private *)gg; //expected-warning{{C-style cast from '__global int *__private *' to '__local int *__private *' changes address space of nested pointers}}
 
   gg_f = g;  // expected-error {{assigning to '__global float *__private *' from incompatible type '__global int *__private'}}
   gg_f = gg; // expected-error {{assigning to '__global float *__private *' from incompatible type '__global int *__private *__private'}}

clang/test/SemaOpenCLCXX/address-space-castoperators.cl

@@ -0,0 +1,12 @@
+//RUN: %clang_cc1 %s -cl-std=clc++ -pedantic -ast-dump -verify | FileCheck %s
+
+void nester_ptr() {
+  local int * * locgen;
+  constant int * * congen;
+  int * * gengen;
+
+  gengen = const_cast<int**>(locgen); //expected-error{{const_cast from '__local int *__generic *' to '__generic int *__generic *' is not allowed}}
+  gengen = static_cast<int**>(locgen); //expected-error{{static_cast from '__local int *__generic *' to '__generic int *__generic *' is not allowed}}
+// CHECK-NOT: AddressSpaceConversion
+  gengen = reinterpret_cast<int**>(locgen); //expected-warning{{reinterpret_cast from '__local int *__generic *' to '__generic int *__generic *' changes address space of nested pointers}}
+}

clang/test/SemaOpenCLCXX/address-space-deduction.cl

@@ -105,7 +105,7 @@ void t5(float (*(*fYZ))[2]);
 
 __kernel void k() {
   __local float x[2];
-  __local float(*p)[2];
+  float(*p)[2];
   t1(x);
   t2(&x);
   t3(&x);

clang/test/SemaOpenCLCXX/address-space-references.cl

@@ -13,3 +13,16 @@ int bar(const unsigned int &i);
 void foo() {
   bar(1) // expected-error{{binding reference of type 'const __global unsigned int' to value of type 'int' changes address space}}
 }
+
+// Test addr space conversion with nested pointers
+
+extern void nestptr(int *&); // expected-note {{candidate function not viable: no known conversion from '__global int *__private' to '__generic int *__generic &__private' for 1st argument}}
+extern void nestptr_const(int * const &); // expected-note {{candidate function not viable: cannot pass pointer to address space '__constant' as a pointer to address space '__generic' in 1st argument}}
+int test_nestptr(__global int *glob, __constant int *cons, int* gen) {
+  nestptr(glob); // expected-error{{no matching function for call to 'nestptr'}}
+  // Addr space conversion first occurs on a temporary.
+  nestptr_const(glob);
+  // No legal conversion between disjoint addr spaces.
+  nestptr_const(cons); // expected-error{{no matching function for call to 'nestptr_const'}}
+  return *(*cons ? glob : gen);
+}