r337540 - Sema: Fix explicit address space cast in C++
Liu, Yaxun (Sam) via cfe-commits
cfe-commits at lists.llvm.org
Fri Jul 20 14:20:18 PDT 2018
From: Richard Smith [mailto:richard at metafoo.co.uk]
Sent: Friday, July 20, 2018 3:29 PM
To: Liu, Yaxun (Sam) <Yaxun.Liu at amd.com>
Cc: cfe-commits <cfe-commits at lists.llvm.org>
Subject: Re: r337540 - Sema: Fix explicit address space cast in C++
On Fri, 20 Jul 2018 at 12:00, Richard Smith <richard at metafoo.co.uk<mailto:richard at metafoo.co.uk>> wrote:
On Fri, 20 Jul 2018 at 04:38, Yaxun Liu via cfe-commits <cfe-commits at lists.llvm.org<mailto:cfe-commits at lists.llvm.org>> wrote:
Author: yaxunl
Date: Fri Jul 20 04:32:51 2018
New Revision: 337540
URL: http://llvm.org/viewvc/llvm-project?rev=337540&view=rev
Log:
Sema: Fix explicit address space cast in C++
Currently clang does not allow implicit cast of a pointer to a pointer type
in different address space but allows C-style cast of a pointer to a pointer
type in different address space. However, there is a bug in Sema causing
incorrect Cast Expr in AST for the latter case, which in turn results in
invalid LLVM IR in codegen.
This is because Sema::IsQualificationConversion returns true for a cast of
pointer to a pointer type in different address space, which in turn allows
a standard conversion and results in a cast expression with no op in AST.
This patch fixes that by let Sema::IsQualificationConversion returns false
for a cast of pointer to a pointer type in different address space, which
in turn disallows standard conversion, implicit cast, and static cast.
Finally it results in an reinterpret cast and correct conversion kind is set.
Differential Revision: https://reviews.llvm.org/D49294
Added:
cfe/trunk/test/CodeGenCXX/address-space-cast.cpp
Modified:
cfe/trunk/lib/Sema/SemaCast.cpp
cfe/trunk/lib/Sema/SemaOverload.cpp
Modified: cfe/trunk/lib/Sema/SemaCast.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaCast.cpp?rev=337540&r1=337539&r2=337540&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaCast.cpp (original)
+++ cfe/trunk/lib/Sema/SemaCast.cpp Fri Jul 20 04:32:51 2018
@@ -1955,6 +1955,12 @@ static bool fixOverloadedReinterpretCast
return Result.isUsable();
}
+static bool IsAddressSpaceConversion(QualType SrcType, QualType DestType) {
+ return SrcType->isPointerType() && DestType->isPointerType() &&
+ SrcType->getAs<PointerType>()->getPointeeType().getAddressSpace() !=
+ DestType->getAs<PointerType>()->getPointeeType().getAddressSpace();
+}
+
static TryCastResult TryReinterpretCast(Sema &Self, ExprResult &SrcExpr,
QualType DestType, bool CStyle,
SourceRange OpRange,
@@ -2198,6 +2204,8 @@ static TryCastResult TryReinterpretCast(
} else {
Kind = CK_BitCast;
}
+ } else if (IsAddressSpaceConversion(SrcType, DestType)) {
+ Kind = CK_AddressSpaceConversion;
This seems wrong to me. A reinterpret_cast from a pointer to one address space into a pointer to a different address space should be a bit cast, not an address space conversion.
Hmm. I suppose we have a choice: either reinterpret_cast always means 'reinterpret these bits as this other type' (and there are C-style casts that cannot be expressed in terms of named casts, violating the usual C++ rules for C-style casts) or reinterpret_cast between pointers always gives you a pointer to the same byte of storage and an address space bitcast requires casting via an integral type (violating the normal behavior that reinterpret_cast reinterprets the representation and doesn't change the value). These options both seem unsatisfying, but what you have here (reinterpret_cast attempts to form a pointer to the same byte) is definitely the more useful of those two options.
Do any of our supported language extensions actually say what named casts in C++ do when attempting to cast between address spaces? The OpenCL 2.2 C++ extensions specification doesn't add address space qualifiers, so it doesn't have an answer for us.
[Sam] I don’t know C++ based languages having rules about pointers casting to a different address space. OpenCL C’s rules about C-style cast of pointers to a different address space clearly means pointing to the same memory location. Bitwise cast isn’t useful in most use cases. Since there is no language rule in C++ for casting a pointer to a different address space, the C-style cast cannot be treated as a static cast in C++ since it mostly involves transformations, then it is more suitably treated as a reinterpret cast. If users do need bitwise cast, they can go through some integer, as you suggested.
} else {
Kind = CK_BitCast;
}
Modified: cfe/trunk/lib/Sema/SemaOverload.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaOverload.cpp?rev=337540&r1=337539&r2=337540&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaOverload.cpp (original)
+++ cfe/trunk/lib/Sema/SemaOverload.cpp Fri Jul 20 04:32:51 2018
@@ -3150,6 +3150,15 @@ Sema::IsQualificationConversion(QualType
= PreviousToQualsIncludeConst && ToQuals.hasConst();
}
+ // Allows address space promotion by language rules implemented in
+ // Type::Qualifiers::isAddressSpaceSupersetOf.
+ Qualifiers FromQuals = FromType.getQualifiers();
+ Qualifiers ToQuals = ToType.getQualifiers();
+ if (!ToQuals.isAddressSpaceSupersetOf(FromQuals) &&
+ !FromQuals.isAddressSpaceSupersetOf(ToQuals)) {
Is this right? Qualification conversions are usually only permitted for "guaranteed-safe" conversions, which would be cases where the target address space is a superset of the source address space only. And OpenCL 2.2's C extensions specification (section 1.5.6, changes to 6.3.2.3) says:
"For any qualifier q, a pointer to a non-q-qualified type may be converted to a pointer to the q-qualified version of the type (but with the same address-space qualifier or the generic address space); the values stored in the original and converted pointers shall compare equal."
... which looks to me like OpenCL only permits going from subset to superset address space in C's equivalent to a qualification conversion. I don't think we want to support:
char *p;
__private__ char *q = p;
(with no cast) in C++.
+ return false;
+ }
+
// We are left with FromType and ToType being the pointee types
// after unwrapping the original FromType and ToType the same number
// of types. If we unwrapped any pointers, and if FromType and
Added: cfe/trunk/test/CodeGenCXX/address-space-cast.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/address-space-cast.cpp?rev=337540&view=auto
==============================================================================
--- cfe/trunk/test/CodeGenCXX/address-space-cast.cpp (added)
+++ cfe/trunk/test/CodeGenCXX/address-space-cast.cpp Fri Jul 20 04:32:51 2018
@@ -0,0 +1,15 @@
+// RUN: %clang_cc1 %s -triple=amdgcn-amd-amdhsa -emit-llvm -o - | FileCheck %s
+
+#define __private__ __attribute__((address_space(5)))
+
+void func_pchar(__private__ char *x);
+
+void test_cast(char *gen_ptr) {
+ // CHECK: %[[cast:.*]] = addrspacecast i8* %{{.*}} to i8 addrspace(5)*
+ // CHECK-NEXT: store i8 addrspace(5)* %[[cast]]
+ __private__ char *priv_ptr = (__private__ char *)gen_ptr;
+
+ // CHECK: %[[cast:.*]] = addrspacecast i8* %{{.*}} to i8 addrspace(5)*
+ // CHECK-NEXT: call void @_Z10func_pcharPU3AS5c(i8 addrspace(5)* %[[cast]])
+ func_pchar((__private__ char *)gen_ptr);
+}
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