Add support for non-zero null pointer for C and OpenCL
In amdgcn target, null pointers in global, constant, and generic address space take value 0 but null pointers in private and local address space take value -1. Currently LLVM assumes all null pointers take value 0, which results in incorrectly translated IR. To workaround this issue, instead of emit null pointers in local and private address space, a null pointer in generic address space is emitted and casted to local and private address space.
Tentative definition of global variables with non-zero initializer will have weak linkage instead of common linkage since common linkage requires zero initializer and does not have explicit section to hold the non-zero value.
Virtual member functions getNullPointer and performAddrSpaceCast are added to TargetCodeGenInfo which by default returns ConstantPointerNull and emitting addrspacecast instruction. A virtual member function getNullPointerValue is added to TargetInfo which by default returns 0. Each target can override these virtual functions to get target specific null pointer and the null pointer value for specific address space, and perform specific translations for addrspacecast.
Wrapper functions getNullPointer is added to CodegenModule and getTargetNullPointerValue is added to ASTContext to facilitate getting the target specific null pointers and their values.
This change has no effect on other targets except amdgcn target. Other targets can provide support of non-zero null pointer in a similar way.
This change only provides support for non-zero null pointer for C and OpenCL. Supporting for other languages will be added later incrementally.
Differential Revision: https://reviews.llvm.org/D26196
llvm-svn: 289252
diff --git a/clang/lib/CodeGen/CGExprConstant.cpp b/clang/lib/CodeGen/CGExprConstant.cpp
index 27c8386..f657309 100644
--- a/clang/lib/CodeGen/CGExprConstant.cpp
+++ b/clang/lib/CodeGen/CGExprConstant.cpp
@@ -16,6 +16,7 @@
#include "CGObjCRuntime.h"
#include "CGRecordLayout.h"
#include "CodeGenModule.h"
+#include "TargetInfo.h"
#include "clang/AST/APValue.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/RecordLayout.h"
@@ -1262,6 +1263,10 @@
return C;
}
+llvm::Constant *CodeGenModule::getNullPointer(llvm::PointerType *T, QualType QT) {
+ return getTargetCodeGenInfo().getNullPointer(*this, T, QT);
+}
+
llvm::Constant *CodeGenModule::EmitConstantValue(const APValue &Value,
QualType DestType,
CodeGenFunction *CGF) {
@@ -1293,6 +1298,7 @@
llvm::ConstantInt::get(Int64Ty, Value.getLValueOffset().getQuantity());
llvm::Constant *C = nullptr;
+
if (APValue::LValueBase LVBase = Value.getLValueBase()) {
// An array can be represented as an lvalue referring to the base.
if (isa<llvm::ArrayType>(DestTy)) {
@@ -1323,7 +1329,9 @@
// Convert to the appropriate type; this could be an lvalue for
// an integer.
- if (isa<llvm::PointerType>(DestTy)) {
+ if (auto PT = dyn_cast<llvm::PointerType>(DestTy)) {
+ if (Value.isNullPointer())
+ return getNullPointer(PT, DestType);
// Convert the integer to a pointer-sized integer before converting it
// to a pointer.
C = llvm::ConstantExpr::getIntegerCast(
@@ -1510,7 +1518,7 @@
const CXXRecordDecl *base);
static llvm::Constant *EmitNullConstant(CodeGenModule &CGM,
- const CXXRecordDecl *record,
+ const RecordDecl *record,
bool asCompleteObject) {
const CGRecordLayout &layout = CGM.getTypes().getCGRecordLayout(record);
llvm::StructType *structure =
@@ -1520,25 +1528,29 @@
unsigned numElements = structure->getNumElements();
std::vector<llvm::Constant *> elements(numElements);
+ auto CXXR = dyn_cast<CXXRecordDecl>(record);
// Fill in all the bases.
- for (const auto &I : record->bases()) {
- if (I.isVirtual()) {
- // Ignore virtual bases; if we're laying out for a complete
- // object, we'll lay these out later.
- continue;
+ if (CXXR) {
+ for (const auto &I : CXXR->bases()) {
+ if (I.isVirtual()) {
+ // Ignore virtual bases; if we're laying out for a complete
+ // object, we'll lay these out later.
+ continue;
+ }
+
+ const CXXRecordDecl *base =
+ cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
+
+ // Ignore empty bases.
+ if (base->isEmpty() ||
+ CGM.getContext().getASTRecordLayout(base).getNonVirtualSize()
+ .isZero())
+ continue;
+
+ unsigned fieldIndex = layout.getNonVirtualBaseLLVMFieldNo(base);
+ llvm::Type *baseType = structure->getElementType(fieldIndex);
+ elements[fieldIndex] = EmitNullConstantForBase(CGM, baseType, base);
}
-
- const CXXRecordDecl *base =
- cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
-
- // Ignore empty bases.
- if (base->isEmpty() ||
- CGM.getContext().getASTRecordLayout(base).getNonVirtualSize().isZero())
- continue;
-
- unsigned fieldIndex = layout.getNonVirtualBaseLLVMFieldNo(base);
- llvm::Type *baseType = structure->getElementType(fieldIndex);
- elements[fieldIndex] = EmitNullConstantForBase(CGM, baseType, base);
}
// Fill in all the fields.
@@ -1562,8 +1574,8 @@
}
// Fill in the virtual bases, if we're working with the complete object.
- if (asCompleteObject) {
- for (const auto &I : record->vbases()) {
+ if (CXXR && asCompleteObject) {
+ for (const auto &I : CXXR->vbases()) {
const CXXRecordDecl *base =
cast<CXXRecordDecl>(I.getType()->castAs<RecordType>()->getDecl());
@@ -1605,6 +1617,10 @@
}
llvm::Constant *CodeGenModule::EmitNullConstant(QualType T) {
+ if (auto PT = T->getAs<PointerType>())
+ return getNullPointer(cast<llvm::PointerType>(getTypes().ConvertTypeForMem(T)),
+ T);
+
if (getTypes().isZeroInitializable(T))
return llvm::Constant::getNullValue(getTypes().ConvertTypeForMem(T));
@@ -1620,10 +1636,8 @@
return llvm::ConstantArray::get(ATy, Array);
}
- if (const RecordType *RT = T->getAs<RecordType>()) {
- const CXXRecordDecl *RD = cast<CXXRecordDecl>(RT->getDecl());
- return ::EmitNullConstant(*this, RD, /*complete object*/ true);
- }
+ if (const RecordType *RT = T->getAs<RecordType>())
+ return ::EmitNullConstant(*this, RT->getDecl(), /*complete object*/ true);
assert(T->isMemberDataPointerType() &&
"Should only see pointers to data members here!");