1 //===---- TargetInfo.h - Encapsulate target details -------------*- C++ -*-===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // These classes wrap the information about a call or function
11 // definition used to handle ABI compliancy.
12 //
13 //===----------------------------------------------------------------------===//
14 
15 #ifndef LLVM_CLANG_LIB_CODEGEN_TARGETINFO_H
16 #define LLVM_CLANG_LIB_CODEGEN_TARGETINFO_H
17 
18 #include "CodeGenModule.h"
19 #include "CGValue.h"
20 #include "clang/AST/Type.h"
21 #include "clang/Basic/LLVM.h"
22 #include "llvm/ADT/SmallString.h"
23 #include "llvm/ADT/StringRef.h"
24 
25 namespace llvm {
26 class Constant;
27 class GlobalValue;
28 class Type;
29 class Value;
30 }
31 
32 namespace clang {
33 class Decl;
34 
35 namespace CodeGen {
36 class ABIInfo;
37 class CallArgList;
38 class CodeGenFunction;
39 class CGFunctionInfo;
40 
41 /// TargetCodeGenInfo - This class organizes various target-specific
42 /// codegeneration issues, like target-specific attributes, builtins and so
43 /// on.
44 class TargetCodeGenInfo {
45   ABIInfo *Info;
46 
47 public:
48   // WARNING: Acquires the ownership of ABIInfo.
49   TargetCodeGenInfo(ABIInfo *info = nullptr) : Info(info) {}
50   virtual ~TargetCodeGenInfo();
51 
52   /// getABIInfo() - Returns ABI info helper for the target.
53   const ABIInfo &getABIInfo() const { return *Info; }
54 
55   /// setTargetAttributes - Provides a convenient hook to handle extra
56   /// target-specific attributes for the given global.
57   virtual void setTargetAttributes(const Decl *D, llvm::GlobalValue *GV,
58                                    CodeGen::CodeGenModule &M,
59                                    ForDefinition_t IsForDefinition) const {}
60 
61   /// emitTargetMD - Provides a convenient hook to handle extra
62   /// target-specific metadata for the given global.
63   virtual void emitTargetMD(const Decl *D, llvm::GlobalValue *GV,
64                             CodeGen::CodeGenModule &M) const {}
65 
66   /// Determines the size of struct _Unwind_Exception on this platform,
67   /// in 8-bit units.  The Itanium ABI defines this as:
68   ///   struct _Unwind_Exception {
69   ///     uint64 exception_class;
70   ///     _Unwind_Exception_Cleanup_Fn exception_cleanup;
71   ///     uint64 private_1;
72   ///     uint64 private_2;
73   ///   };
74   virtual unsigned getSizeOfUnwindException() const;
75 
76   /// Controls whether __builtin_extend_pointer should sign-extend
77   /// pointers to uint64_t or zero-extend them (the default).  Has
78   /// no effect for targets:
79   ///   - that have 64-bit pointers, or
80   ///   - that cannot address through registers larger than pointers, or
81   ///   - that implicitly ignore/truncate the top bits when addressing
82   ///     through such registers.
83   virtual bool extendPointerWithSExt() const { return false; }
84 
85   /// Determines the DWARF register number for the stack pointer, for
86   /// exception-handling purposes.  Implements __builtin_dwarf_sp_column.
87   ///
88   /// Returns -1 if the operation is unsupported by this target.
89   virtual int getDwarfEHStackPointer(CodeGen::CodeGenModule &M) const {
90     return -1;
91   }
92 
93   /// Initializes the given DWARF EH register-size table, a char*.
94   /// Implements __builtin_init_dwarf_reg_size_table.
95   ///
96   /// Returns true if the operation is unsupported by this target.
97   virtual bool initDwarfEHRegSizeTable(CodeGen::CodeGenFunction &CGF,
98                                        llvm::Value *Address) const {
99     return true;
100   }
101 
102   /// Performs the code-generation required to convert a return
103   /// address as stored by the system into the actual address of the
104   /// next instruction that will be executed.
105   ///
106   /// Used by __builtin_extract_return_addr().
107   virtual llvm::Value *decodeReturnAddress(CodeGen::CodeGenFunction &CGF,
108                                            llvm::Value *Address) const {
109     return Address;
110   }
111 
112   /// Performs the code-generation required to convert the address
113   /// of an instruction into a return address suitable for storage
114   /// by the system in a return slot.
115   ///
116   /// Used by __builtin_frob_return_addr().
117   virtual llvm::Value *encodeReturnAddress(CodeGen::CodeGenFunction &CGF,
118                                            llvm::Value *Address) const {
119     return Address;
120   }
121 
122   /// Corrects the low-level LLVM type for a given constraint and "usual"
123   /// type.
124   ///
125   /// \returns A pointer to a new LLVM type, possibly the same as the original
126   /// on success; 0 on failure.
127   virtual llvm::Type *adjustInlineAsmType(CodeGen::CodeGenFunction &CGF,
128                                           StringRef Constraint,
129                                           llvm::Type *Ty) const {
130     return Ty;
131   }
132 
133   /// Adds constraints and types for result registers.
134   virtual void addReturnRegisterOutputs(
135       CodeGen::CodeGenFunction &CGF, CodeGen::LValue ReturnValue,
136       std::string &Constraints, std::vector<llvm::Type *> &ResultRegTypes,
137       std::vector<llvm::Type *> &ResultTruncRegTypes,
138       std::vector<CodeGen::LValue> &ResultRegDests, std::string &AsmString,
139       unsigned NumOutputs) const {}
140 
141   /// doesReturnSlotInterfereWithArgs - Return true if the target uses an
142   /// argument slot for an 'sret' type.
143   virtual bool doesReturnSlotInterfereWithArgs() const { return true; }
144 
145   /// Retrieve the address of a function to call immediately before
146   /// calling objc_retainAutoreleasedReturnValue.  The
147   /// implementation of objc_autoreleaseReturnValue sniffs the
148   /// instruction stream following its return address to decide
149   /// whether it's a call to objc_retainAutoreleasedReturnValue.
150   /// This can be prohibitively expensive, depending on the
151   /// relocation model, and so on some targets it instead sniffs for
152   /// a particular instruction sequence.  This functions returns
153   /// that instruction sequence in inline assembly, which will be
154   /// empty if none is required.
155   virtual StringRef getARCRetainAutoreleasedReturnValueMarker() const {
156     return "";
157   }
158 
159   /// Return a constant used by UBSan as a signature to identify functions
160   /// possessing type information, or 0 if the platform is unsupported.
161   virtual llvm::Constant *
162   getUBSanFunctionSignature(CodeGen::CodeGenModule &CGM) const {
163     return nullptr;
164   }
165 
166   /// Determine whether a call to an unprototyped functions under
167   /// the given calling convention should use the variadic
168   /// convention or the non-variadic convention.
169   ///
170   /// There's a good reason to make a platform's variadic calling
171   /// convention be different from its non-variadic calling
172   /// convention: the non-variadic arguments can be passed in
173   /// registers (better for performance), and the variadic arguments
174   /// can be passed on the stack (also better for performance).  If
175   /// this is done, however, unprototyped functions *must* use the
176   /// non-variadic convention, because C99 states that a call
177   /// through an unprototyped function type must succeed if the
178   /// function was defined with a non-variadic prototype with
179   /// compatible parameters.  Therefore, splitting the conventions
180   /// makes it impossible to call a variadic function through an
181   /// unprototyped type.  Since function prototypes came out in the
182   /// late 1970s, this is probably an acceptable trade-off.
183   /// Nonetheless, not all platforms are willing to make it, and in
184   /// particularly x86-64 bends over backwards to make the
185   /// conventions compatible.
186   ///
187   /// The default is false.  This is correct whenever:
188   ///   - the conventions are exactly the same, because it does not
189   ///     matter and the resulting IR will be somewhat prettier in
190   ///     certain cases; or
191   ///   - the conventions are substantively different in how they pass
192   ///     arguments, because in this case using the variadic convention
193   ///     will lead to C99 violations.
194   ///
195   /// However, some platforms make the conventions identical except
196   /// for passing additional out-of-band information to a variadic
197   /// function: for example, x86-64 passes the number of SSE
198   /// arguments in %al.  On these platforms, it is desirable to
199   /// call unprototyped functions using the variadic convention so
200   /// that unprototyped calls to varargs functions still succeed.
201   ///
202   /// Relatedly, platforms which pass the fixed arguments to this:
203   ///   A foo(B, C, D);
204   /// differently than they would pass them to this:
205   ///   A foo(B, C, D, ...);
206   /// may need to adjust the debugger-support code in Sema to do the
207   /// right thing when calling a function with no know signature.
208   virtual bool isNoProtoCallVariadic(const CodeGen::CallArgList &args,
209                                      const FunctionNoProtoType *fnType) const;
210 
211   /// Gets the linker options necessary to link a dependent library on this
212   /// platform.
213   virtual void getDependentLibraryOption(llvm::StringRef Lib,
214                                          llvm::SmallString<24> &Opt) const;
215 
216   /// Gets the linker options necessary to detect object file mismatches on
217   /// this platform.
218   virtual void getDetectMismatchOption(llvm::StringRef Name,
219                                        llvm::StringRef Value,
220                                        llvm::SmallString<32> &Opt) const {}
221 
222   /// Get LLVM calling convention for OpenCL kernel.
223   virtual unsigned getOpenCLKernelCallingConv() const;
224 
225   /// Get target specific null pointer.
226   /// \param T is the LLVM type of the null pointer.
227   /// \param QT is the clang QualType of the null pointer.
228   /// \return ConstantPointerNull with the given type \p T.
229   /// Each target can override it to return its own desired constant value.
230   virtual llvm::Constant *getNullPointer(const CodeGen::CodeGenModule &CGM,
231       llvm::PointerType *T, QualType QT) const;
232 
233   /// Get target favored AST address space of a global variable for languages
234   /// other than OpenCL and CUDA.
235   /// If \p D is nullptr, returns the default target favored address space
236   /// for global variable.
237   virtual unsigned getGlobalVarAddressSpace(CodeGenModule &CGM,
238                                             const VarDecl *D) const;
239 
240   /// Get the AST address space for alloca.
241   virtual unsigned getASTAllocaAddressSpace() const { return LangAS::Default; }
242 
243   /// Perform address space cast of an expression of pointer type.
244   /// \param V is the LLVM value to be casted to another address space.
245   /// \param SrcAddr is the language address space of \p V.
246   /// \param DestAddr is the targeted language address space.
247   /// \param DestTy is the destination LLVM pointer type.
248   /// \param IsNonNull is the flag indicating \p V is known to be non null.
249   virtual llvm::Value *performAddrSpaceCast(CodeGen::CodeGenFunction &CGF,
250                                             llvm::Value *V, unsigned SrcAddr,
251                                             unsigned DestAddr,
252                                             llvm::Type *DestTy,
253                                             bool IsNonNull = false) const;
254 
255   /// Perform address space cast of a constant expression of pointer type.
256   /// \param V is the LLVM constant to be casted to another address space.
257   /// \param SrcAddr is the language address space of \p V.
258   /// \param DestAddr is the targeted language address space.
259   /// \param DestTy is the destination LLVM pointer type.
260   virtual llvm::Constant *
261   performAddrSpaceCast(CodeGenModule &CGM, llvm::Constant *V, unsigned SrcAddr,
262                        unsigned DestAddr, llvm::Type *DestTy) const;
263 };
264 
265 } // namespace CodeGen
266 } // namespace clang
267 
268 #endif // LLVM_CLANG_LIB_CODEGEN_TARGETINFO_H
269