1 //===--- TargetInfo.h - Expose information about the target -----*- C++ -*-===//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
10 /// Defines the clang::TargetInfo interface.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_CLANG_BASIC_TARGETINFO_H
15 #define LLVM_CLANG_BASIC_TARGETINFO_H
17 #include "clang/Basic/AddressSpaces.h"
18 #include "clang/Basic/LLVM.h"
19 #include "clang/Basic/Specifiers.h"
20 #include "clang/Basic/TargetCXXABI.h"
21 #include "clang/Basic/TargetOptions.h"
22 #include "llvm/ADT/APInt.h"
23 #include "llvm/ADT/IntrusiveRefCntPtr.h"
24 #include "llvm/ADT/Optional.h"
25 #include "llvm/ADT/SmallSet.h"
26 #include "llvm/ADT/StringMap.h"
27 #include "llvm/ADT/StringRef.h"
28 #include "llvm/ADT/Triple.h"
29 #include "llvm/IR/DataLayout.h"
30 #include "llvm/Support/DataTypes.h"
31 #include "llvm/Support/VersionTuple.h"
41 class DiagnosticsEngine;
49 namespace Builtin { struct Info; }
51 /// Fields controlling how types are laid out in memory; these may need to
52 /// be copied for targets like AMDGPU that base their ABIs on an auxiliary
54 struct TransferrableTargetInfo {
55 unsigned char PointerWidth, PointerAlign;
56 unsigned char BoolWidth, BoolAlign;
57 unsigned char IntWidth, IntAlign;
58 unsigned char HalfWidth, HalfAlign;
59 unsigned char FloatWidth, FloatAlign;
60 unsigned char DoubleWidth, DoubleAlign;
61 unsigned char LongDoubleWidth, LongDoubleAlign, Float128Align;
62 unsigned char LargeArrayMinWidth, LargeArrayAlign;
63 unsigned char LongWidth, LongAlign;
64 unsigned char LongLongWidth, LongLongAlign;
66 // Fixed point bit widths
67 unsigned char ShortAccumWidth, ShortAccumAlign;
68 unsigned char AccumWidth, AccumAlign;
69 unsigned char LongAccumWidth, LongAccumAlign;
70 unsigned char ShortFractWidth, ShortFractAlign;
71 unsigned char FractWidth, FractAlign;
72 unsigned char LongFractWidth, LongFractAlign;
74 // If true, unsigned fixed point types have the same number of fractional bits
75 // as their signed counterparts, forcing the unsigned types to have one extra
76 // bit of padding. Otherwise, unsigned fixed point types have
77 // one more fractional bit than its corresponding signed type. This is false
79 bool PaddingOnUnsignedFixedPoint;
81 // Fixed point integral and fractional bit sizes
82 // Saturated types share the same integral/fractional bits as their
83 // corresponding unsaturated types.
84 // For simplicity, the fractional bits in a _Fract type will be one less the
85 // width of that _Fract type. This leaves all signed _Fract types having no
86 // padding and unsigned _Fract types will only have 1 bit of padding after the
87 // sign if PaddingOnUnsignedFixedPoint is set.
88 unsigned char ShortAccumScale;
89 unsigned char AccumScale;
90 unsigned char LongAccumScale;
92 unsigned char SuitableAlign;
93 unsigned char DefaultAlignForAttributeAligned;
94 unsigned char MinGlobalAlign;
96 unsigned short NewAlign;
97 unsigned short MaxVectorAlign;
98 unsigned short MaxTLSAlign;
100 const llvm::fltSemantics *HalfFormat, *FloatFormat, *DoubleFormat,
101 *LongDoubleFormat, *Float128Format;
103 ///===---- Target Data Type Query Methods -------------------------------===//
126 IntType SizeType, IntMaxType, PtrDiffType, IntPtrType, WCharType,
127 WIntType, Char16Type, Char32Type, Int64Type, SigAtomicType,
130 /// Whether Objective-C's built-in boolean type should be signed char.
132 /// Otherwise, when this flag is not set, the normal built-in boolean type is
134 unsigned UseSignedCharForObjCBool : 1;
136 /// Control whether the alignment of bit-field types is respected when laying
137 /// out structures. If true, then the alignment of the bit-field type will be
138 /// used to (a) impact the alignment of the containing structure, and (b)
139 /// ensure that the individual bit-field will not straddle an alignment
141 unsigned UseBitFieldTypeAlignment : 1;
143 /// Whether zero length bitfields (e.g., int : 0;) force alignment of
144 /// the next bitfield.
146 /// If the alignment of the zero length bitfield is greater than the member
147 /// that follows it, `bar', `bar' will be aligned as the type of the
148 /// zero-length bitfield.
149 unsigned UseZeroLengthBitfieldAlignment : 1;
151 /// Whether explicit bit field alignment attributes are honored.
152 unsigned UseExplicitBitFieldAlignment : 1;
154 /// If non-zero, specifies a fixed alignment value for bitfields that follow
155 /// zero length bitfield, regardless of the zero length bitfield type.
156 unsigned ZeroLengthBitfieldBoundary;
159 /// Exposes information about the current target.
161 class TargetInfo : public virtual TransferrableTargetInfo,
162 public RefCountedBase<TargetInfo> {
163 std::shared_ptr<TargetOptions> TargetOpts;
166 // Target values set by the ctor of the actual target implementation. Default
167 // values are specified by the TargetInfo constructor.
171 bool NoAsmVariants; // True if {|} are normal characters.
172 bool HasLegalHalfType; // True if the backend supports operations on the half
177 unsigned char MaxAtomicPromoteWidth, MaxAtomicInlineWidth;
178 unsigned short SimdDefaultAlign;
179 std::unique_ptr<llvm::DataLayout> DataLayout;
180 const char *MCountName;
181 unsigned char RegParmMax, SSERegParmMax;
182 TargetCXXABI TheCXXABI;
183 const LangASMap *AddrSpaceMap;
185 mutable StringRef PlatformName;
186 mutable VersionTuple PlatformMinVersion;
188 unsigned HasAlignMac68kSupport : 1;
189 unsigned RealTypeUsesObjCFPRet : 3;
190 unsigned ComplexLongDoubleUsesFP2Ret : 1;
192 unsigned HasBuiltinMSVaList : 1;
194 unsigned IsRenderScriptTarget : 1;
196 // TargetInfo Constructor. Default initializes all fields.
197 TargetInfo(const llvm::Triple &T);
199 void resetDataLayout(StringRef DL) {
200 DataLayout.reset(new llvm::DataLayout(DL));
204 /// Construct a target for the given options.
206 /// \param Opts - The options to use to initialize the target. The target may
207 /// modify the options to canonicalize the target feature information to match
208 /// what the backend expects.
210 CreateTargetInfo(DiagnosticsEngine &Diags,
211 const std::shared_ptr<TargetOptions> &Opts);
213 virtual ~TargetInfo();
215 /// Retrieve the target options.
216 TargetOptions &getTargetOpts() const {
217 assert(TargetOpts && "Missing target options");
221 /// The different kinds of __builtin_va_list types defined by
222 /// the target implementation.
223 enum BuiltinVaListKind {
224 /// typedef char* __builtin_va_list;
225 CharPtrBuiltinVaList = 0,
227 /// typedef void* __builtin_va_list;
228 VoidPtrBuiltinVaList,
230 /// __builtin_va_list as defined by the AArch64 ABI
231 /// http://infocenter.arm.com/help/topic/com.arm.doc.ihi0055a/IHI0055A_aapcs64.pdf
232 AArch64ABIBuiltinVaList,
234 /// __builtin_va_list as defined by the PNaCl ABI:
235 /// http://www.chromium.org/nativeclient/pnacl/bitcode-abi#TOC-Machine-Types
236 PNaClABIBuiltinVaList,
238 /// __builtin_va_list as defined by the Power ABI:
239 /// https://www.power.org
240 /// /resources/downloads/Power-Arch-32-bit-ABI-supp-1.0-Embedded.pdf
241 PowerABIBuiltinVaList,
243 /// __builtin_va_list as defined by the x86-64 ABI:
244 /// http://refspecs.linuxbase.org/elf/x86_64-abi-0.21.pdf
245 X86_64ABIBuiltinVaList,
247 /// __builtin_va_list as defined by ARM AAPCS ABI
248 /// http://infocenter.arm.com
249 // /help/topic/com.arm.doc.ihi0042d/IHI0042D_aapcs.pdf
250 AAPCSABIBuiltinVaList,
252 // typedef struct __va_list_tag
256 // void *__overflow_arg_area;
257 // void *__reg_save_area;
263 /// Specify if mangling based on address space map should be used or
264 /// not for language specific address spaces
265 bool UseAddrSpaceMapMangling;
268 IntType getSizeType() const { return SizeType; }
269 IntType getSignedSizeType() const {
277 case UnsignedLongLong:
278 return SignedLongLong;
280 llvm_unreachable("Invalid SizeType");
283 IntType getIntMaxType() const { return IntMaxType; }
284 IntType getUIntMaxType() const {
285 return getCorrespondingUnsignedType(IntMaxType);
287 IntType getPtrDiffType(unsigned AddrSpace) const {
288 return AddrSpace == 0 ? PtrDiffType : getPtrDiffTypeV(AddrSpace);
290 IntType getUnsignedPtrDiffType(unsigned AddrSpace) const {
291 return getCorrespondingUnsignedType(getPtrDiffType(AddrSpace));
293 IntType getIntPtrType() const { return IntPtrType; }
294 IntType getUIntPtrType() const {
295 return getCorrespondingUnsignedType(IntPtrType);
297 IntType getWCharType() const { return WCharType; }
298 IntType getWIntType() const { return WIntType; }
299 IntType getChar16Type() const { return Char16Type; }
300 IntType getChar32Type() const { return Char32Type; }
301 IntType getInt64Type() const { return Int64Type; }
302 IntType getUInt64Type() const {
303 return getCorrespondingUnsignedType(Int64Type);
305 IntType getSigAtomicType() const { return SigAtomicType; }
306 IntType getProcessIDType() const { return ProcessIDType; }
308 static IntType getCorrespondingUnsignedType(IntType T) {
313 return UnsignedShort;
319 return UnsignedLongLong;
321 llvm_unreachable("Unexpected signed integer type");
325 /// In the event this target uses the same number of fractional bits for its
326 /// unsigned types as it does with its signed counterparts, there will be
327 /// exactly one bit of padding.
328 /// Return true if unsigned fixed point types have padding for this target.
329 bool doUnsignedFixedPointTypesHavePadding() const {
330 return PaddingOnUnsignedFixedPoint;
333 /// Return the width (in bits) of the specified integer type enum.
335 /// For example, SignedInt -> getIntWidth().
336 unsigned getTypeWidth(IntType T) const;
338 /// Return integer type with specified width.
339 virtual IntType getIntTypeByWidth(unsigned BitWidth, bool IsSigned) const;
341 /// Return the smallest integer type with at least the specified width.
342 virtual IntType getLeastIntTypeByWidth(unsigned BitWidth,
343 bool IsSigned) const;
345 /// Return floating point type with specified width.
346 RealType getRealTypeByWidth(unsigned BitWidth) const;
348 /// Return the alignment (in bits) of the specified integer type enum.
350 /// For example, SignedInt -> getIntAlign().
351 unsigned getTypeAlign(IntType T) const;
353 /// Returns true if the type is signed; false otherwise.
354 static bool isTypeSigned(IntType T);
356 /// Return the width of pointers on this target, for the
357 /// specified address space.
358 uint64_t getPointerWidth(unsigned AddrSpace) const {
359 return AddrSpace == 0 ? PointerWidth : getPointerWidthV(AddrSpace);
361 uint64_t getPointerAlign(unsigned AddrSpace) const {
362 return AddrSpace == 0 ? PointerAlign : getPointerAlignV(AddrSpace);
365 /// Return the maximum width of pointers on this target.
366 virtual uint64_t getMaxPointerWidth() const {
370 /// Get integer value for null pointer.
371 /// \param AddrSpace address space of pointee in source language.
372 virtual uint64_t getNullPointerValue(LangAS AddrSpace) const { return 0; }
374 /// Return the size of '_Bool' and C++ 'bool' for this target, in bits.
375 unsigned getBoolWidth() const { return BoolWidth; }
377 /// Return the alignment of '_Bool' and C++ 'bool' for this target.
378 unsigned getBoolAlign() const { return BoolAlign; }
380 unsigned getCharWidth() const { return 8; } // FIXME
381 unsigned getCharAlign() const { return 8; } // FIXME
383 /// Return the size of 'signed short' and 'unsigned short' for this
385 unsigned getShortWidth() const { return 16; } // FIXME
387 /// Return the alignment of 'signed short' and 'unsigned short' for
389 unsigned getShortAlign() const { return 16; } // FIXME
391 /// getIntWidth/Align - Return the size of 'signed int' and 'unsigned int' for
392 /// this target, in bits.
393 unsigned getIntWidth() const { return IntWidth; }
394 unsigned getIntAlign() const { return IntAlign; }
396 /// getLongWidth/Align - Return the size of 'signed long' and 'unsigned long'
397 /// for this target, in bits.
398 unsigned getLongWidth() const { return LongWidth; }
399 unsigned getLongAlign() const { return LongAlign; }
401 /// getLongLongWidth/Align - Return the size of 'signed long long' and
402 /// 'unsigned long long' for this target, in bits.
403 unsigned getLongLongWidth() const { return LongLongWidth; }
404 unsigned getLongLongAlign() const { return LongLongAlign; }
406 /// getShortAccumWidth/Align - Return the size of 'signed short _Accum' and
407 /// 'unsigned short _Accum' for this target, in bits.
408 unsigned getShortAccumWidth() const { return ShortAccumWidth; }
409 unsigned getShortAccumAlign() const { return ShortAccumAlign; }
411 /// getAccumWidth/Align - Return the size of 'signed _Accum' and
412 /// 'unsigned _Accum' for this target, in bits.
413 unsigned getAccumWidth() const { return AccumWidth; }
414 unsigned getAccumAlign() const { return AccumAlign; }
416 /// getLongAccumWidth/Align - Return the size of 'signed long _Accum' and
417 /// 'unsigned long _Accum' for this target, in bits.
418 unsigned getLongAccumWidth() const { return LongAccumWidth; }
419 unsigned getLongAccumAlign() const { return LongAccumAlign; }
421 /// getShortFractWidth/Align - Return the size of 'signed short _Fract' and
422 /// 'unsigned short _Fract' for this target, in bits.
423 unsigned getShortFractWidth() const { return ShortFractWidth; }
424 unsigned getShortFractAlign() const { return ShortFractAlign; }
426 /// getFractWidth/Align - Return the size of 'signed _Fract' and
427 /// 'unsigned _Fract' for this target, in bits.
428 unsigned getFractWidth() const { return FractWidth; }
429 unsigned getFractAlign() const { return FractAlign; }
431 /// getLongFractWidth/Align - Return the size of 'signed long _Fract' and
432 /// 'unsigned long _Fract' for this target, in bits.
433 unsigned getLongFractWidth() const { return LongFractWidth; }
434 unsigned getLongFractAlign() const { return LongFractAlign; }
436 /// getShortAccumScale/IBits - Return the number of fractional/integral bits
437 /// in a 'signed short _Accum' type.
438 unsigned getShortAccumScale() const { return ShortAccumScale; }
439 unsigned getShortAccumIBits() const {
440 return ShortAccumWidth - ShortAccumScale - 1;
443 /// getAccumScale/IBits - Return the number of fractional/integral bits
444 /// in a 'signed _Accum' type.
445 unsigned getAccumScale() const { return AccumScale; }
446 unsigned getAccumIBits() const { return AccumWidth - AccumScale - 1; }
448 /// getLongAccumScale/IBits - Return the number of fractional/integral bits
449 /// in a 'signed long _Accum' type.
450 unsigned getLongAccumScale() const { return LongAccumScale; }
451 unsigned getLongAccumIBits() const {
452 return LongAccumWidth - LongAccumScale - 1;
455 /// getUnsignedShortAccumScale/IBits - Return the number of
456 /// fractional/integral bits in a 'unsigned short _Accum' type.
457 unsigned getUnsignedShortAccumScale() const {
458 return PaddingOnUnsignedFixedPoint ? ShortAccumScale : ShortAccumScale + 1;
460 unsigned getUnsignedShortAccumIBits() const {
461 return PaddingOnUnsignedFixedPoint
462 ? getShortAccumIBits()
463 : ShortAccumWidth - getUnsignedShortAccumScale();
466 /// getUnsignedAccumScale/IBits - Return the number of fractional/integral
467 /// bits in a 'unsigned _Accum' type.
468 unsigned getUnsignedAccumScale() const {
469 return PaddingOnUnsignedFixedPoint ? AccumScale : AccumScale + 1;
471 unsigned getUnsignedAccumIBits() const {
472 return PaddingOnUnsignedFixedPoint ? getAccumIBits()
473 : AccumWidth - getUnsignedAccumScale();
476 /// getUnsignedLongAccumScale/IBits - Return the number of fractional/integral
477 /// bits in a 'unsigned long _Accum' type.
478 unsigned getUnsignedLongAccumScale() const {
479 return PaddingOnUnsignedFixedPoint ? LongAccumScale : LongAccumScale + 1;
481 unsigned getUnsignedLongAccumIBits() const {
482 return PaddingOnUnsignedFixedPoint
483 ? getLongAccumIBits()
484 : LongAccumWidth - getUnsignedLongAccumScale();
487 /// getShortFractScale - Return the number of fractional bits
488 /// in a 'signed short _Fract' type.
489 unsigned getShortFractScale() const { return ShortFractWidth - 1; }
491 /// getFractScale - Return the number of fractional bits
492 /// in a 'signed _Fract' type.
493 unsigned getFractScale() const { return FractWidth - 1; }
495 /// getLongFractScale - Return the number of fractional bits
496 /// in a 'signed long _Fract' type.
497 unsigned getLongFractScale() const { return LongFractWidth - 1; }
499 /// getUnsignedShortFractScale - Return the number of fractional bits
500 /// in a 'unsigned short _Fract' type.
501 unsigned getUnsignedShortFractScale() const {
502 return PaddingOnUnsignedFixedPoint ? getShortFractScale()
503 : getShortFractScale() + 1;
506 /// getUnsignedFractScale - Return the number of fractional bits
507 /// in a 'unsigned _Fract' type.
508 unsigned getUnsignedFractScale() const {
509 return PaddingOnUnsignedFixedPoint ? getFractScale() : getFractScale() + 1;
512 /// getUnsignedLongFractScale - Return the number of fractional bits
513 /// in a 'unsigned long _Fract' type.
514 unsigned getUnsignedLongFractScale() const {
515 return PaddingOnUnsignedFixedPoint ? getLongFractScale()
516 : getLongFractScale() + 1;
519 /// Determine whether the __int128 type is supported on this target.
520 virtual bool hasInt128Type() const {
521 return (getPointerWidth(0) >= 64) || getTargetOpts().ForceEnableInt128;
524 /// Determine whether _Float16 is supported on this target.
525 virtual bool hasLegalHalfType() const { return HasLegalHalfType; }
527 /// Determine whether the __float128 type is supported on this target.
528 virtual bool hasFloat128Type() const { return HasFloat128; }
530 /// Determine whether the _Float16 type is supported on this target.
531 virtual bool hasFloat16Type() const { return HasFloat16; }
533 /// Return the alignment that is suitable for storing any
534 /// object with a fundamental alignment requirement.
535 unsigned getSuitableAlign() const { return SuitableAlign; }
537 /// Return the default alignment for __attribute__((aligned)) on
538 /// this target, to be used if no alignment value is specified.
539 unsigned getDefaultAlignForAttributeAligned() const {
540 return DefaultAlignForAttributeAligned;
543 /// getMinGlobalAlign - Return the minimum alignment of a global variable,
544 /// unless its alignment is explicitly reduced via attributes.
545 virtual unsigned getMinGlobalAlign (uint64_t) const {
546 return MinGlobalAlign;
549 /// Return the largest alignment for which a suitably-sized allocation with
550 /// '::operator new(size_t)' is guaranteed to produce a correctly-aligned
552 unsigned getNewAlign() const {
553 return NewAlign ? NewAlign : std::max(LongDoubleAlign, LongLongAlign);
556 /// getWCharWidth/Align - Return the size of 'wchar_t' for this target, in
558 unsigned getWCharWidth() const { return getTypeWidth(WCharType); }
559 unsigned getWCharAlign() const { return getTypeAlign(WCharType); }
561 /// getChar16Width/Align - Return the size of 'char16_t' for this target, in
563 unsigned getChar16Width() const { return getTypeWidth(Char16Type); }
564 unsigned getChar16Align() const { return getTypeAlign(Char16Type); }
566 /// getChar32Width/Align - Return the size of 'char32_t' for this target, in
568 unsigned getChar32Width() const { return getTypeWidth(Char32Type); }
569 unsigned getChar32Align() const { return getTypeAlign(Char32Type); }
571 /// getHalfWidth/Align/Format - Return the size/align/format of 'half'.
572 unsigned getHalfWidth() const { return HalfWidth; }
573 unsigned getHalfAlign() const { return HalfAlign; }
574 const llvm::fltSemantics &getHalfFormat() const { return *HalfFormat; }
576 /// getFloatWidth/Align/Format - Return the size/align/format of 'float'.
577 unsigned getFloatWidth() const { return FloatWidth; }
578 unsigned getFloatAlign() const { return FloatAlign; }
579 const llvm::fltSemantics &getFloatFormat() const { return *FloatFormat; }
581 /// getDoubleWidth/Align/Format - Return the size/align/format of 'double'.
582 unsigned getDoubleWidth() const { return DoubleWidth; }
583 unsigned getDoubleAlign() const { return DoubleAlign; }
584 const llvm::fltSemantics &getDoubleFormat() const { return *DoubleFormat; }
586 /// getLongDoubleWidth/Align/Format - Return the size/align/format of 'long
588 unsigned getLongDoubleWidth() const { return LongDoubleWidth; }
589 unsigned getLongDoubleAlign() const { return LongDoubleAlign; }
590 const llvm::fltSemantics &getLongDoubleFormat() const {
591 return *LongDoubleFormat;
594 /// getFloat128Width/Align/Format - Return the size/align/format of
596 unsigned getFloat128Width() const { return 128; }
597 unsigned getFloat128Align() const { return Float128Align; }
598 const llvm::fltSemantics &getFloat128Format() const {
599 return *Float128Format;
602 /// Return the mangled code of long double.
603 virtual const char *getLongDoubleMangling() const { return "e"; }
605 /// Return the mangled code of __float128.
606 virtual const char *getFloat128Mangling() const { return "g"; }
608 /// Return the value for the C99 FLT_EVAL_METHOD macro.
609 virtual unsigned getFloatEvalMethod() const { return 0; }
611 // getLargeArrayMinWidth/Align - Return the minimum array size that is
612 // 'large' and its alignment.
613 unsigned getLargeArrayMinWidth() const { return LargeArrayMinWidth; }
614 unsigned getLargeArrayAlign() const { return LargeArrayAlign; }
616 /// Return the maximum width lock-free atomic operation which will
617 /// ever be supported for the given target
618 unsigned getMaxAtomicPromoteWidth() const { return MaxAtomicPromoteWidth; }
619 /// Return the maximum width lock-free atomic operation which can be
620 /// inlined given the supported features of the given target.
621 unsigned getMaxAtomicInlineWidth() const { return MaxAtomicInlineWidth; }
622 /// Set the maximum inline or promote width lock-free atomic operation
623 /// for the given target.
624 virtual void setMaxAtomicWidth() {}
625 /// Returns true if the given target supports lock-free atomic
626 /// operations at the specified width and alignment.
627 virtual bool hasBuiltinAtomic(uint64_t AtomicSizeInBits,
628 uint64_t AlignmentInBits) const {
629 return AtomicSizeInBits <= AlignmentInBits &&
630 AtomicSizeInBits <= getMaxAtomicInlineWidth() &&
631 (AtomicSizeInBits <= getCharWidth() ||
632 llvm::isPowerOf2_64(AtomicSizeInBits / getCharWidth()));
635 /// Return the maximum vector alignment supported for the given target.
636 unsigned getMaxVectorAlign() const { return MaxVectorAlign; }
637 /// Return default simd alignment for the given target. Generally, this
638 /// value is type-specific, but this alignment can be used for most of the
639 /// types for the given target.
640 unsigned getSimdDefaultAlign() const { return SimdDefaultAlign; }
642 /// Return the alignment (in bits) of the thrown exception object. This is
643 /// only meaningful for targets that allocate C++ exceptions in a system
644 /// runtime, such as those using the Itanium C++ ABI.
645 virtual unsigned getExnObjectAlignment() const {
646 // Itanium says that an _Unwind_Exception has to be "double-word"
647 // aligned (and thus the end of it is also so-aligned), meaning 16
648 // bytes. Of course, that was written for the actual Itanium,
649 // which is a 64-bit platform. Classically, the ABI doesn't really
650 // specify the alignment on other platforms, but in practice
651 // libUnwind declares the struct with __attribute__((aligned)), so
652 // we assume that alignment here. (It's generally 16 bytes, but
653 // some targets overwrite it.)
654 return getDefaultAlignForAttributeAligned();
657 /// Return the size of intmax_t and uintmax_t for this target, in bits.
658 unsigned getIntMaxTWidth() const {
659 return getTypeWidth(IntMaxType);
662 // Return the size of unwind_word for this target.
663 virtual unsigned getUnwindWordWidth() const { return getPointerWidth(0); }
665 /// Return the "preferred" register width on this target.
666 virtual unsigned getRegisterWidth() const {
667 // Currently we assume the register width on the target matches the pointer
668 // width, we can introduce a new variable for this if/when some target wants
673 /// Returns the name of the mcount instrumentation function.
674 const char *getMCountName() const {
678 /// Check if the Objective-C built-in boolean type should be signed
681 /// Otherwise, if this returns false, the normal built-in boolean type
682 /// should also be used for Objective-C.
683 bool useSignedCharForObjCBool() const {
684 return UseSignedCharForObjCBool;
686 void noSignedCharForObjCBool() {
687 UseSignedCharForObjCBool = false;
690 /// Check whether the alignment of bit-field types is respected
691 /// when laying out structures.
692 bool useBitFieldTypeAlignment() const {
693 return UseBitFieldTypeAlignment;
696 /// Check whether zero length bitfields should force alignment of
698 bool useZeroLengthBitfieldAlignment() const {
699 return UseZeroLengthBitfieldAlignment;
702 /// Get the fixed alignment value in bits for a member that follows
703 /// a zero length bitfield.
704 unsigned getZeroLengthBitfieldBoundary() const {
705 return ZeroLengthBitfieldBoundary;
708 /// Check whether explicit bitfield alignment attributes should be
709 // honored, as in "__attribute__((aligned(2))) int b : 1;".
710 bool useExplicitBitFieldAlignment() const {
711 return UseExplicitBitFieldAlignment;
714 /// Check whether this target support '\#pragma options align=mac68k'.
715 bool hasAlignMac68kSupport() const {
716 return HasAlignMac68kSupport;
719 /// Return the user string for the specified integer type enum.
721 /// For example, SignedShort -> "short".
722 static const char *getTypeName(IntType T);
724 /// Return the constant suffix for the specified integer type enum.
726 /// For example, SignedLong -> "L".
727 const char *getTypeConstantSuffix(IntType T) const;
729 /// Return the printf format modifier for the specified
730 /// integer type enum.
732 /// For example, SignedLong -> "l".
733 static const char *getTypeFormatModifier(IntType T);
735 /// Check whether the given real type should use the "fpret" flavor of
736 /// Objective-C message passing on this target.
737 bool useObjCFPRetForRealType(RealType T) const {
738 return RealTypeUsesObjCFPRet & (1 << T);
741 /// Check whether _Complex long double should use the "fp2ret" flavor
742 /// of Objective-C message passing on this target.
743 bool useObjCFP2RetForComplexLongDouble() const {
744 return ComplexLongDoubleUsesFP2Ret;
747 /// Check whether llvm intrinsics such as llvm.convert.to.fp16 should be used
748 /// to convert to and from __fp16.
749 /// FIXME: This function should be removed once all targets stop using the
750 /// conversion intrinsics.
751 virtual bool useFP16ConversionIntrinsics() const {
755 /// Specify if mangling based on address space map should be used or
756 /// not for language specific address spaces
757 bool useAddressSpaceMapMangling() const {
758 return UseAddrSpaceMapMangling;
761 ///===---- Other target property query methods --------------------------===//
763 /// Appends the target-specific \#define values for this
764 /// target set to the specified buffer.
765 virtual void getTargetDefines(const LangOptions &Opts,
766 MacroBuilder &Builder) const = 0;
769 /// Return information about target-specific builtins for
770 /// the current primary target, and info about which builtins are non-portable
771 /// across the current set of primary and secondary targets.
772 virtual ArrayRef<Builtin::Info> getTargetBuiltins() const = 0;
774 /// The __builtin_clz* and __builtin_ctz* built-in
775 /// functions are specified to have undefined results for zero inputs, but
776 /// on targets that support these operations in a way that provides
777 /// well-defined results for zero without loss of performance, it is a good
778 /// idea to avoid optimizing based on that undef behavior.
779 virtual bool isCLZForZeroUndef() const { return true; }
781 /// Returns the kind of __builtin_va_list type that should be used
782 /// with this target.
783 virtual BuiltinVaListKind getBuiltinVaListKind() const = 0;
785 /// Returns whether or not type \c __builtin_ms_va_list type is
786 /// available on this target.
787 bool hasBuiltinMSVaList() const { return HasBuiltinMSVaList; }
789 /// Returns true for RenderScript.
790 bool isRenderScriptTarget() const { return IsRenderScriptTarget; }
792 /// Returns whether the passed in string is a valid clobber in an
793 /// inline asm statement.
795 /// This is used by Sema.
796 bool isValidClobber(StringRef Name) const;
798 /// Returns whether the passed in string is a valid register name
799 /// according to GCC.
801 /// This is used by Sema for inline asm statements.
802 virtual bool isValidGCCRegisterName(StringRef Name) const;
804 /// Returns the "normalized" GCC register name.
806 /// ReturnCannonical true will return the register name without any additions
807 /// such as "{}" or "%" in it's canonical form, for example:
808 /// ReturnCanonical = true and Name = "rax", will return "ax".
809 StringRef getNormalizedGCCRegisterName(StringRef Name,
810 bool ReturnCanonical = false) const;
812 /// Extracts a register from the passed constraint (if it is a
813 /// single-register constraint) and the asm label expression related to a
814 /// variable in the input or output list of an inline asm statement.
816 /// This function is used by Sema in order to diagnose conflicts between
817 /// the clobber list and the input/output lists.
818 virtual StringRef getConstraintRegister(StringRef Constraint,
819 StringRef Expression) const {
823 struct ConstraintInfo {
826 CI_AllowsMemory = 0x01,
827 CI_AllowsRegister = 0x02,
828 CI_ReadWrite = 0x04, // "+r" output constraint (read and write).
829 CI_HasMatchingInput = 0x08, // This output operand has a matching input.
830 CI_ImmediateConstant = 0x10, // This operand must be an immediate constant
831 CI_EarlyClobber = 0x20, // "&" output constraint (early clobber).
840 llvm::SmallSet<int, 4> ImmSet;
842 std::string ConstraintStr; // constraint: "=rm"
843 std::string Name; // Operand name: [foo] with no []'s.
845 ConstraintInfo(StringRef ConstraintStr, StringRef Name)
846 : Flags(0), TiedOperand(-1), ConstraintStr(ConstraintStr.str()),
848 ImmRange.Min = ImmRange.Max = 0;
849 ImmRange.isConstrained = false;
852 const std::string &getConstraintStr() const { return ConstraintStr; }
853 const std::string &getName() const { return Name; }
854 bool isReadWrite() const { return (Flags & CI_ReadWrite) != 0; }
855 bool earlyClobber() { return (Flags & CI_EarlyClobber) != 0; }
856 bool allowsRegister() const { return (Flags & CI_AllowsRegister) != 0; }
857 bool allowsMemory() const { return (Flags & CI_AllowsMemory) != 0; }
859 /// Return true if this output operand has a matching
860 /// (tied) input operand.
861 bool hasMatchingInput() const { return (Flags & CI_HasMatchingInput) != 0; }
863 /// Return true if this input operand is a matching
864 /// constraint that ties it to an output operand.
866 /// If this returns true then getTiedOperand will indicate which output
867 /// operand this is tied to.
868 bool hasTiedOperand() const { return TiedOperand != -1; }
869 unsigned getTiedOperand() const {
870 assert(hasTiedOperand() && "Has no tied operand!");
871 return (unsigned)TiedOperand;
874 bool requiresImmediateConstant() const {
875 return (Flags & CI_ImmediateConstant) != 0;
877 bool isValidAsmImmediate(const llvm::APInt &Value) const {
879 return Value.isSignedIntN(32) &&
880 ImmSet.count(Value.getZExtValue()) != 0;
881 return !ImmRange.isConstrained ||
882 (Value.sge(ImmRange.Min) && Value.sle(ImmRange.Max));
885 void setIsReadWrite() { Flags |= CI_ReadWrite; }
886 void setEarlyClobber() { Flags |= CI_EarlyClobber; }
887 void setAllowsMemory() { Flags |= CI_AllowsMemory; }
888 void setAllowsRegister() { Flags |= CI_AllowsRegister; }
889 void setHasMatchingInput() { Flags |= CI_HasMatchingInput; }
890 void setRequiresImmediate(int Min, int Max) {
891 Flags |= CI_ImmediateConstant;
894 ImmRange.isConstrained = true;
896 void setRequiresImmediate(llvm::ArrayRef<int> Exacts) {
897 Flags |= CI_ImmediateConstant;
898 for (int Exact : Exacts)
899 ImmSet.insert(Exact);
901 void setRequiresImmediate(int Exact) {
902 Flags |= CI_ImmediateConstant;
903 ImmSet.insert(Exact);
905 void setRequiresImmediate() {
906 Flags |= CI_ImmediateConstant;
909 /// Indicate that this is an input operand that is tied to
910 /// the specified output operand.
912 /// Copy over the various constraint information from the output.
913 void setTiedOperand(unsigned N, ConstraintInfo &Output) {
914 Output.setHasMatchingInput();
915 Flags = Output.Flags;
917 // Don't copy Name or constraint string.
921 /// Validate register name used for global register variables.
923 /// This function returns true if the register passed in RegName can be used
924 /// for global register variables on this target. In addition, it returns
925 /// true in HasSizeMismatch if the size of the register doesn't match the
926 /// variable size passed in RegSize.
927 virtual bool validateGlobalRegisterVariable(StringRef RegName,
929 bool &HasSizeMismatch) const {
930 HasSizeMismatch = false;
934 // validateOutputConstraint, validateInputConstraint - Checks that
935 // a constraint is valid and provides information about it.
936 // FIXME: These should return a real error instead of just true/false.
937 bool validateOutputConstraint(ConstraintInfo &Info) const;
938 bool validateInputConstraint(MutableArrayRef<ConstraintInfo> OutputConstraints,
939 ConstraintInfo &info) const;
941 virtual bool validateOutputSize(StringRef /*Constraint*/,
942 unsigned /*Size*/) const {
946 virtual bool validateInputSize(StringRef /*Constraint*/,
947 unsigned /*Size*/) const {
951 validateConstraintModifier(StringRef /*Constraint*/,
954 std::string &/*SuggestedModifier*/) const {
958 validateAsmConstraint(const char *&Name,
959 TargetInfo::ConstraintInfo &info) const = 0;
961 bool resolveSymbolicName(const char *&Name,
962 ArrayRef<ConstraintInfo> OutputConstraints,
963 unsigned &Index) const;
965 // Constraint parm will be left pointing at the last character of
966 // the constraint. In practice, it won't be changed unless the
967 // constraint is longer than one character.
968 virtual std::string convertConstraint(const char *&Constraint) const {
969 // 'p' defaults to 'r', but can be overridden by targets.
970 if (*Constraint == 'p')
971 return std::string("r");
972 return std::string(1, *Constraint);
975 /// Returns a string of target-specific clobbers, in LLVM format.
976 virtual const char *getClobbers() const = 0;
978 /// Returns true if NaN encoding is IEEE 754-2008.
979 /// Only MIPS allows a different encoding.
980 virtual bool isNan2008() const {
984 /// Returns the target triple of the primary target.
985 const llvm::Triple &getTriple() const {
989 const llvm::DataLayout &getDataLayout() const {
990 assert(DataLayout && "Uninitialized DataLayout!");
995 const char * const Aliases[5];
996 const char * const Register;
1000 const char * const Names[5];
1001 const unsigned RegNum;
1004 /// Does this target support "protected" visibility?
1006 /// Any target which dynamic libraries will naturally support
1007 /// something like "default" (meaning that the symbol is visible
1008 /// outside this shared object) and "hidden" (meaning that it isn't)
1009 /// visibilities, but "protected" is really an ELF-specific concept
1010 /// with weird semantics designed around the convenience of dynamic
1011 /// linker implementations. Which is not to suggest that there's
1012 /// consistent target-independent semantics for "default" visibility
1013 /// either; the entire thing is pretty badly mangled.
1014 virtual bool hasProtectedVisibility() const { return true; }
1016 /// An optional hook that targets can implement to perform semantic
1017 /// checking on attribute((section("foo"))) specifiers.
1019 /// In this case, "foo" is passed in to be checked. If the section
1020 /// specifier is invalid, the backend should return a non-empty string
1021 /// that indicates the problem.
1023 /// This hook is a simple quality of implementation feature to catch errors
1024 /// and give good diagnostics in cases when the assembler or code generator
1025 /// would otherwise reject the section specifier.
1027 virtual std::string isValidSectionSpecifier(StringRef SR) const {
1031 /// Set forced language options.
1033 /// Apply changes to the target information with respect to certain
1034 /// language options which change the target configuration and adjust
1035 /// the language based on the target options where applicable.
1036 virtual void adjust(LangOptions &Opts);
1038 /// Adjust target options based on codegen options.
1039 virtual void adjustTargetOptions(const CodeGenOptions &CGOpts,
1040 TargetOptions &TargetOpts) const {}
1042 /// Initialize the map with the default set of target features for the
1043 /// CPU this should include all legal feature strings on the target.
1045 /// \return False on error (invalid features).
1046 virtual bool initFeatureMap(llvm::StringMap<bool> &Features,
1047 DiagnosticsEngine &Diags, StringRef CPU,
1048 const std::vector<std::string> &FeatureVec) const;
1050 /// Get the ABI currently in use.
1051 virtual StringRef getABI() const { return StringRef(); }
1053 /// Get the C++ ABI currently in use.
1054 TargetCXXABI getCXXABI() const {
1058 /// Target the specified CPU.
1060 /// \return False on error (invalid CPU name).
1061 virtual bool setCPU(const std::string &Name) {
1065 /// Fill a SmallVectorImpl with the valid values to setCPU.
1066 virtual void fillValidCPUList(SmallVectorImpl<StringRef> &Values) const {}
1068 /// brief Determine whether this TargetInfo supports the given CPU name.
1069 virtual bool isValidCPUName(StringRef Name) const {
1073 /// Use the specified ABI.
1075 /// \return False on error (invalid ABI name).
1076 virtual bool setABI(const std::string &Name) {
1080 /// Use the specified unit for FP math.
1082 /// \return False on error (invalid unit name).
1083 virtual bool setFPMath(StringRef Name) {
1087 /// Enable or disable a specific target feature;
1088 /// the feature name must be valid.
1089 virtual void setFeatureEnabled(llvm::StringMap<bool> &Features,
1091 bool Enabled) const {
1092 Features[Name] = Enabled;
1095 /// Determine whether this TargetInfo supports the given feature.
1096 virtual bool isValidFeatureName(StringRef Feature) const {
1100 /// Perform initialization based on the user configured
1101 /// set of features (e.g., +sse4).
1103 /// The list is guaranteed to have at most one entry per feature.
1105 /// The target may modify the features list, to change which options are
1106 /// passed onwards to the backend.
1107 /// FIXME: This part should be fixed so that we can change handleTargetFeatures
1108 /// to merely a TargetInfo initialization routine.
1110 /// \return False on error.
1111 virtual bool handleTargetFeatures(std::vector<std::string> &Features,
1112 DiagnosticsEngine &Diags) {
1116 /// Determine whether the given target has the given feature.
1117 virtual bool hasFeature(StringRef Feature) const {
1121 /// Identify whether this target supports multiversioning of functions,
1122 /// which requires support for cpu_supports and cpu_is functionality.
1123 bool supportsMultiVersioning() const {
1124 return getTriple().getArch() == llvm::Triple::x86 ||
1125 getTriple().getArch() == llvm::Triple::x86_64;
1128 /// Identify whether this target supports IFuncs.
1129 bool supportsIFunc() const { return getTriple().isOSBinFormatELF(); }
1131 // Validate the contents of the __builtin_cpu_supports(const char*)
1133 virtual bool validateCpuSupports(StringRef Name) const { return false; }
1135 // Return the target-specific priority for features/cpus/vendors so
1136 // that they can be properly sorted for checking.
1137 virtual unsigned multiVersionSortPriority(StringRef Name) const {
1141 // Validate the contents of the __builtin_cpu_is(const char*)
1143 virtual bool validateCpuIs(StringRef Name) const { return false; }
1145 // Validate a cpu_dispatch/cpu_specific CPU option, which is a different list
1146 // from cpu_is, since it checks via features rather than CPUs directly.
1147 virtual bool validateCPUSpecificCPUDispatch(StringRef Name) const {
1151 // Get the character to be added for mangling purposes for cpu_specific.
1152 virtual char CPUSpecificManglingCharacter(StringRef Name) const {
1154 "cpu_specific Multiversioning not implemented on this target");
1157 // Get a list of the features that make up the CPU option for
1158 // cpu_specific/cpu_dispatch so that it can be passed to llvm as optimization
1160 virtual void getCPUSpecificCPUDispatchFeatures(
1161 StringRef Name, llvm::SmallVectorImpl<StringRef> &Features) const {
1163 "cpu_specific Multiversioning not implemented on this target");
1166 // Returns maximal number of args passed in registers.
1167 unsigned getRegParmMax() const {
1168 assert(RegParmMax < 7 && "RegParmMax value is larger than AST can handle");
1172 /// Whether the target supports thread-local storage.
1173 bool isTLSSupported() const {
1174 return TLSSupported;
1177 /// Return the maximum alignment (in bits) of a TLS variable
1179 /// Gets the maximum alignment (in bits) of a TLS variable on this target.
1180 /// Returns zero if there is no such constraint.
1181 unsigned short getMaxTLSAlign() const {
1185 /// Whether target supports variable-length arrays.
1186 bool isVLASupported() const { return VLASupported; }
1188 /// Whether the target supports SEH __try.
1189 bool isSEHTrySupported() const {
1190 return getTriple().isOSWindows() &&
1191 (getTriple().getArch() == llvm::Triple::x86 ||
1192 getTriple().getArch() == llvm::Triple::x86_64 ||
1193 getTriple().getArch() == llvm::Triple::aarch64);
1196 /// Return true if {|} are normal characters in the asm string.
1198 /// If this returns false (the default), then {abc|xyz} is syntax
1199 /// that says that when compiling for asm variant #0, "abc" should be
1200 /// generated, but when compiling for asm variant #1, "xyz" should be
1202 bool hasNoAsmVariants() const {
1203 return NoAsmVariants;
1206 /// Return the register number that __builtin_eh_return_regno would
1207 /// return with the specified argument.
1208 /// This corresponds with TargetLowering's getExceptionPointerRegister
1209 /// and getExceptionSelectorRegister in the backend.
1210 virtual int getEHDataRegisterNumber(unsigned RegNo) const {
1214 /// Return the section to use for C++ static initialization functions.
1215 virtual const char *getStaticInitSectionSpecifier() const {
1219 const LangASMap &getAddressSpaceMap() const { return *AddrSpaceMap; }
1221 /// Map from the address space field in builtin description strings to the
1222 /// language address space.
1223 virtual LangAS getOpenCLBuiltinAddressSpace(unsigned AS) const {
1224 return getLangASFromTargetAS(AS);
1227 /// Map from the address space field in builtin description strings to the
1228 /// language address space.
1229 virtual LangAS getCUDABuiltinAddressSpace(unsigned AS) const {
1230 return getLangASFromTargetAS(AS);
1233 /// Return an AST address space which can be used opportunistically
1234 /// for constant global memory. It must be possible to convert pointers into
1235 /// this address space to LangAS::Default. If no such address space exists,
1236 /// this may return None, and such optimizations will be disabled.
1237 virtual llvm::Optional<LangAS> getConstantAddressSpace() const {
1238 return LangAS::Default;
1241 /// Retrieve the name of the platform as it is used in the
1242 /// availability attribute.
1243 StringRef getPlatformName() const { return PlatformName; }
1245 /// Retrieve the minimum desired version of the platform, to
1246 /// which the program should be compiled.
1247 VersionTuple getPlatformMinVersion() const { return PlatformMinVersion; }
1249 bool isBigEndian() const { return BigEndian; }
1250 bool isLittleEndian() const { return !BigEndian; }
1252 enum CallingConvMethodType {
1258 /// Gets the default calling convention for the given target and
1259 /// declaration context.
1260 virtual CallingConv getDefaultCallingConv(CallingConvMethodType MT) const {
1261 // Not all targets will specify an explicit calling convention that we can
1262 // express. This will always do the right thing, even though it's not
1263 // an explicit calling convention.
1267 enum CallingConvCheckResult {
1273 /// Determines whether a given calling convention is valid for the
1274 /// target. A calling convention can either be accepted, produce a warning
1275 /// and be substituted with the default calling convention, or (someday)
1276 /// produce an error (such as using thiscall on a non-instance function).
1277 virtual CallingConvCheckResult checkCallingConvention(CallingConv CC) const {
1280 return CCCR_Warning;
1286 enum CallingConvKind {
1292 virtual CallingConvKind getCallingConvKind(bool ClangABICompat4) const;
1294 /// Controls if __builtin_longjmp / __builtin_setjmp can be lowered to
1295 /// llvm.eh.sjlj.longjmp / llvm.eh.sjlj.setjmp.
1296 virtual bool hasSjLjLowering() const {
1300 /// Check if the target supports CFProtection branch.
1302 checkCFProtectionBranchSupported(DiagnosticsEngine &Diags) const;
1304 /// Check if the target supports CFProtection branch.
1306 checkCFProtectionReturnSupported(DiagnosticsEngine &Diags) const;
1308 /// Whether target allows to overalign ABI-specified preferred alignment
1309 virtual bool allowsLargerPreferedTypeAlignment() const { return true; }
1311 /// Set supported OpenCL extensions and optional core features.
1312 virtual void setSupportedOpenCLOpts() {}
1314 /// Set supported OpenCL extensions as written on command line
1315 virtual void setOpenCLExtensionOpts() {
1316 for (const auto &Ext : getTargetOpts().OpenCLExtensionsAsWritten) {
1317 getTargetOpts().SupportedOpenCLOptions.support(Ext);
1321 /// Get supported OpenCL extensions and optional core features.
1322 OpenCLOptions &getSupportedOpenCLOpts() {
1323 return getTargetOpts().SupportedOpenCLOptions;
1326 /// Get const supported OpenCL extensions and optional core features.
1327 const OpenCLOptions &getSupportedOpenCLOpts() const {
1328 return getTargetOpts().SupportedOpenCLOptions;
1331 enum OpenCLTypeKind {
1342 /// Get address space for OpenCL type.
1343 virtual LangAS getOpenCLTypeAddrSpace(OpenCLTypeKind TK) const;
1345 /// \returns Target specific vtbl ptr address space.
1346 virtual unsigned getVtblPtrAddressSpace() const {
1350 /// \returns If a target requires an address within a target specific address
1351 /// space \p AddressSpace to be converted in order to be used, then return the
1352 /// corresponding target specific DWARF address space.
1354 /// \returns Otherwise return None and no conversion will be emitted in the
1356 virtual Optional<unsigned> getDWARFAddressSpace(unsigned AddressSpace) const {
1360 /// \returns The version of the SDK which was used during the compilation if
1361 /// one was specified, or an empty version otherwise.
1362 const llvm::VersionTuple &getSDKVersion() const {
1363 return getTargetOpts().SDKVersion;
1366 /// Check the target is valid after it is fully initialized.
1367 virtual bool validateTarget(DiagnosticsEngine &Diags) const {
1371 virtual void setAuxTarget(const TargetInfo *Aux) {}
1374 /// Copy type and layout related info.
1375 void copyAuxTarget(const TargetInfo *Aux);
1376 virtual uint64_t getPointerWidthV(unsigned AddrSpace) const {
1377 return PointerWidth;
1379 virtual uint64_t getPointerAlignV(unsigned AddrSpace) const {
1380 return PointerAlign;
1382 virtual enum IntType getPtrDiffTypeV(unsigned AddrSpace) const {
1385 virtual ArrayRef<const char *> getGCCRegNames() const = 0;
1386 virtual ArrayRef<GCCRegAlias> getGCCRegAliases() const = 0;
1387 virtual ArrayRef<AddlRegName> getGCCAddlRegNames() const {
1392 // Assert the values for the fractional and integral bits for each fixed point
1393 // type follow the restrictions given in clause 6.2.6.3 of N1169.
1394 void CheckFixedPointBits() const;
1397 } // end namespace clang