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Arm инструкции ассемблера

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Корпорация Raza Microelectronics выкупили производственную линию у менее успешных SandCraft, а затем начала выпускать восьмиядерные устройства для рынка телекоммуникаций и сетей. Cavium Networks, изначально являвшиеся поставщиком средств защиты процессоров, тоже начали производство восьми-, а позже и ядерных архитектур для тех же рынков. Обе компании сами проектировали ядра, и лишь лицензировали разработки вместо того, чтобы покупать готовые проекты процессоров MIPS.

В числе операционных систем, портированных на архитектуру MIPS: В е годы MIPS-архитектура была широко распространена на рынке встраиваемых систем: Низкое энергопотребление и температурные характеристики встраиваемых MIPS-архитектур, широкие возможности внутренних функций делают этот микропроцессор универсальным для многих устройств. В последние годы большинство технологий, используемых в различных поколениях MIPS, предложены в виде IP-ядер стандартных блоков для встраиваемых реализаций процессора.

Некогда коммерчески успешные ядра MIPS и в настоящее время нашли потребительское и промышленное применение. Процессоры под управлением MIPS включают в себя: Одним из наиболее интересных применений архитектуры MIPS является их использование в многопроцессорных вычислительных суперкомпьютерах.

В начале х компания Silicon Graphics SGI перенаправила свой бизнес с графических терминалов на рынок высокопроизводительного вычисления. Успех первых попыток компании в области серверных систем а именно, серия Challenge, основанная на R, R и R мотивировал SGI создать гораздо более мощную систему. В году корпорация SiCortex представила новый многопроцессорный персональный суперкомпьютер, основанный на архитектуре MIPS. В его разработку легли MIPS64 и высокопроизводительная межсистемная связь с использованием топологии графов Кауца англ.

Данная система является предельно эффективной и вычислительно мощной. И все это на одном кристалле, который потребляет 10 Вт энергии, но выполняет максимум 6 миллиардов операций с плавающей запятой в секунду. Так как производство процессоров Loongson было более дешёвым, MIPS получили возможность возродиться на рынке персональных компьютеров в лице Loongson.

Эта модель была разработана для того, чтобы повысить производительность графических 3D-приложений. Но вскоре их объединили, и в конечном итоге в году эти проекты были отменены. Чтобы работать с этим типом данных в режиме SIMD , были добавлены различные варианты арифметических, сравнительных операций над числами с плавающей запятой, а также команда условного перехода.

Появились новые инструкции для загрузки, реконфигурации и преобразования PS-данных. Это первая архитектура, сумевшая реализовать обработку чисел с плавающей запятой в SIMD -режиме с имеющимися ресурсами. Первым коммерческим микропроцессором с архитектурой MIPS был микропроцессор R, представленный в году. В нём были реализованы операции умножения и деления, которые выполнялись за несколько тактов. Устройство умножения и деления не было тесно интегрировано в ядро процессора, хотя и размещалось на том же кристалле; по этой причине система команд расширена инструкциями для загрузки результатов умножения и деления в регистры общего назначения, эти инструкции блокировали конвейер.

Микропроцессор R мог быть загружен как в режиме big-endian, так и в режиме little-endian, содержал тридцать два разрядных регистра общего назначения. Следует отметить, что счётчик команд непосредственно недоступен.

Микропроцессор R поддерживал подключение до четырёх сопроцессоров, один из которых является встроенным и обеспечивает работу с исключениями, а также управление памятью MMU. В случае необходимости в качестве ещё одного сопроцессора можно было подключить микросхему R, арифметический сопроцессор, который содержал тридцать два разрядных регистра, которые можно было использовать как шестнадцать разрядных регистров для работы с числами двойной точности.

Следующим в семействе стал R , который появился в году. Кроме того, R обеспечивал когерентность кэш-памяти при работе в мультипроцессорных конфигурациях. Несмотря на то, что в поддержке мультипроцессорности R имеется ряд недостатков, на базе R было создано несколько работоспособных многопроцессорных систем.

Микропроцессор R стал первым коммерчески успешным процессором с архитектурой MIPS, было изготовлено более миллиона процессоров. Другие производители также представили процессоры, совместимые с RA: Первой системой на кристалле, использующей процессор с архитектурой MIPS, стала разработка R фирмы Toshiba; данная микросхема использовалась в портативном компьютере, работавшем под управлением Windows CE.

Был разработан радиационно-устойчивый вариант R с интегрированным R, предназначенный для применения в космических аппаратах, который получил название Mongoose-V. В этом процессоре внешняя тактовая частота 50 МГц удваивается, а внутренняя тактовая частота составляет МГц.

Набор команд этих процессоров спецификация MIPS II был расширен командами загрузки и записи разрядных чисел с плавающей запятой, командами вычисления квадратного корня с одинарной и двойной точностью, командами условных прерываний, а также атомарными операциями, необходимыми для поддержки мультипроцессорных конфигураций.

В процессорах R и R реализованы битовые шины данных и битовые регистры. Если в R увеличили тактовую частоту, но пожертвовали количеством кэш-памяти, то QED уделили большое внимание и ёмкости кэш-памяти доступ к которой можно получить всего за 2 цикла , и эффективному использованию поверхности кристалла.

В процессоре R FPU диспетчеризация операций с плавающей запятой одинарной точности была более гибкой, чем в R, и, вследствие этого, рабочие станции SGI Indys, базированные на R отличались лучшей графической производительностью, чем R с такой же тактовой скоростью и графическим аппаратным устройством.

Чтобы подчеркнуть улучшение после объединения R и старой графической платы, SGI дала ей новое название. Процессор RM включал в себя Кб встроенной кэш-памяти 2го уровня и контроллер для дополнительной кэш-памяти 3го уровня. R представлен в году был первой суперскалярной архитектурой MIPS, способной осуществлять 2 целочисленные инструкции или с плавающей запятой и 2 инструкции обращения к памяти за один цикл.

Данная разработка использовала 6 схем: Архитектура имеет два полностью конвейеризованных устройства умножения-сложения с двойной точностью , которые могут передавать поток данных в 4 Мб внекристального вторичного кэша. Хотя производительность этого FPU и была наиболее подходящей для научных сотрудников, ограниченность его целочисленной производительности и высокая цена не смогли привлечь большинство пользователей, поэтому R был на рынке всего год, и даже сейчас его едва ли можно найти.

DICompileUnit nodes represent a compile unit. Compile unit descriptors provide the root scope for objects declared in a specific compilation unit. File descriptors are defined using this scope.

These descriptors are collected by a named metadata node! They keep track of global variables, type information, and imported entities declarations and namespaces. DIFile nodes represent files. Files are sometimes used in scope: Valid values for checksumkind: DIBasicType nodes represent primitive types, such as int , bool and float. DISubroutineType nodes represent subroutine types. DIDerivedType nodes represent types derived from other types, such as qualified types. The type of the member is the baseType: If the composite type has an ODR identifier: DIFwdDecl , then the member is uniqued based only on its name: DICompositeType nodes represent types composed of other types, like structures and unions.

If the source language supports ODR, the identifier: When specified, subprogram declarations and member derived types that reference the ODR-type in their scope: For a given identifier: LLVM tools that link modules together will unique such definitions at parse time via the identifier: The DIFlagVector flag to flags: All enumeration type descriptors are collected in the enums: DITemplateTypeParameter nodes represent type parameters to generic source language constructs.

DITemplateValueParameter nodes represent value parameters to generic source language constructs. DINamespace nodes represent namespaces in the source language. DIGlobalVariable nodes represent global variables in the source language. All global variables should be referenced by the globals: DISubprogram nodes represent functions from the source language.

A DISubprogram may be attached to a function definition using! If the scope is a composite type with an ODR identifier: DIFwdDecl , then the subprogram declaration is uniqued based only on its linkageName: DILexicalBlock nodes describe nested blocks within a subprogram. The line number and column numbers are used to distinguish two lexical blocks at same depth.

They are valid targets for scope: Usually lexical blocks are distinct to prevent node merging based on operands. DILexicalBlockFile nodes are used to discriminate between sections of a lexical block.

DILocation nodes represent source debug locations. DILocalVariable nodes represent local variables in the source language. They are used in debug intrinsics such as llvm. DWARF specifies three kinds of simple location descriptions: Register, memory, and implicit location descriptions. Register and memory location descriptions describe the location of a source variable in the sense that a debugger might modify its value , whereas implicit locations describe merely the value of a source variable.

DIExpressions also follow this model: DIImportedEntity nodes represent entities such as modules imported into a compile unit. DIMacro nodes represent definition or undefinition of a macro identifiers. DIMacroFile nodes represent inclusion of source files. Instead, metadata is added to the IR to describe a type system of a higher level language. Semantics talks about high level issues, and Representation talks about the metadata encoding of various entities. The rules mentioned in this section only pertain to TBAA nodes living under the same root.

Type Descriptors , further subdivided into scalar type descriptors and struct type descriptors; and Access Tags. Type descriptors describe the type system of the higher level language being compiled. Scalar type descriptors describe types that do not contain other types. Each scalar type has a parent type, which must also be a scalar type or the TBAA root. Via this parent relation, scalar types within a TBAA root form a tree.

Struct type descriptors denote types that contain a sequence of other type descriptors, at known offsets. These contained type descriptors can either be struct type descriptors themselves or scalar type descriptors.

Access tags are metadata nodes attached to load and store instructions. Access tags use type descriptors to describe the location being accessed in terms of the type system of the higher level language.

Access tags are tuples consisting of a base type, an access type and an offset. The base type is a scalar type descriptor or a struct type descriptor, the access type is a scalar type descriptor, and the offset is a constant integer.

Scalar type descriptors are represented as an MDNode s with two operands. The first operand is an MDString denoting the name of the struct type. The second operand is an MDNode which points to the parent for said scalar type descriptor, which is either another scalar type descriptor or the TBAA root. Scalar type descriptors can have an optional third argument, but that must be the constant integer zero. Struct type descriptors are represented as MDNode s with an odd number of operands greater than 1.

Like in scalar type descriptors the actual value of this name operand is irrelevant to LLVM. After the name operand, the struct type descriptors have a sequence of alternating MDNode and ConstantInt operands. With N starting from 1, the 2N - 1 th operand, an MDNode , denotes a contained field, and the 2N th operand, a ConstantInt , is the offset of the said contained field.

The offsets must be in non-decreasing order. Access tags are represented as MDNode s with either 3 or 4 operands. The first operand is an MDNode pointing to the node representing the base type.

The second operand is an MDNode pointing to the node representing the access type. The third operand is a ConstantInt that states the offset of the access. If a fourth field is present, it must be a ConstantInt valued at 0 or 1. The current metadata format is very simple. For each group of three, the first operand gives the byte offset of a field in bytes, the second gives its size in bytes, and the third gives its tbaa tag.

This describes a struct with two fields. The first is at offset 0 bytes with size 4 bytes, and has tbaa tag! The second is at offset 8 bytes and has size 4 bytes and has tbaa tag! Note that the fields need not be contiguous. In this example, there is a 4 byte gap between the two fields.

This gap represents padding which does not carry useful data and need not be preserved. This means that some collection of memory access instructions loads, stores, memory-accessing calls, etc. Each type of metadata specifies a list of scopes where each scope has an id and a domain. This is used for example during inlining. As the noalias function parameters are turned into noalias scope metadata, a new domain is used every time the function is inlined.

The metadata identifying each domain is itself a list containing one or two entries. The first entry is the name of the domain. Note that if the name is a string then it can be combined across functions and translation units. A self-reference can be used to create globally unique domain names. A descriptive string may optionally be provided as a second list entry.

The metadata identifying each scope is also itself a list containing two or three entries. The first entry is the name of the scope. A self-reference can be used to create globally unique scope names. A descriptive string may optionally be provided as a third list entry.

It can be used to express the maximum acceptable error in the result of that instruction, in ULPs, thus potentially allowing the compiler to use a more efficient but less accurate method of computing it. ULP is defined as follows:. The metadata node shall consist of a single positive float type number representing the maximum relative error, for example:. It expresses the possible ranges the loaded value or the value returned by the called function at this call site is in. The ranges are represented with a flattened list of integers.

The loaded value or the value returned is known to be in the union of the ranges defined by each consecutive pair.

Each pair has the following properties:. In addition, the pairs must be in signed order of the lower bound and they must be non-contiguous. If callees metadata is attached to a call site, and any callee is not among the set of functions provided by the metadata, the behavior is undefined. The intent of this metadata is to facilitate optimizations such as indirect-call promotion.

For example, in the code below, the call instruction may only target the add or sub functions:. It can be used to express the unpredictability of control flow. Similar to the llvm.

The metadata is treated as a boolean value; if it exists, it signals that the branch or switch that it is attached to is completely unpredictable. It is sometimes useful to attach information to loop constructs. Currently, loop metadata is implemented as metadata attached to the branch instruction in the loop latch block.

This type of metadata refer to a metadata node that is guaranteed to be separate for each loop. The loop identifier metadata is specified with the name llvm. The loop identifier metadata is implemented using a metadata that refers to itself to avoid merging it with any other identifier metadata, e.

That is, each loop should refer to their own identification metadata even if they reside in separate functions. The following example contains loop identifier metadata for two separate loop constructs:. The loop identifier metadata can be used to specify additional per-loop metadata.

Any operands after the first operand can be treated as user-defined metadata. For example the llvm. Metadata prefixed with llvm. These metadata should be used in conjunction with llvm.

This metadata suggests an interleave count to the loop interleaver. The first operand is the string llvm. Note that setting llvm. This metadata selectively enables or disables vectorization for the loop. If the bit operand value is 1 vectorization is enabled. A value of 0 disables vectorization:. This metadata sets the target width of the vectorizer. This metadata suggests an unroll factor to the loop unroller.

This metadata disables loop unrolling. The metadata has a single operand which is the string llvm. This metadata disables runtime loop unrolling. This metadata suggests that the loop should be fully unrolled if the trip count is known at compile time and partially unrolled if the trip count is not known at compile time. This metadata suggests that the loop should be unrolled fully.

This metadata indicates that the loop should not be versioned for the purpose of enabling loop-invariant code motion LICM.

Loop distribution allows splitting a loop into multiple loops. Currently, this is only performed if the entire loop cannot be vectorized due to unsafe memory dependencies. The transformation will attempt to isolate the unsafe dependencies into their own loop. This metadata can be used to selectively enable or disable distribution of the loop. If the bit operand value is 1 distribution is enabled. A value of 0 disables distribution:. This metadata should be used in conjunction with llvm.

Metadata types used to annotate memory accesses with information helpful for optimizations are prefixed with llvm. The metadata is attached to memory accessing instructions and denotes that no loop carried memory dependence exist between it and other instructions denoted with the same loop identifier.

The metadata on memory reads also implies that if conversion i. Precisely, given two instructions m1 and m2 that both have the llvm. As a special case, if all memory accessing instructions in a loop have llvm. Note that if not all memory access instructions have such metadata referring to the loop, then the loop is considered not being trivially parallel.

Additional memory dependence analysis is required to make that determination. As a fail safe mechanism, this causes loops that were originally parallel to be considered sequential if optimization passes that are unaware of the parallel semantics insert new memory instructions into the loop body.

Example of a loop that is considered parallel due to its correct use of both llvm. It is also possible to have nested parallel loops. In that case the memory accesses refer to a list of loop identifier metadata nodes instead of the loop identifier metadata node directly:. The intent of this metadata is to improve the accuracy of the block frequency propagation.

For example, in the code below, the block header0 may have a loop header weight relative to the other headers of the irreducible loop of The existence of the invariant. Pointers returned by bitcast or getelementptr with only zero indices are considered the same. This is because invariant. Note that this is an experimental feature, which means that its semantics might change in the future. The associated metadata may be attached to a global object declaration with a single argument that references another global object.

This metadata prevents discarding of the global object in linker GC unless the referenced object is also discarded. The linker support for this feature is spotty. For best compatibility, globals carrying this metadata may also:. The prof metadata is used to record profile data in the IR. The first operand of the metadata node indicates the profile metadata type.

There are currently 3 types: Branch weight metadata attached to a branch, select, switch or call instruction represents the likeliness of the associated branch being taken.

Function entry count metadata can be attached to function definitions to record the number of times the function is called. Used with BFI information, it is also used to derive the basic block profile count. VP value profile metadata can be attached to instructions that have value profile information. Currently this is indirect calls where it records the hottest callees and calls to memory intrinsics such as memcpy, memmove, and memset where it records the hottest byte lengths.

The value profiling kind is 0 for indirect call targets and 1 for memory operations. For indirect call targets, each profile value is a hash of the callee function name, and for memory operations each value is the byte length.

Note that the value counts do not need to add up to the total count listed in the third operand in practice only the top hottest values are tracked and reported. Note that the VP type is 0 the second operand , which indicates this is an indirect call value profile data. The third operand indicates that the indirect call executed times. Each triplet has the following form:. When two or more modules are merged together, the resulting llvm. That is, for each unique metadata ID string, there will be exactly one entry in the merged modules llvm.

The only exception is that entries with the Require behavior are always preserved. It is an error for a particular unique flag ID to have multiple behaviors, except in the case of Require which adds restrictions on another metadata value or Override. The behavior if two or more! The behavior is to emit an error if the llvm. The metadata consists of a version number and a bitmask specifying what types of garbage collection are supported if any by the file.

If two or more modules are linked together their garbage collection metadata needs to be merged rather than appended together. The Objective-C garbage collection module flags metadata consists of the following key-value pairs:. The ARM backend emits a section into each generated object file describing the options that it was compiled with in a compiler-independent way to prevent linking incompatible objects, and to allow automatic library selection.

To pass this information to the backend, these options are encoded in module flags metadata, using the following key-value pairs:. Some targets support embedding flags to the linker inside individual object files. Typically this is used in conjunction with language extensions which allow source files to explicitly declare the libraries they depend on, and have these automatically be transmitted to the linker via object files.

These flags are encoded in the IR using named metadata with the name! Each operand is expected to be a metadata node which should be a list of other metadata nodes, each of which should be a list of metadata strings defining linker options. For example, the following metadata section specifies two separate sets of linker options, presumably to link against libz and the Cocoa framework:. The metadata encoding as lists of lists of options, as opposed to a collapsed list of options, is chosen so that the IR encoding can use multiple option strings to specify e.

No other aspect of these options is defined by the IR. These are documented here. This array contains a list of pointers to named global variables, functions and aliases which may optionally have a pointer cast formed of bitcast or getelementptr. For example, a legal use of it is:. If a symbol appears in the llvm. For example, if a variable has internal linkage and no references other than that from the llvm.

On some targets, the code generator must emit a directive to the assembler or object file to prevent the assembler and linker from molesting the symbol. On targets that support it, this allows an intelligent linker to optimize references to the symbol without being impeded as it would be by llvm. This is a rare construct that should only be used in rare circumstances, and should not be exposed to source languages. The functions referenced by this array will be called in ascending order of priority i.

The order of functions with the same priority is not defined. If the third field is present, non-null, and points to a global variable or function, the initializer function will only run if the associated data from the current module is not discarded.

The functions referenced by this array will be called in descending order of priority i. If the third field is present, non-null, and points to a global variable or function, the destructor function will only run if the associated data from the current module is not discarded. The LLVM instruction set consists of several different classifications of instructions: The terminator instructions are: There are two forms of this instruction, corresponding to a conditional branch and an unconditional branch.

The table is not allowed to contain duplicate constant entries. The switch instruction specifies a table of values and destinations. If the value is found, control flow is transferred to the corresponding destination; otherwise, control flow is transferred to the default destination.

Depending on properties of the target machine and the particular switch instruction, this instruction may be code generated in different ways. For example, it could be generated as a series of chained conditional branches or with a lookup table. Address must be derived from a blockaddress constant. The rest of the arguments indicate the full set of possible destinations that the address may point to.

This destination list is required so that dataflow analysis has an accurate understanding of the CFG. Control transfers to the block specified in the address argument. All possible destination blocks must be listed in the label list, otherwise this instruction has undefined behavior. This implies that jumps to labels defined in other functions have undefined behavior as well. The primary difference is that it establishes an association with a label, which is used by the runtime library to unwind the stack.

This instruction is used in languages with destructors to ensure that proper cleanup is performed in the case of either a longjmp or a thrown exception. If the callee unwinds then no return value is available. The parent argument is the token of the funclet that contains the catchswitch instruction.

If the catchswitch is not inside a funclet, this operand may be the token none. The default argument is the label of another basic block beginning with either a cleanuppad or catchswitch instruction. This unwind destination must be a legal target with respect to the parent links, as described in the exception handling documentation. The handlers are a nonempty list of successor blocks that each begin with a catchpad instruction.

Executing this instruction transfers control to one of the successors in handlers , if appropriate, or continues to unwind via the unwind label if present. Therefore, it must be the only non-phi instruction in the block.

It must be a catchpad. The personality function gets a chance to execute arbitrary code to, for example, destroy the active exception. Control then transfers to normal. The token argument must be a token produced by a catchpad instruction. It transfers control to continue or unwinds out of the function.

This instruction is used to inform the optimizer that a particular portion of the code is not reachable. This can be used to indicate that the code after a no-return function cannot be reached, and other facts. Binary operators are used to do most of the computation in a program. They require two operands of the same type, execute an operation on them, and produce a single value. The operands might represent multiple data, as is the case with the vector data type. The result value has the same type as its operands.

Both arguments must have identical types. If the sum has unsigned overflow, the result returned is the mathematical result modulo 2 n , where n is the bit width of the result. The value produced is the floating-point sum of the two operands.

This instruction is assumed to execute in the default floating-point environment. This instruction can also take any number of fast-math flags , which are optimization hints to enable otherwise unsafe floating-point optimizations:.

If the difference has unsigned overflow, the result returned is the mathematical result modulo 2 n , where n is the bit width of the result. The value produced is the floating-point difference of the two operands. If the result of the multiplication has unsigned overflow, the result returned is the mathematical result modulo 2 n , where n is the bit width of the result. If a full product e. The value produced is the floating-point product of the two operands. Division by zero is undefined behavior.

For vectors, if any element of the divisor is zero, the operation has undefined behavior. Overflow also leads to undefined behavior; this is a rare case, but can occur, for example, by doing a bit division of by If the exact keyword is present, the result value of the sdiv is a poison value if the result would be rounded. The value produced is the floating-point quotient of the two operands. This instruction returns the unsigned integer remainder of a division.

This instruction always performs an unsigned division to get the remainder. Taking the remainder of a division by zero is undefined behavior. This instruction can also take vector versions of the values in which case the elements must be integers.

This instruction returns the remainder of a division where the result is either zero or has the same sign as the dividend, op1 , not the modulo operator where the result is either zero or has the same sign as the divisor, op2 of a value.

For more information about the difference, see The Math Forum. For a table of how this is implemented in various languages, please see Wikipedia: Overflow also leads to undefined behavior; this is a rare case, but can occur, for example, by taking the remainder of a bit division of by The value produced is the floating-point remainder of the two operands.

The remainder has the same sign as the dividend. Bitwise binary operators are used to do various forms of bit-twiddling in a program. They are generally very efficient instructions and can commonly be strength reduced from other instructions.

The resulting value is the same type as its operands. If op2 is statically or dynamically equal to or larger than the number of bits in op1 , this instruction returns a poison value.

If the arguments are vectors, each vector element of op1 is shifted by the corresponding shift amount in op2. If the nuw keyword is present, then the shift produces a poison value if it shifts out any non-zero bits. If the nsw keyword is present, then the shift produces a poison value it shifts out any bits that disagree with the resultant sign bit.

This instruction always performs a logical shift right operation. The most significant bits of the result will be filled with zero bits after the shift. If the exact keyword is present, the result value of the lshr is a poison value if any of the bits shifted out are non-zero.

This instruction always performs an arithmetic shift right operation, The most significant bits of the result will be filled with the sign bit of op1. If the exact keyword is present, the result value of the ashr is a poison value if any of the bits shifted out are non-zero. LLVM supports several instructions to represent vector operations in a target-independent manner.

These instructions cover the element-access and vector-specific operations needed to process vectors effectively. While LLVM does directly support these vector operations, many sophisticated algorithms will want to use target-specific intrinsics to take full advantage of a specific target. The second operand is an index indicating the position from which to extract the element. The index may be a variable of any integer type. The result is a scalar of the same type as the element type of val.

Its value is the value at position idx of val. If idx exceeds the length of val , the results are undefined. The second operand is a scalar value whose type must equal the element type of the first operand. The third operand is an index indicating the position at which to insert the value. The result is a vector of the same type as val. Its element values are those of val except at position idx , where it gets the value elt.

The result of the instruction is a vector whose length is the same as the shuffle mask and whose element type is the same as the element type of the first two operands. The shuffle mask operand is required to be a constant vector with either constant integer or undef values. The elements of the two input vectors are numbered from left to right across both of the vectors.

The shuffle mask operand specifies, for each element of the result vector, which element of the two input vectors the result element gets. If the shuffle mask is undef, the result vector is undef. If any element of the mask operand is undef, that element of the result is undef. If the shuffle mask selects an undef element from one of the input vectors, the resulting element is undef. LLVM supports several instructions for working with aggregate values.

The major differences to getelementptr indexing are:. The second operand is a first-class value to insert. The value to insert must have the same type as the value identified by the indices.

The result is an aggregate of the same type as val. Its value is that of val except that the value at the position specified by the indices is that of elt. A key design point of an SSA-based representation is how it represents memory. This section describes how to read, write, and allocate memory in LLVM. The object is always allocated in the address space for allocas indicated in the datalayout. If a constant alignment is specified, the value result of the allocation is guaranteed to be aligned to at least that boundary.

If not specified, or if zero, the target can choose to align the allocation on any convenient boundary compatible with the type. Memory is allocated; a pointer is returned. The operation is undefined if there is insufficient stack space for the allocation.

When the function returns either with the ret or resume instructions , the memory is reclaimed. Allocating zero bytes is legal, but the result is undefined. The order in which memory is allocated ie. The argument to the load instruction specifies the memory address from which to load. The type specified must be a first class type of known size i. If the load is marked as volatile , then the optimizer is not allowed to modify the number or order of execution of this load with other volatile operations.

Atomic loads produce defined results when they may see multiple atomic stores. The type of the pointee must be an integer, pointer, or floating-point type whose bit width is a power of two greater than or equal to eight and less than or equal to a target-specific size limit.

The optional constant align argument specifies the alignment of the operation that is, the alignment of the memory address. A value of 0 or an omitted align argument means that the operation has the ABI alignment for the target. It is the responsibility of the code emitter to ensure that the alignment information is correct.

Overestimating the alignment results in undefined behavior. Underestimating the alignment may produce less efficient code. An alignment of 1 is always safe. An alignment value higher than the size of the loaded type implies memory up to the alignment value bytes can be safely loaded without trapping in the default address space. The existence of the! The code generator may select special instructions to save cache bandwidth, such as the MOVNT instruction on x If a load instruction tagged with the!

This is analogous to the nonnull attribute on parameters and return values. This metadata can only be applied to loads of a pointer type. The number of bytes known to be dereferenceable is specified by the integer value in the metadata node. The alignment must be a power of 2.

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