Editing Inline assembler (section)

== Motivation and alternatives ==
The embedding of assembly language code is usually done for one of these reasons:<ref name=gcc-dont>{{cite web |title=DontUseInlineAsm |url=https://gcc.gnu.org/wiki/DontUseInlineAsm |website=GCC Wiki |access-date=21 January 2020}}</ref>

* [[Optimization (computer science)|Optimization]]: Programmers can use assembly language code to implement the most performance-sensitive parts of their program's [[algorithm|algorithms]], code that is apt to be more efficient than what might otherwise be generated by the compiler.
* Access to processor-specific [[Instruction (computer science)|instruction]]s: Most processors offer special instructions, such as [[Compare-and-swap|Compare and Swap]] and [[Test-and-set|Test and Set]] instructions which may be used to construct [[Semaphore (programming)|semaphores]] or other synchronization and locking primitives. Nearly every modern processor has these or similar instructions, as they are necessary to implement [[computer multitasking|multitasking]].  Examples of specialized instructions are found in the [[SPARC]] [[Visual Instruction Set|VIS]], [[Intel]] [[MMX (instruction set)|MMX]] and [[Streaming SIMD Extensions|SSE]], and [[Motorola]] [[Altivec]] [[instruction set]]s.
* Access to special [[calling convention]]s not yet supported by the compiler.
* [[System call]]s and interrupts: High-level languages rarely have a direct facility to make arbitrary system calls, so assembly code is used. Direct interrupts are even more rarely supplied.
* To emit special directives for the linker or assembler, for example to change sectioning, macros, or to make symbol aliases.

On the other hand, inline assembler poses a direct problem for the compiler itself as it complicates the analysis of what is done to each variable, a key part of register allocation.<ref>{{cite web |last1=Striegel |first1=Ben |title="To a compiler, a blob of inline assembly is like a slap in the face."|url=https://www.reddit.com/r/rust/comments/eo9pks/the_asm_working_group_has_submitted_their_first/feb7yy4/ |website=Reddit |date=13 January 2020 |access-date=15 January 2020}}</ref> This means the performance might actually decrease. Inline assembler also complicates future porting and maintenance of a program.<ref name=gcc-dont/>

Alternative facilities are often provided as a way to simplify the work for both the compiler and the programmer. [[Intrinsic function]]s for special instructions are provided by most compilers and C-function wrappers for arbitrary system calls are available on every [[Unix]] platform.