InlineAssembler

InlineAssembler is a facility in many programming languages that allows embedding small blocks of assembly language within standard source code. It is commonly used to access processor-specific instructions, perform low-level control, or implement micro-optimizations when high-level code cannot express the required behavior.

In languages such as C and C++, inline assembly is provided by compilers (for example, GCC/Clang) and permits a direct assembly fragment to be inserted in a function. The fragment can declare input and output operands and a list of clobbered registers or memory, informing the compiler about which resources are read, written, or affected beyond the declared operands. The assembler block can be marked volatile to prevent the compiler from reordering or removing it during optimization.

InlineAssembler ties code to a particular architecture and calling convention, reducing portability and increasing maintenance cost. It may complicate debugging and hinder future compiler optimizations. Developers should use it sparingly, preferring intrinsics or intrinsic functions when available, and isolating assembly in small, well-documented sections.

Architectural specifics vary: GCC-style extended inline assembly uses operands, constraints, and clobbers; MSVC provides an older __asm syntax limited to 32-bit targets, with modern compilers encouraging separate assembly files or intrinsics. Cross-language portability is generally limited, and code should be guarded by architecture checks.

Examples of use include implementing memory barriers, lock-free primitives, or exploiting specialized instructions (SSE, NEON, or bit-manipulation instructions) not exposed by the compiler optimizations.