Inline assembler in D and LDC, round 2

[Frits van Bommel]

Walter Bright wrote:
> Is the inline assembling actually done by the LLVM back end, or the LDC 
> front end?

The frontend turns it into an GCC-style asm statement (with explicit 
input and output constraints) that shows up as a function literal in the 
IR (only valid as target of a 'call' instruction).

The LLVM codegen then uses those constraints to allocate registers, 
substitutes them in the asm string and emits it directly to the 
assembler as part of the output[1]. (LLVM, like GCC, normally uses an 
external assembler)


[1]: With a few exceptions, IIRC. For example, some part of LLVM turns 
single "bswap"s into an intrinsic llvm.bswap.i<bitsize>() call to help 
analyses, optimizers and the JIT since they don't generally support 
inline asm otherwise.