Should we ever stabilize inline assembly?

language design
14

A minimal implementation of asm! is actually not that complicated since 90% of the work can be offloaded by invoking the system assembler. Here's a rough outline of how it could work:

  1. Run register allocation on the asm fragment, using the constraints specified in the asm!. You may need to extend your compiler's register allocator to support this.

  2. Perform string substitution to replace the placeholders with actual register names.

  3. Generate an external asm file with the following contents (replace ${ID} with some unique identifier):

.section .text.inline_asm_${ID},"ax",@progbits
.globl inline_asm_${ID}
.type inline_asm_${ID}, @function
inline_asm_${ID}:
    /* <insert asm string here with registers filled in> */
    jmp inline_asm_${ID}_return
.size inline_asm_${ID}, . - inline_asm_${ID}
  1. For the actual code generation of the asm! in your compiler, just emit a jump to the external asm block, and a label for the external asm to return to:
// ...
   jmp inline_asm_${ID}
.globl inline_asm_${ID}_return
inline_asm_${ID}_return:
// ...
  1. Assemble and link in the generated extern asm files.
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