[LLVMdev] Proposal: Adding aligned instruction bundle support to MC

[Eli Bendersky]

> How will these bundles interact with ARM codegen? The constant island pass in particular.
>

Hi Jim,

This is a great question.
>From the compiler's point of view, these bundles indeed pose a problem
for the constant island pass. At this point for the NaCl platform we
disable this pass, generating instructions like movt instead (NaCl
requires at least v7 for ARM). However, as a future enhancement we'd
like to follow gcc's path and adjust the pass to coexist with
potential bundling by computing worst-case estimates for the sizes of
bundle-locked instruction sequences.

>From the assembler's point of view, assembly code that refers to data
using labels should generate errors in the event that these labels
become too too far to reach, similarly to the current situation in
gas.

Eli