[llvm-dev] Support for byte sizes larger than 8 bits
Marek Surovič via llvm-dev
llvm-dev at lists.llvm.org
Mon Aug 17 06:47:33 PDT 2015
lately the company I work for has bumped into a need for a way to
specify a size of byte larger than the regular 8 bits for our targets.
After a bit of research we found out that the feature would require
changes across most of the LLVM framework (including clang) and
maintaining such changes without involving the LLVM devs would be
tedious to say the least.
So my first question would be if such a feature would be welcome in the
LLVM framework. The motivation for implementing the feature is that
certain embedded processors often use custom byte sizes, such as 12
bits, to conserve power while addressing its memory.
The first solution sketch we came up with is to introduce a new field
into the data layout string that would specify the size of a byte (or
char). The default value of the field would be the regular 8 bits. This
way, the information should be propagated through all the necessary
parts of LLVM.
The second issue is how to find and modify the existing code that relies
on the assumption that a byte (or char) in the target is always 8 bits.
The changes we would introduce, should the feature be accepted, would of
course be tested against an existing LLVM target and test-suites to
ensure that we didn't break anything.
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