llvm dev - Jun 2009 - [LLVMdev] making trampolines more portable

I'm not sure whether there are any other cases where using LLVM requires 
knowledge of the target architecture, but needing it for trampolines is 
worrying me.  I'm putting together things where the program that's 
generating the LLVM intermediate code doesn't have any way to know what 
the target architecture will be.

Right now I'm using alloca to get a block that is expected to be more 
than large enough, and assuming that align 4 will work.  Any chance of 
LLVM gaining a new intrinsic that returns the appropriate size and 
alignment for the target?  (Might need the alloca() instruction extended 
or a new version to support non-constant alignment?)

Thanks!
Eric

On Sat, Jun 13, 2009 at 6:59 PM, Eric Smith<eric at brouhaha.com>
wrote:
> Right now I'm using alloca to get a block that is expected to be more
> than large enough, and assuming that align 4 will work.  Any chance of
> LLVM gaining a new intrinsic that returns the appropriate size and
> alignment for the target?  (Might need the alloca() instruction extended
> or a new version to support non-constant alignment?)
The alignment is easy: just allocate as an array of pointers, and I'm
pretty sure you'll get appropriate alignment for every architecture.
Also, for lack of an intrinsic, there's a relatively easy workaround:
you can declare a global containing the correct size, then link in a
small target-specific .bc with the definition right before code
generation.

-Eli