[LLVMdev] Being able to know the jitted code-size before emitting
sabre at nondot.org
Fri Apr 4 13:07:58 PDT 2008
On Fri, 4 Apr 2008, Jonathan S. Shapiro wrote:
> Evan: please explain how span-dependent branches are resolved in your
> method. You don't need to compute the bits that will be emitted, but you
> do need to compute the length of those bits. In most real
> implementations, the two steps are therefore inseparable.
I think the important point here is that llvm explicitly represent short
and long branches as two different instructions. We don't leave it up to
the assembler to determine whether a short or long branch is to be used.
The PPC and ARM backend have branch shortening passes to know what sort of
branch to us, for example.
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