From: David Malcolm <dmalcolm@redhat.com>
To: Dibyendu Majumdar <mobile@majumdar.org.uk>
Cc: jit@gcc.gnu.org
Subject: Re: Basic blocks, jump targets and locals
Date: Thu, 01 Jan 2015 00:00:00 -0000 [thread overview]
Message-ID: <1434054685.12727.205.camel@surprise> (raw)
In-Reply-To: <CACXZuxe2GDhN+cPdG4jopq11ZibU6qW5pL==AgahNbEJB1vwoA@mail.gmail.com>
On Thu, 2015-06-11 at 21:26 +0100, Dibyendu Majumdar wrote:
> Hi,
>
> In LLVM the IRBuilder has the concept of a current block where
> instructions are inserted. Reading the libgccjit docs I think that
> there is no notion of current block - i.e. this needs to be maintained
> by the caller - is that correct?
Correct.
> Can one create several blocks in advance - and set a block that is not
> yet inserted into the function as the target for a jump?
Yes. See e.g.:
https://gcc.gnu.org/onlinedocs/jit/intro/tutorial04.html#populating-the-function
which does two passes:
(i) iterates through all of the bytecodes in a function, creating
gcc_jit_block instances for each one
(ii) iterates again, populating the gcc_jit_block instances with
statements
> The scenario
> is this: when compiling Lua bytecode I already know all the jump
> targets. So I pre-create all the basic blocks that relate to the jump
> targets up front - and as each jump is encountered I can easily set
> the jump target to the right block. As and when I cross the bytecode
> that is a jump target the block gets added to the function.
(nods)
> I hope above is clear - if not I can explain by an example.
>
> Can I do something similar with libgccjit?
Hopefully the example above makes it clear.
> Finally - how are local variable related to blocks. In LLVM one has to
> create the local vars in the entry block of the function. Is it the
> same with libgccjit?
Local variables in libgccjit are local to a *function*; there's no
association between them and blocks. Blocks in libgccjit relate to
control flow, not to scope.
Note that any initialization of a local variable has to be done
explicitly, by adding an assignment statement. Typically that
assignment statement would be added to the initial block, as in the
example above (so I suppose that's an association of sorts between
locals and the entry block).
Hope this is clear
Dave
next prev parent reply other threads:[~2015-06-11 20:38 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-01 0:00 Dibyendu Majumdar
2015-01-01 0:00 ` David Malcolm [this message]
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` David Malcolm
2015-01-01 0:00 ` Dibyendu Majumdar
2015-01-01 0:00 ` David Malcolm
2015-01-01 0:00 ` Dibyendu Majumdar
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