Hi Susan,<div><br></div><div>There is some high level documentation about the target independent code generator <a href="http://llvm.org/docs/CodeGenerator.html#register-allocator">here</a>, but it doesn't contain the specifics needed to build an allocator from scratch (e.g, it doesn't describe the issue you just encountered). In my experience the best option has been to just read the existing allocators and see how they work.</div>
<div><br></div><div>If your allocator project yields any documentation on building an LLVM register allocator, patches to our documentation are always welcome. Otherwise, I'll try to find time to distill the lessons from this thread and add them to the target independent code generator document. </div>
<div><br></div><div>Cheers,</div><div>Lang.</div><div class="gmail_extra"><br><br><div class="gmail_quote">On Mon, Dec 3, 2012 at 7:11 AM, Susan Horwitz <span dir="ltr"><<a href="mailto:horwitz@cs.wisc.edu" target="_blank">horwitz@cs.wisc.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<div>Aha, yes, this is definitely helpful!<br>
<br>
Is there documentation on all this somewhere? I still have errors
for some large test inputs, and it would be nice if I didn't have
to keep bugging you for information.<br>
<br>
Thanks!<span class="HOEnZb"><font color="#888888"><br>
<br>
Susan</font></span><div><div class="h5"><br>
<br>
On 12/2/2012 10:55 PM, Lang Hames wrote:<br>
</div></div></div><div><div class="h5">
<blockquote type="cite">
Hi Susan,
<div><br>
</div>
<div>Thanks for the clarification, and the test case. I think I
know what the problem is now. Saving and restoring RBP is the
job of the PEI (PrologEpilogInsertion) pass, which runs after
register allocation. To determine which callee-saved physregs
actually need to be saved it checks
MachineRegisterInfo::isPhysRegOrOverlapUsed(unsigned reg). Your
register allocator needs to notify MachineRegisterInfo about the
physical registers that have been assigned by calling
MachineRegisterInfo::setPhysRegUsed(unsigned reg).</div>
<div><br>
</div>
<div>You only need to call setPhysRegUsed for the physregs that
you actually use. You do not need to specify the aliasing
registers.</div>
<div><br>
</div>
<div>Hope this helps!</div>
<div><br>
</div>
<div>Regards,</div>
<div>Lang.</div>
<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">On Sat, Dec 1, 2012 at 9:31 AM, Susan
Horwitz <span dir="ltr"><<a href="mailto:horwitz@cs.wisc.edu" target="_blank">horwitz@cs.wisc.edu</a>></span>
wrote:<br>
<blockquote class="gmail_quote">
<div>
<div>
<div>On 11/30/2012 6:36 PM, Lang Hames wrote:<br>
</div>
<blockquote type="cite"> <br>
<div><br>
</div>
<div>RBP is used as the frame pointer on x86 (hence
its automatic appearance in your code), and
shouldn't be allocated to any vreg in function bar.
Loading/saving RBP should be managed by the stack
frame setup/teardown code.</div>
</blockquote>
<blockquote type="cite">
<div>If it doesn't already, your allocator should
filter out reserved registers (See
MachineRegisterInfo::isReserved(unsigned preg)) when
assigning physregs.</div>
</blockquote>
<br>
</div>
I AM filtering out reserved registers. <br>
<br>
I am not allocating RBP in function bar, I am allocating
EBP, because it is NOT in the list of reserved registers
for function bar.<br>
<br>
Neither register RBP nor register EBP is saved/restored
across the call from foo to bar, either by the code for
the call or the code for entry to bar.<br>
<br>
The input C file that is causing this problem is flex.c
(attached). The calling function is "yyparse" and the
called function is "scinstal".<br>
<br>
Here are the reserved registers for yyparse: { 7 44 54 106
111 114 118 }<br>
<br>
Here are the reserved registers for scinstal: { 54 111 114
}<br>
<br>
Register EBP is preg 44, which is NOT in the reserved list
for scinstal (nor is it an alias of any of those reserved
registers; the aliases are { <a href="tel:50%2064%20117%20118" value="+15064117118" target="_blank">50 64 117 118</a> }). I don;t know
which preg corresponds to RBP.<br>
<br>
You say that RBP should be saved/restored across the
call. I tried to generate that code, but, as I said in my
previous mail, I don't know how to get the appropriate
TargetRegisterClass (needed to call
CreateSpillStackObject). Should I instead be generating
code to save register EBP at the start of scinstal,
restoring it at the end of that function?<span><br>
<br>
Susan</span>
<div><br>
<br>
<blockquote type="cite">
<div><br>
</div>
<div><span>ArrayRef<MCPhysReg> pregs =
TRC->getRawAllocationOrder(&MF);</span></div>
<div><span>for (int i = 0; i < pregs.size(); ++i) {</span></div>
<div><span> if (MRI->isReserved(pregs[i]))</span></div>
<div><span> continue;</span></div>
<div><span> // use preg...</span></div>
<div><span>}</span></div>
<div><br>
</div>
<div>You could also use the AllocationOrder class to
simplify the task of finding valid pregs, though it
does require you to use VirtRegMap. </div>
<div><br>
</div>
<div>If you are already checking the reserved regs
then I've misdiagnosed the problem. I'd be happy to
dig further if you can point me to a copy of your
allocator and a test case.</div>
<div><br>
</div>
<div>Cheers,</div>
<div>Lang.</div>
<div class="gmail_extra"><br>
<br>
<div class="gmail_quote">On Thu, Nov 29, 2012 at
3:49 PM, Susan Horwitz <span dir="ltr"><<a href="mailto:horwitz@cs.wisc.edu" target="_blank">horwitz@cs.wisc.edu</a>></span>
wrote:<br>
<blockquote class="gmail_quote">I have a new
problem: Register RBP is used in a function foo.
(I am not allocating RBP to any virtual
register, the instances of RBP in function foo
are in the machine code when my register
allocator starts.)<br>
<br>
Function foo calls function bar. Register RBP
is not saved across the call, though it is live
after the call. Function bar includes a virtual
register. The code that I'm using to find the
registers available to be allocated to that
virtual register includes EBP in that
available-preg set. This is a disaster, since
writing into EBP clobbers RBP.<br>
<br>
I tried to add code to save all live physical
registers across calls, but I don't know how to
get the appropriate TargetRegisterClass (needed
to call CreateSpillStackObject).<br>
<br>
Is there a different way to save/restore RBP
across calls? Or a way to get its
TargetRegisterClass?<span><br>
<br>
Susan<br>
</span></blockquote>
</div>
<br>
</div>
</blockquote>
<br>
</div>
</div>
</blockquote>
</div>
<br>
</div>
</blockquote>
<br>
</div></div></div>
</blockquote></div><br></div>