llvm dev - Jan 2011 - [LLVMdev] Increasing TargetRegisterInfo::FirstVirtualRegister?

> If you're interested in doing this, I'd suggest hacking up the
backend to
> not run register allocation, and represent all your "physical"
registers
> are virtual registers.  This gives you an unlimited number.
>
Yes it would be ideal to use all virtual registers, but a glance at the
code seemed to indicate the the use of physical registers, spilling, etc.
was pretty ingrained in all the register allocation algorithms, so it
seemed like it would be difficult to extract.  I also still need to
minimize the number of registers and minimize copies as if it were
generating code for more restrictive hardware.

Ideally I'd like something like the linear register allocator but that
never spilled or assigned physical registers, along with other goodies
like coalescing and phi elimination.

On the other hand, just increasing the allowable physical registers would
immediately solve most of my problems.

Andrew

On Jan 6, 2011, at 10:39 PM, andrew at sidefx.com wrote:
> 
>> If you're interested in doing this, I'd suggest hacking up the
backend to
>> not run register allocation, and represent all your
"physical" registers
>> are virtual registers.  This gives you an unlimited number.
>> 
> 
> Yes it would be ideal to use all virtual registers, but a glance at the
> code seemed to indicate the the use of physical registers, spilling, etc.
> was pretty ingrained in all the register allocation algorithms, so it
> seemed like it would be difficult to extract.  I also still need to
> minimize the number of registers and minimize copies as if it were
> generating code for more restrictive hardware.
> 
> Ideally I'd like something like the linear register allocator but that
> never spilled or assigned physical registers, along with other goodies
> like coalescing and phi elimination.
> 
> On the other hand, just increasing the allowable physical registers would
> immediately solve most of my problems.
Unless your goal is to merge this work onto LLVM mainline, the best thing to do
is a local hack in your tree.

-Chris

hi andrew,


On Fri, Jan 7, 2011 at 2:39 PM,  <andrew at sidefx.com>
wrote:
>
>> If you're interested in doing this, I'd suggest hacking up the
backend to
>> not run register allocation, and represent all your
"physical" registers
>> are virtual registers.  This gives you an unlimited number.
>>
>
> Yes it would be ideal to use all virtual registers, but a glance at the
> code seemed to indicate the the use of physical registers, spilling, etc.
you can override the function "addPassesToEmitFile" of your target
machine, so register allocator will not run on your machinefunctions.

best regards
ether

On 01/07/2011 02:07 AM, Chris Lattner wrote:
>
> Unless your goal is to merge this work onto LLVM mainline, the best thing
to do is a local hack in your tree.
>
> -Chris
Yes, I will create a patch for my tree to increase 
FirstVirtualRegister.  Would this be a good change to include in 2.9?