llvm dev - Jul 2004 - [LLVMdev] Moving between registers of different classes

Suppose I need to align an address register to even boundary. Since address 
register can't be AND-ed with anything, I move the value into general
purpose
register, to "and" and then move it into address register.
Unfortunately, the
register allocator crashes. Here's machine code:

        %reg1030 = - %reg1027, 1
        %reg1031 = move %reg1030
        %reg1032 = + %reg1031, -2
        %reg1033 = move %reg1032
        %ar1 = load64 %gr1<def>, %reg1033

and here's assertion:

llc: LiveIntervals.cpp:507: void llvm::LiveIntervals::joinIntervals(): 
Assertion `rcA == rcB && "registers must be of the same
class"' failed.
(gdb) up 4
.....
(gdb) p *intA
$1 = (llvm::LiveInterval &) @0x8064698: {reg = 1030, weight = 0,
........
(gdb) p *intB
$2 = (llvm::LiveInterval &) @0x80646b8: {reg = 1031, weight = 0,
.......

Is there anything I can do to make it work? Actually, it seems like a bug in 
register allocator. If it can't coalesce intervals because there are 
different register classes, it should just leave the move alone, not crash.

- Volodya

On Tue, 2004-07-06 at 09:41, Vladimir Prus wrote:
> Is there anything I can do to make it work? Actually, it seems like a bug
in
> register allocator. If it can't coalesce intervals because there are 
> different register classes, it should just leave the move alone, not crash.
You are right, it shouldn't crash. The assert was added to check if the
x86 instructor selector ever did a move between two different register
classes and it was left there. Can you try the attached patch and let me
know if it works?

-- 

Alkis
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