[LLVMdev] Bug? Coalescing & Updating Subreg Intervals

[David Greene]

On Thursday 21 February 2008 10:53, David Greene wrote:

> Why do we do this trimming?  The comment seems to say we don't care about
> the rest of the live range from Clobbers (%reg1026 in this case) but that
> doesn't match with our expectation that %reg15 will contain all of the live
> range information from %reg1026.

I'll add that merging this correctly could get tricky.  %reg15 contains the
following live ranges, all of which overlap  [458,5168:0 [0]) from %reg1026:

[938,942:1 [0])[942,943:2 [0])[962,966:3 [0])[966,967:4 [0])[1242,1246:5 [0])
[1246,1247:6 [0])[1266,1270:7 [0])[1270,1271:8 [0])[1578,1582:9 [0])
[1582,1583:10 [0])[1602,1606:11 [0])[1606,1607:12 [0])[2314,2318:13 [0])
[2318,2319:14 [0])[2338,2342:15 [0])[2342,2343:16 [0])[3366,3370:17 [0])
[3370,3371:18 [0])[3390,3394:19 [0])[3394,3395:20 [0])[3642,3646:21 [0])
[3646,3647:22 [0])[3666,3670:23 [0])[3670,3671:24 [0])[3942,3946:25 [0])
[3946,3947:26 [0])[3966,3970:27 [0])[3970,3971:28 [0])

They all have different value numbers.  How should this get merged in this 
case?  Do we process each of these live ranges against  [458,5168:0 [0])
using the existing code?

What do we do with the holes between them?  Fill them with new ranges
that have an unknown definition value?

                                                     -Dave