[llvm-bugs] [Bug 27331] New: LiveRange not updated correctly in RegisterCoalescer

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=27331

            Bug ID: 27331
           Summary: LiveRange not updated correctly in RegisterCoalescer
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Register Allocator
          Assignee: unassignedbugs at nondot.org
          Reporter: tstellar at gmail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Created attachment 16213
  --> https://llvm.org/bugs/attachment.cgi?id=16213&action=edit
Failing test case

Compiling the attached test case results in a verifier error.  Command ot
reproduce:

llc -mtriple=amdgcn--amdhsa -mcpu=fiji coalescer-bug.ll -verify-machineinstrs
-o - 

qcolombet helped be debug this on IRC, and it appears the problem is that the
live range information is not updated correctly during this transformation:

**BEFORE**
%vreg23 = 0
%vreg24:sub0 = %vreg23
%vreg24:sub1 = 2146435072
USE %vreg24
%vreg80:sub0 = %vreg23
%vreg80:sub1 = 1076494336
USE %vreg80

**AFTER**

%vreg80:sub0 = 0
%vreg80:sub1 = 2146435072
USE %vreg80
%vreg80:sub1 = 1076494336
USE %vreg80

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