[LLVMbugs] [Bug 4273] New: Top-down list schedulers do not support physreg dependencies

bugzilla-daemon at cs.uiuc.edu bugzilla-daemon at cs.uiuc.edu
Tue May 26 23:32:56 PDT 2009


           Summary: Top-down list schedulers do not support physreg
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Common Code Generator Code
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: asl at math.spbu.ru
                CC: llvmbugs at cs.uiuc.edu

Currently when scheduling for latency (and thus - via topdown list schedulers)
I need to always flag comparison to conditional branch since it's impossible to
reuse the status register due to lack of physreg dependencies.

This is quite unfortunate and yields ugly code :(

I think one can easily reproduce the problem with x86 backend codegen'ing
something like select_cc / br_cc and changing default (pre-RA) scheduler to

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