[LLVMbugs] [Bug 13608] New: Need an alternative register allocation order

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Tue Aug 14 14:44:06 PDT 2012


             Bug #: 13608
           Summary: Need an alternative register allocation order
           Product: new-bugs
           Version: trunk
          Platform: PC
        OS/Version: Windows NT
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: weimingz at codeaurora.org
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Currently, LLVM allocates registers in a linear order: given a VR, it tries all
the regs in the corresponding Reg Class in the same order.
In many cases, it is desirable as it can minimize register pressure.

However, on some ARM processor with limited register renaming capability, we
observe performance loss due to increased false data dependency.

So, we suggest to add an optional round-robin style register allocation
ordering, which can be enabled on-demand.

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