[LLVMbugs] [Bug 15264] New: RegisterCoalescer should do more subregister remats

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=15264

            Bug ID: 15264
           Summary: RegisterCoalescer should do more subregister remats
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Register Allocator
          Assignee: unassignedbugs at nondot.org
          Reporter: zwarich at apple.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

It should be possible to remat this pair of instructions:

DefMI: %vreg11<def> = MOV16r0 %EFLAGS<imp-def,dead>; GR16:%vreg11
CopyMI: %vreg23:sub_16bit<def,read-undef> = COPY %vreg11; GR32:%vreg23
NewMI: %vreg23:sub_16bit<def,read-undef> = MOV16r0 %EFLAGS<imp-def,dead>;
GR32:%vreg23

However, reMaterializeTrivialDef() currently bails because GR32 != GR16.

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