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function livein's. Take 2008-03-10-RegAllocInfLoop.ll, the schedule looks like this after these copies are inserted:
entry: 0x12049d0, LLVM BB @0x1201fd0, ID#0:
Live Ins: %EAX %EDX %ECX
%reg1031<def> = MOVPC32r 0
%reg1032<def> = ADD32ri %reg1031, <es:_GLOBAL_OFFSET_TABLE_>, %EFLAGS<imp-def>
%reg1028<def> = MOV32rr %EAX
%reg1029<def> = MOV32rr %EDX
%reg1030<def> = MOV32rr %ECX
%reg1027<def> = MOV8rm %reg0, 1, %reg0, 0, Mem:LD(1,1) [0x1201910 + 0]
%reg1025<def> = MOV32rr %reg1029
%reg1026<def> = MOV32rr %reg1030
%reg1024<def> = MOV32rr %reg1028
The copies unnecessarily increase register pressure and it will end up requiring a physical register to be spilled.
With -schedule-livein-copies:
entry: 0x12049d0, LLVM BB @0x1201fa0, ID#0:
Live Ins: %EAX %EDX %ECX
%reg1031<def> = MOVPC32r 0
%reg1032<def> = ADD32ri %reg1031, <es:_GLOBAL_OFFSET_TABLE_>, %EFLAGS<imp-def>
%reg1024<def> = MOV32rr %EAX
%reg1025<def> = MOV32rr %EDX
%reg1026<def> = MOV32rr %ECX
%reg1027<def> = MOV8rm %reg0, 1, %reg0, 0, Mem:LD(1,1) [0x12018e0 + 0]
Much better!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48307 91177308-0d34-0410-b5e6-96231b3b80d8
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