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When a virtual register has a single value that is defined as a copy of a reserved register, permit that copy to be joined. These virtual register are usually copies of the stack pointer: %vreg75<def> = COPY %ESP; GR32:%vreg75 MOV32mr %vreg75, 1, %noreg, 0, %noreg, %vreg74<kill> MOV32mi %vreg75, 1, %noreg, 8, %noreg, 0 MOV32mi %vreg75<kill>, 1, %noreg, 4, %noreg, 0 CALLpcrel32 ... Coalescing these virtual registers early decreases register pressure. Previously, they were coalesced by RALinScan::attemptTrivialCoalescing after register allocation was completed. The lower register pressure causes the mcinst-lowering-cmp0.ll test case to fail because it depends on linear scan spilling a particular register. I am deleting 2008-08-05-SpillerBug.ll because it is counting the number of instructions emitted, and its revision history shows the 'correct' count being edited many times. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128845 91177308-0d34-0410-b5e6-96231b3b80d8
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