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When LowerExtract eliminates an EXTRACT_SUBREG with a kill flag, it moves the kill flag to the place where the sub-register is killed. This can accidentally overlap with the use of a sibling sub-register, and we have trouble. In the test case we have this code: Live Ins: %R0 %R1 %R2 %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1 %R2H<def> = LOAD16fi <fi#-1>, 0, Mem:LD(2,4) [FixedStack-1 + 0] %R1L<def> = EXTRACT_SUBREG %R1<kill>, 1 %R0L<def> = EXTRACT_SUBREG %R0<kill>, 1 %R0H<def> = ADD16 %R2H<kill>, %R2L<kill>, %AZ<imp-def>, %AN<imp-def>, %AC0<imp-def>, %V<imp-def>, %VS<imp-def> subreg: CONVERTING: %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1 subreg: eliminated! subreg: killed here: %R0H<def> = ADD16 %R2H, %R2L, %R2<imp-use,kill>, %AZ<imp-def>, %AN<imp-def>, %AC0<imp-def>, %V<imp-def>, %VS<imp-def> The kill flag on %R2 is moved to the last instruction, and the live range overlaps with the definition of %R2H: *** Bad machine code: Redefining a live physical register *** - function: f - basic block: 0x18358c0 (#0) - instruction: %R2H<def> = LOAD16fi <fi#-1>, 0, Mem:LD(2,4) [FixedStack-1 + 0] Register R2H was defined but already live. The fix is to replace EXTRACT_SUBREG with IMPLICIT_DEF instead of eliminating it completely: subreg: CONVERTING: %R2L<def> = EXTRACT_SUBREG %R2<kill>, 1 subreg: replace by: %R2L<def> = IMPLICIT_DEF %R2<kill> Note that these IMPLICIT_DEF instructions survive to the asm output. It is necessary to fix the stack-color-with-reg test case because of that. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78093 91177308-0d34-0410-b5e6-96231b3b80d8
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