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08762f9f1e
An identity COPY like this: %AL = COPY %AL, %EAX<imp-def> has no semantic effect, but encodes liveness information: Further users of %EAX only depend on this instruction even though it does not define the full register. Replace the COPY with a KILL instruction in those cases to maintain this liveness information. (This reverts a small part of r238588 but this time adds a comment explaining why a KILL instruction is useful). llvm-svn: 274952
36 lines
800 B
LLVM
36 lines
800 B
LLVM
; RUN: llc < %s -mtriple=i686-unknown-linux-gnu | FileCheck %s -check-prefix=X86
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; RUN: llc < %s -mtriple=x86_64-unknown-linux-gnu | FileCheck %s -check-prefix=X64
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; RUN: llc < %s -mtriple=x86_64-linux-gnux32 | FileCheck %s -check-prefix=X32
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define zeroext i8 @foo() nounwind ssp {
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entry:
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%0 = tail call zeroext i16 (...) @bar() nounwind
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%1 = lshr i16 %0, 8
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%2 = trunc i16 %1 to i8
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ret i8 %2
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; X86-LABEL: foo
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; X86: calll
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; X86-NEXT: movb %ah, %al
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; X86-NEXT: addl $12, %esp
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; X86-NEXT: retl
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; X64-LABEL: foo
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; X64: callq
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; X64-NEXT: # kill
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; X64-NEXT: shrl $8, %eax
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; X64-NEXT: # kill
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; X64-NEXT: popq
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; X64-NEXT: retq
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; X32-LABEL: foo
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; X32: callq
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; X32-NEXT: # kill
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; X32-NEXT: shrl $8, %eax
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; X32-NEXT: # kill
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; X32-NEXT: popq
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; X32-NEXT: retq
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}
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declare zeroext i16 @bar(...)
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