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268cfea6bc
use a SUB instruction instead of an ADD, because -128 can be encoded in an 8-bit signed immediate field, while +128 can't be. This avoids the need for a 32-bit immediate field in this case. A similar optimization applies to 64-bit adds with 0x80000000, with the 32-bit signed immediate field. To support this, teach tablegen how to handle 64-bit constants. llvm-svn: 57663
16 lines
362 B
LLVM
16 lines
362 B
LLVM
; RUN: llvm-as < %s | llc -march=x86-64 > %t
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; RUN: not grep add %t
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; RUN: grep subq %t | count 2
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; The immediate can be encoded in a smaller way if the
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; instruction is a sub instead of an add.
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define i64 @foo(i64 inreg %a) nounwind {
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%b = add i64 %a, 2147483648
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ret i64 %b
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}
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define i64 @bar(i64 inreg %a) nounwind {
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%b = add i64 %a, 128
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ret i64 %b
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}
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