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    • Dan Gohman's avatar
      Fun x86 encoding tricks: when adding an immediate value of 128, · ca0546fa
      Dan Gohman authored 
      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
      ca0546fa
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