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Author SHA1 Message Date
Ahmed Bougacha 12eb558bd9 [X86] 8bit divrem: Improve codegen for AH register extraction.
For 8-bit divrems where the remainder is used, we used to generate:
    divb  %sil
    shrw  $8, %ax
    movzbl  %al, %eax

That was to avoid an H-reg access, which is problematic mainly because
it isn't possible in REX-prefixed instructions.

This patch optimizes that to:
    divb  %sil
    movzbl  %ah, %eax

To do that, we explicitly extend AH, and extract the L-subreg in the
resulting register.  The extension is done using the NOREX variants of
MOVZX.  To support signed operations, MOVSX_NOREX is also added.
Further, this introduces a new SDNode type, [us]divrem_ext_hreg, which is
then lowered to a sequence containing a single zext (rather than 2).

Differential Revision: http://reviews.llvm.org/D6064

llvm-svn: 221176
2014-11-03 20:26:35 +00:00