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Commit 527ca7e2 authored by Dan Gohman's avatar Dan Gohman
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Re-enable elimination of unnecessary SUBREG_TO_REG instructions in 

LowerSubregs, and fix an x86-64 isel bug that this exposed.

SUBREG_TO_REG for x86-64 implicit zero extension is only safe for
isel to generate when the source is known to always have zeros in
the high 32 bits. The EXTRACT_SUBREG instruction does not clear
the high 32 bits.

llvm-svn: 54444
parent a8dbaeb1
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