Tim Northover 18f68f6d1a ARM64: use 32-bit moves for constants where possible. ...

If we know that a particular 64-bit constant has all high bits zero, then we
can rely on the fact that 32-bit ARM64 instructions automatically zero out the
high bits of an x-register. This gives the expansion logic less constraints to
satisfy and so sometimes allows it to pick better sequences.

Came up while porting test/CodeGen/AArch64/movw-consts.ll: this will allow a
32-bit MOVN to be used in @test8 soon.

llvm-svn: 206379

2014-04-16 11:52:51 +00:00

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