[LLVMdev] X86TargetLowering::LowerToBT

[Chris Sears]

The problem is that REX TEST reg,#(1<<37) is 10 bytes vs 5 bytes for REX BT
reg,37.
That's a large space penalty to pay for a possible partial update stall.

So the idea of generating BT for -Os and TEST for -Ofast makes sense to me.
Regardless, LowerToBT is generating TEST for small values.

I'm still tracking down the Clang issue and I'd like folks to look at that.
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