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r2_3
2005 Apr 20
1
[LLVMdev] adding new instructions to support "swizzle" and "writemask"
...supports swizzle
and writemask.
I have a few solutions:
(1) Treat each channel of a register as a individual SSA variable.
This could generate inefficient machine code.
For example, the instruction:
add r0.xz, r1.y, r2.wx
is translated to two LLVM instructions:
r0_x = add float r1_y, r2_w
r0_z = add float r1_y, r2_x
Subsequent optimization passes could insert other instructions between
these two instruction (for example, in instruction scheduling pass). I
don't know how they could be easily merged back into one instruction.
It could lead to inefficient machine code (though...