Increased Elimination of Dependencies
The most common method used to zero a register is to exclusive-OR it with itself. This method is favored because it reduces code size. However, the instruction is dependent on the register's previous contents.
Earlier versions of the Pentium® 4 processor detected when the XOR, PXOR, and SUB instructions were used to zero a register and they removed the dependency on the source register. The 90nm Pentium® 4 detects additional instructions when they are used in the same manner (e.g., the SSE instruction XORPS and the SSE2 PSUB and XORPD instructions).
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