I remember hearing years ago from IBM that 64-bit mode programs tended
to run slightly slower than those running in 31-bit mode.
At the time, I assumed the reason was that programs using 8-byte
pointers and integer values use more cache lines and 4K pages/frames
than programs using 4-byte values.
However, in a recent discussion we wondered if perhaps the "grande"
instructions that operate on the full 64-bits of a register might also
run a tiny bit slower than their counterpart instructions that operate
only on the low halves of the registers.
Wondering if anyone can shed some authoritative light on this topic...
--
Phoenix Software International
Edward E. Jaffe
831 Parkview Drive North
El Segundo, CA 90245
https://www.phoenixsoftware.com/
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