[Python-Dev] new bytecode results (original) (raw)

M.-A. Lemburg mal@lemburg.com
Fri, 28 Feb 2003 09:41:29 +0100

Andrew McNamara wrote:

The general problem with the ceval switch statement is that it is too big. Adding new opcodes will only make it bigger, so I doubt that much can be gained in general by trying to come up with new do-everything-in-one-opcode cases. [...]

The last point is probably compiler dependent. GCC has the tendency to use the same layout for the assembler code as you use in the C source code, so placing often used code close to the top results in better locality (at least on my machines). My experience with gcc (on x86) is that it uses a lookup table for contiguous switch statements rather than a long chain of compares/branches. A quick look at the assembler output from ceval.c suggests it's using a lookup table.

Right, but the code for the case implementations itself is ordered (more or less) in the order you use in the C file. At least that was the case at the time (which must have been GCC 2.95.x or even earlier).

What architecture did you observe this on?

Linux.

-- Marc-Andre Lemburg eGenix.com

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