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GH-91719: Make MSVC generate somewhat faster switch code (#91718)

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Apparently a switch on an 8-bit quantity where all cases are
present generates a more efficient jump (doing only one indexed
memory load instead of two).

So we make opcode and use_tracing uint8_t, and generate a macro
full of extra `case NNN:` lines for all unused opcodes.

See https://github.com/faster-cpython/ideas/issues/321#issuecomment-1103263673
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Guido van Rossum 2022-04-21 11:53:57 -07:00 • committed by GitHub
parent d44815cabc
commit f8dc6186d1
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4 changed files with 90 additions and 3 deletions
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7
Tools/scripts/generate_opcode_h.py
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@ -129,6 +129,13 @@ def main(opcode_py, outfile='Include/opcode.h'):
fobj.write("};\n")
fobj.write("#endif\n")
fobj.write("\n")
fobj.write("#define EXTRA_CASES \\\n")
for i, flag in enumerate(used):
if not flag:
fobj.write(f" case {i}: \\\n")
fobj.write(" ;\n")
fobj.write(footer)