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New semantics for the integer 'for' loop

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The numerical 'for' loop over integers now uses a precomputed counter
to control its number of iteractions. This change eliminates several
weird cases caused by overflows (wrap-around) in the control variable.
(It also ensures that every integer loop halts.)

Also, the special opcodes for the usual case of step==1 were removed.
(The new code is already somewhat complex for the usual case,
but efficient.)
This commit is contained in:
Roberto Ierusalimschy 2019-03-19 10:53:18 -03:00
parent 1e0c73d5b6
commit 9b37a4695e
10 changed files with 213 additions and 185 deletions
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4
testes/code.lua
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@ -303,9 +303,9 @@ check(function (x) return x & 2.0 end, 'LOADF', 'BAND', 'RETURN1')
-- basic 'for' loops
check(function () for i = -10, 10.5 do end end,
'LOADI', 'LOADK', 'LOADI', 'FORPREP1', 'FORLOOP1', 'RETURN0')
'LOADI', 'LOADK', 'LOADI', 'FORPREP', 'FORLOOP', 'RETURN0')
check(function () for i = 0xfffffff, 10.0, 1 do end end,
'LOADK', 'LOADF', 'LOADI', 'FORPREP1', 'FORLOOP1', 'RETURN0')
'LOADK', 'LOADF', 'LOADI', 'FORPREP', 'FORLOOP', 'RETURN0')
-- bug in constant folding for 5.1
check(function () return -nil end, 'LOADNIL', 'UNM', 'RETURN1')