66 lines
1.5 KiB
Factor
66 lines
1.5 KiB
Factor
USING: compiler.cfg.instructions help.markup help.syntax kernel ;
|
|
IN: compiler.cfg.alias-analysis
|
|
|
|
HELP: useless-compare?
|
|
{ $values
|
|
{ "insn" "a " { $link ##compare } " instruction" }
|
|
{ "?" boolean }
|
|
}
|
|
{ $description "Checks if the comparison instruction is required." } ;
|
|
|
|
ARTICLE: "compiler.cfg.alias-analysis"
|
|
"Alias analysis for stack operations, array elements and tuple slots"
|
|
"We try to eliminate redundant slot operations using some simple heuristics."
|
|
$nl
|
|
"All heap-allocated objects which are loaded from the stack, or other object slots are pessimistically assumed to belong to the same alias class."
|
|
$nl
|
|
"Freshly-allocated objects get their own alias class."
|
|
$nl
|
|
"Simple pseudo-C example showing load elimination:"
|
|
{ $code
|
|
"int *x, *y, z: inputs"
|
|
"int a, b, c, d, e: locals"
|
|
}
|
|
"Before alias analysis:"
|
|
{ $code
|
|
"a = x[2]"
|
|
"b = x[2]"
|
|
"c = x[3]"
|
|
"y[2] = z"
|
|
"d = x[2]"
|
|
"e = y[2]"
|
|
"f = x[3]"
|
|
}
|
|
"After alias analysis:"
|
|
{ $code
|
|
"a = x[2]"
|
|
"b = a /* ELIMINATED */"
|
|
"c = x[3]"
|
|
"y[2] = z"
|
|
"d = x[2] /* if x=y, d=z, if x!=y, d=b; NOT ELIMINATED */"
|
|
"e = z /* ELIMINATED */"
|
|
"f = c /* ELIMINATED */"
|
|
}
|
|
"Simple pseudo-C example showing store elimination:"
|
|
$nl
|
|
"Before alias analysis:"
|
|
{ $code
|
|
"x[0] = a"
|
|
"b = x[n]"
|
|
"x[0] = c"
|
|
"x[1] = d"
|
|
"e = x[0]"
|
|
"x[1] = c"
|
|
}
|
|
"After alias analysis:"
|
|
{ $code
|
|
"x[0] = a /* dead if n = 0, live otherwise; NOT ELIMINATED */"
|
|
"b = x[n]"
|
|
"x[0] = c"
|
|
"/* x[1] = d */ /* ELIMINATED */"
|
|
"e = c"
|
|
"x[1] = c"
|
|
} ;
|
|
|
|
ABOUT: "compiler.cfg.alias-analysis"
|