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RangeAnalysis: Improve bounds that rely on relative modulus. #14664

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Merged
merged 2 commits into from
Nov 3, 2023
Merged

RangeAnalysis: Improve bounds that rely on relative modulus. #14664

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7bf271f
RangeAnalysis: Improve bounds that rely on relative modulus.
aschackmull Nov 2, 2023
f2b5265
Rangeanalysis: Filter useless modulo results.
aschackmull Nov 2, 2023
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10 changes: 4 additions & 6 deletions cpp/ql/test/library-tests/ir/range-analysis/SimpleRangeAnalysis_tests.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1077,9 +1077,8 @@ void mask_at_start(int len) {
}
// Do something with leftOver
for (int index = leftOver; index < len; index+=64) {
range(index); // $ range="<=InitializeParameter: len-1"
// This should be in bounds
range(index + 16); // $ range="<=InitializeParameter: len+15" range="==Phi: index+16" MISSING: range="<=InitializeParameter: len-1"
range(index); // $ range="<=InitializeParameter: len-64" range=">=Store: ... & ... | Store: leftOver+0"
range(index + 63); // $ range="<=InitializeParameter: len-1" range="==Phi: index+63" range=">=Store: ... & ... | Store: leftOver+63"
}
}

Expand All @@ -1095,8 +1094,7 @@ void mod_at_start(int len) {
}
// Do something with leftOver
for (int index = leftOver; index < len; index+=64) {
range(index); // $ range="<=InitializeParameter: len-1"
// This should be in bounds
range(index + 16); // $ range="<=InitializeParameter: len+15" range="==Phi: index+16" MISSING: range="<=InitializeParameter: len-49"
range(index); // $ range="<=InitializeParameter: len-64" range=">=Store: ... % ... | Store: leftOver+0"
range(index + 63); // $ range="<=InitializeParameter: len-1" range="==Phi: index+63" range=">=Store: ... % ... | Store: leftOver+63"
}
}
8 changes: 8 additions & 0 deletions shared/rangeanalysis/codeql/rangeanalysis/ModulusAnalysis.qll
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Original file line number Diff line number Diff line change
Expand Up @@ -264,6 +264,14 @@ module ModulusAnalysis<
val = remainder(val0 + delta, mod)
)
or
exists(Sem::Expr mid, int v, int m1, int m2 |
exprModulus(mid, b, v, m1) and
e = modExpr(mid, m2) and
mod = m1.gcd(m2) and
mod != 1 and
val = remainder(v, mod)
)
or
exists(Sem::ConditionalExpr cond, int v1, int v2, int m1, int m2 |
cond = e and
condExprBranchModulus(cond, true, b, v1, m1) and
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