Use only_bind_out to force a good join order.#5851
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hvitved
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May 7, 2021
| result.getUnboundDeclaration() = | ||
| this.getASubsumedStaticTarget0(Gvn::getGlobalValueNumber(result.getDeclaringType())) | ||
| this.getASubsumedStaticTarget0(pragma[only_bind_out](Gvn::getGlobalValueNumber(result | ||
| .getDeclaringType()))) |
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How about instead changing
cached
GvnType getGlobalValueNumber(Type t) { ... }to
cached
GvnType getGlobalValueNumberImpl(Type t) { ... }
pragma[inline]
GvnType getGlobalValueNumber(Type t) {
result = pragma[only_bind_out](getGlobalValueNumberImpl(t))
}in Unification.qll?
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That seems to break other code. Specifically typeConstraintUnifiable/typeConstraintSubsumes in Unification.qll where we rely on doing getGlobalValueNumber backwards and forcing the optimiser not to do that makes the code awful. It looks we avoid blowup in those cases due to how small TTypeConstraint is.
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OK, let's get this in now, and then I can investigate the other approach in a follow-up PR.
hvitved
approved these changes
May 18, 2021
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This predicate changes to a bad join order with slight changes in the optimiser. By adding a
pragmahere we make it so that we avoid usingGvn::getGlobalValueNumberbackwards where possible.This makes it easier to make future optimiser changes which don't break this predicate.