C++: Make IR generation robust against functions with many declaring types #15316
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鈥ore than 10 types. If it has more than 10 types we generate an unknown type.
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When we merged #12125 we started seeing a few (templated) member functions with many 1000s of (templated) declaring types.
We use the type of the declaring function to infer the result type of a write side effect on the qualifier of a member function call. And when there are
Ndeclaring types for a member function call, the write side effect hasNresult types 馃槺. This causes massive slowdowns in the IR alias analysis.This PR changes the IR generation of these write side effect instructions so that we return an "unknown type" rather than a large number of types if we're ever in a situation where there are more than 10 declaring types.
I picked 10 rather arbitrarily as the project I was testing this on had cases where there were 6 declaring types even before we merged #12125.
I haven't been able to reproduce this in a test, but on a project that exhibited this performance problem I'm seeing a difference in the output of PrintIR: https://www.diffchecker.com/CQ6UH8IN/