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c4c59192e6
We never need to access entries from these maps outside of the current basic block. This could only ever become a consideration when flow control happens inside a full-expression (i.e. we have multiple basic blocks for a full expression); there are two kinds of expression where this can happen, but we already deal with these in other ways: * Short-circuiting logical operators (`&&` and `||`) have operands that live in different basic blocks than the operator itself, but we already have code in the framework to retrieve the value of these operands from the environment for the block they are computed in, rather than in the environment of the block containing the operator. * The conditional operator similarly has operands that live in different basic blocks. However, we currently don't implement a transfer function for the conditional operator. When we do this, we need to retrieve the values of the operands from the environments of the basic blocks they live in, as we already do for logical operators. This patch adds a comment to this effect to the code. Clearing out `ExprToLoc` and `ExprToVal` has two benefits: * We avoid performing joins on boolean expressions contained in `ExprToVal` and hence extending the flow condition in cases where this is not needed. Simpler flow conditions should reduce the amount of work we do in the SAT solver. * Debugging becomes easier when flow conditions are simpler and `ExprToLoc` / `ExprToVal` don’t contain any extraneous entries. Benchmark results on Crubit's `pointer_nullability_analysis_benchmark show a slight runtime increase for simple benchmarks, offset by substantial runtime reductions for more complex benchmarks: ``` name old cpu/op new cpu/op delta BM_PointerAnalysisCopyPointer 29.8µs ± 1% 29.9µs ± 4% ~ (p=0.879 n=46+49) BM_PointerAnalysisIntLoop 101µs ± 3% 104µs ± 4% +2.96% (p=0.000 n=55+57) BM_PointerAnalysisPointerLoop 378µs ± 3% 245µs ± 3% -35.09% (p=0.000 n=47+55) BM_PointerAnalysisBranch 118µs ± 2% 122µs ± 3% +3.37% (p=0.000 n=59+59) BM_PointerAnalysisLoopAndBranch 779µs ± 3% 413µs ± 5% -47.01% (p=0.000 n=56+45) BM_PointerAnalysisTwoLoops 187µs ± 3% 192µs ± 5% +2.80% (p=0.000 n=57+58) BM_PointerAnalysisJoinFilePath 17.4ms ± 3% 7.2ms ± 3% -58.75% (p=0.000 n=58+57) BM_PointerAnalysisCallInLoop 14.7ms ± 4% 10.3ms ± 2% -29.87% (p=0.000 n=56+58) ```