Implement a global value numbering MIR optimization#109597
Merged
bors merged 10 commits intorust-lang:masterfrom Sep 27, 2023
Merged
Implement a global value numbering MIR optimization#109597bors merged 10 commits intorust-lang:masterfrom
bors merged 10 commits intorust-lang:masterfrom
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The aim of this pass is to avoid repeated computations by reusing past assignments. It is based on an analysis of SSA locals, in order to perform a restricted form of common subexpression elimination.
By opportunity, this pass allows for some simplifications by combining assignments. For instance, this pass could be able to see through projections of aggregates to directly reuse the aggregate field (not in this PR).
We handle references by assigning a different "provenance" index to each
Ref/AddressOfrvalue. This ensure that we do not spuriously merge borrows that should not be merged. Meanwhile, we consider all the derefs of an immutable reference to a freeze type to give the same value: