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See through aggregates in GVN This PR is extracted from https://github.com/rust-lang/rust/pull/111344 The first 2 commit are cleanups to avoid repeated work. I propose to stop removing useless assignments as part of this pass, and let a later `SimplifyLocals` do it. This makes tests easier to read (among others). The next 3 commits add a constant folding mechanism to the GVN pass, presented in https://github.com/rust-lang/rust/pull/116012. ~This pass is designed to only use global allocations, to avoid any risk of accidental modification of the stored state.~ The following commits implement opportunistic simplifications, in particular: - projections of aggregates: `MyStruct { x: a }.x` gets replaced by `a`, works with enums too; - projections of arrays: `[a, b][0]` becomes `a`; - projections of repeat expressions: `[a; N][x]` becomes `a`; - transform arrays of equal operands into a repeat rvalue. Fixes https://github.com/rust-lang/miri/issues/3090 r? `@oli-obk` |
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