Backport IMDCE improvements into firtool 1.37 #5318
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Close #4867 This improves IMDCE by managing instance liveness per instance (previously if there exists an alive instance, it affected all other instances). As we cannot delete modules with side effects (e.g. print/assert/cover) even when they don't have arguments, `undeletableBlocks` keeps tracks of modules we cannot delete. ```scala circuit Top: module PassThrough: input a: UInt<1> output b: UInt<1> b <= a module Top: input a: UInt<1> output b: UInt<1> inst p1 of PassThrough inst p2 of PassThrough p1.a <= a p2.a <= a b <= p2.b ``` Previous output: ```verilog module Top( input a, output b ); PassThrough p1 ( .a (a), .b (/* unused */) ); PassThrough p2 ( .a (a), .b (b) ); endmodule ``` New output: ```verilog module Top( input a, output b ); PassThrough p2 ( .a (a), .b (b) ); endmodule ```
We've changed the modeling of InvalidValueOp to have side-effect so it's necessary to handle invalid values specially. Since InvalidValueOp has MemAlloc side-effects trait, this PR allows dead operations with known side-effects(Alloc/Read) to be removed.
uenoku
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This PR adds functionality to find and remove dead hierpaths and weak referencing annotations in IMDCE. Even though it's not explicitly defined yet, some annotations (for example OMIRTracker) are expected to be removed when annotation targets are dead. In many cases OMIRTracker is represented as non-local annotations associated with hierpaths which are users of inner symbols. So this PR imports some of InnerSymbolDCE logic into IMDCE and aggressively removes inner symbols.
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This PR backports several IMDCE improvements to delete dead instances associated with OMIRTrackers.