[do not merge] work-in-progress dead code elimination #348
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| let deadAssignment' := deadAssignment used_after in | ||
| match s with | ||
| | SIf c s1 s2 => SIf c (deadAssignment' s1) (deadAssignment' s2) | ||
| | SLoop s1 c s2 => SLoop s1 c s2 (* loops are scary so skipping this case for now *) |
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Hehe I agree that they are scary 😉 But they will also be important, because most loops contain something like i = i + 1, and UseImmediate will turn this into an Addi, creating an unused temporary for the value 1.
I would start by studying the SLoop case of live, and then try using a similar pattern as you used in the SSeq case of deadAssignment.
| | SSeq s1 s2 => | ||
| let s2' := deadAssignment' s2 in | ||
| let s1_used_after := live s2' used_after in | ||
| SSeq (deadAssignment s1_used_after s1) (s2') |
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Suggested change
| SSeq (deadAssignment s1_used_after s1) (s2') | |
| SSeq (deadAssignment s1_used_after s1) s2' |
| | CondNez x => [x] | ||
| end. | ||
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| Fixpoint live(s: stmt var)(used_after: list var): list var := |
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This one should eventually go into its own file, abstract over the type of variables and their boolean equality, and be shared between this phase and the register allocator.
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Work on implementing a compiler phase for replacing SSet's, SLit's and SOp's that target variables that are unread later in the function (or not live) with SSkip. Currently first pass of implementation is done, still need to work on proof of correctness.
Attached are screenshots of diffs of assembly code in compilerExamples/deadAssExample.v