[GR-77075] Add instruction rewriting support for stack values. - #14333
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…uctions when returning from block Adds rewrite rules of the form: store.stackvalue(k), pop * k - 1, return -> return Essentially, when the result of a block is returned, we can skip the cleanup instructions since the frame will be thrown away.
This is a non-functional change necessary to properly remap childBci fields.
Adds rewrite rules of the form:
load.stackvalue(n - 1) * n, X, pop * n -> X (void X consumes n values)
load.stackvalue(n - 1) * n, X, store.stackvalue(n), pop * (n - 1) -> X (non-void X consumes n == k stack values)
load.stackvalue(n - 1) * n, X, store.stackvalue(k), pop * (k - 1) -> X, store.stackvalue(k - n), pop * (k - n - 1) (non-void X consumes n < k stack values)
This change requires limited support for REPLACE sections that replace 1 instruction with 1 instruction in order to replace the store.stackvalue instruction in the last pattern.
Since BCIs into instructions are disallowed, this limitation makes replacement safe without adding full support to check for ambiguous BCIs.
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Adds some new rewrite rules and the rewrite machinery to support them (immediate matching, REPLACE sections).
Also refactors the builder to keep operation stack entries on stack until after instruction emission, so that we can rewrite child bci's stored in the current operation stack entry.
New rewrite rules:
In text: if the result of a block is returned, we can skip the cleanup instructions since the frame will be thrown away.
In text: if X consumes some stack values from the top of stack, and then we pop those values, let X consume them directly.