Optimizations to reduce unnecessary copies

MerlinVR / UdonSharp

An experimental compiler for compiling C# to Udon assembly

MIT License

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Optimizations to reduce unnecessary copies #18

Closed bdunderscore closed 4 years ago

bdunderscore commented 4 years ago

This change introduces two related optimization to reduce unnecessary copies:

We now opportunistically avoid excess copies between the result of certain binary and function invocation operations and the assignee of an assignment expression. Note that there are some expressions (eg unary negation or minus) that are not yet covered by this change.
We avoid copying the left-hand-side of a binary operation unless the right-hand side actually has a side effect that may mutate the LHS value.

As part of this, we also fix some issues where function call parameters or array expressions would not respect proper order of operations.

Fixes: #15

bdunderscore commented 4 years ago

Note to self: Before merging, I need to audit to make sure that in cases where (implicit) type conversion is required, we don't attempt to use the same heap variable for the pre-conversion type, to avoid unnecessary extra heap allocations.

bdunderscore commented 4 years ago

Verified that casts work as intended, should be ready for review now.

MerlinVR commented 4 years ago

👍 will do, thanks!

bdunderscore commented 4 years ago

Found a bug in array indexing that could result in unnecessary copies, will add some more commits to fix shortly.

bdunderscore commented 4 years ago

Regression:

uint x;
x <<= 1;

seems to fail to compile now. Will update later tonight.

bdunderscore commented 4 years ago

@Merlin-san I've backed out the const conversion changes from this branch. It's looking like the const conversion stuff will be more complicated than I thought, requiring interactions with function call inference, so it's probably best to leave it until there's an IR as you suggested.