R5900: Use unsigned math for add/sub instructions #5252
Merged
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Signed overflow is undefined.
F0bes
approved these changes
Jan 6, 2022
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Description of Changes
For the interpreter and dynarec constant prop, this was causing different code to be generates at -O0 and -O3 in clang. As best I can tell, it's due to there being a possibility of signed overflow, thus the high bits are irrelevant. Except for us, when we're simulating a CPU.
"Bad" code was only generated in clang, msvc and gcc were fine.
Case which prompted this was Juiced 2, but there may be others.
Rationale behind Changes
Getting rid of undefined behaviour and fixing game crashes, yay.
Suggested Testing Steps
Quick testing in interpreter and dynarec to make sure nothing was relying on this broken behaviour. Preferably with clang.