[Support] Investigate making KnownBits saturated add/sub implementations optimal

[RKSimon]

llvm-project/llvm/unittests/Support/KnownBitsTest.cpp

Lines 429 to 460 in 44be5a7

	testBinaryOpExhaustive(
	[](const KnownBits &Known1, const KnownBits &Known2) {
	return KnownBits::sadd_sat(Known1, Known2);
	},
	[](const APInt &N1, const APInt &N2) -> std::optional<APInt> {
	return N1.sadd_sat(N2);
	},
	checkCorrectnessOnlyBinary);
	testBinaryOpExhaustive(
	[](const KnownBits &Known1, const KnownBits &Known2) {
	return KnownBits::uadd_sat(Known1, Known2);
	},
	[](const APInt &N1, const APInt &N2) -> std::optional<APInt> {
	return N1.uadd_sat(N2);
	},
	checkCorrectnessOnlyBinary);
	testBinaryOpExhaustive(
	[](const KnownBits &Known1, const KnownBits &Known2) {
	return KnownBits::ssub_sat(Known1, Known2);
	},
	[](const APInt &N1, const APInt &N2) -> std::optional<APInt> {
	return N1.ssub_sat(N2);
	},
	checkCorrectnessOnlyBinary);
	testBinaryOpExhaustive(
	[](const KnownBits &Known1, const KnownBits &Known2) {
	return KnownBits::usub_sat(Known1, Known2);
	},
	[](const APInt &N1, const APInt &N2) -> std::optional<APInt> {
	return N1.usub_sat(N2);
	},
	checkCorrectnessOnlyBinary);

Investigate if we can make the implementation optimal (checkOptimalityBinary)

[llvmbot]

Hi!

This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:

1. In the comments of the issue, request for it to be assigned to you.
2. Fix the issue locally.
3. Run the test suite locally. Remember that the subdirectories under test/ create fine-grained testing targets, so you can e.g. use make check-clang-ast to only run Clang's AST tests.
4. Create a Git commit.
5. Run git clang-format HEAD~1 to format your changes.
6. Open a pull request to the upstream repository on GitHub. Detailed instructions can be found in GitHub's documentation.

If you have any further questions about this issue, don't hesitate to ask via a comment in the thread below.

[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Simon Pilgrim (RKSimon)

https://github.com/llvm/llvm-project/blob/44be5a7fdc20a7f90d63dc18699a470e900bd3ba/llvm/unittests/Support/KnownBitsTest.cpp#L429-L460

Investigate if we can make the implementation optimal (checkOptimalityBinary)

[Mabwas]

i would love to work on this issue. can it be assigned to me please?

[Mabwas]

Thank you for assigning me the project. I will start working on it as soon as possible and will get back to you.

…

On Sat, 9 Mar 2024, 12:35 pm Nikita Popov, ***@***.***> wrote: Assigned #84213 <#84213> to @Mabwas <https://github.com/Mabwas>. — Reply to this email directly, view it on GitHub <#84213 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/BFN2YMKCFXU2T2E6IBENX53YXLXYDAVCNFSM6AAAAABEJQV2LCVHI2DSMVQWIX3LMV45UABCJFZXG5LFIV3GK3TUJZXXI2LGNFRWC5DJN5XDWMJSGA3DEOJYGM2DSMI> . You are receiving this because you were assigned.Message ID: ***@***.***>

[RKSimon]

This looks like it will be addressed in #110329

[goldsteinn]

Oh, I'm sorry I didn't realize this was already assigned. @mabwar, based on feedback from reviewers #110329 will be split apart. If you would like to take over the add/sat part of it and handle getting it through review, ping back. Ill hold it for the next few days.

[goldsteinn]

@Mabwas

[RKSimon]

@goldsteinn I think @Mabwas has been given enough time to respond - feel free to commandeer this issue