[InstCombine] enhance icmp with sub folds

[Allen]

Summary

The new IR with And removes a use of the input variable, which is better for analysis.

[goldstein.w.n]

llvm/test/Transforms/InstCombine/icmp-sub.ll

564

Can you split the tests into two commits so we can see the diff from the patch?

[goldstein.w.n]

The new IR with and removes a use of the input variable, which is better for analysis.

"and" -> And (otherwise it looks like the conjugation, not the operator.

[Allen]

1、Precommit the test
2、Add m_OneUse

[Allen]

In D145846#4200141, @goldstein.w.n wrote:

The new IR with and removes a use of the input variable, which is better for analysis.

"and" -> And (otherwise it looks like the conjugation, not the operator.

Done, thanks

llvm/test/Transforms/InstCombine/icmp-sub.ll

564

Done, I Precommit the test with D146268

[Allen]

ping ?

[nikic]

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

4100

Use ICmpInst::isEquality().

4102

Please add a vector test, this is probably going to crash. (Can use getScalarSizeInBits instead.)

4107

I.getPrediate() -> Pred.

llvm/test/Transforms/InstCombine/icmp-sub.ll

590

Missing commuted test case (negation on RHS), multi-use test case and negative tests (e.g. non-equality predicate).

[Allen]

address commet
1、Add more cases (also update on D146268)
2、update with getScalarSizeInBits and add related vector case
3、use ICmpInst::isEquality(Pred) to replace Pred == ICmpInst::ICMP_EQ
4、I.getPredicate() --> Pred

[nikic]

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

4100

isEquality() means "EQ" or "NE". You don't need to check for ICMP_NE separately.

llvm/test/Transforms/InstCombine/icmp-sub.ll

596

These end up not actually commuted due to complexity-based canonicalization. Grep for thwart complexity-based canonicalization for how to avoid it.

[Allen]

Address comment
1、delete the repeat ICMP_NE check, as isEquality() already include it
2、use "thwart complexity-based canonicalization" for commuted case

[nikic]

LGTM

[nikic]

Proof: https://alive2.llvm.org/ce/z/VNNPeG

[bcl5980]

How about this pattern ?
https://alive2.llvm.org/ce/z/Y-Po8g
Also reduce one usage but it works for any minuend.

[Allen]

https://github.com/llvm/llvm-project/issues/60818

In D145846#4266860, @bcl5980 wrote:

How about this pattern ?
https://alive2.llvm.org/ce/z/Y-Po8g
Also reduce one usage but it works for any minuend.

Yes, I think this case is similar, but it seems the llvm doesn't have the issue end-to-end for C source, https://godbolt.org/z/EYMo9bd9c.

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

4100

Apply your comment, thanks