[SLP]Fix PR55734: SLP vectorizer's reduce_and formation introduces poison.

[ABataev]

Summary

Need either follow the original order of the operands for bool logical
ops, or emit freeze instruction to avoid poison propagation.

[ABataev]

Rebase and use isGuaranteedNotToBePoison as an extra check

[ABataev]

Rebase

[ABataev]

Ping!

[spatel]

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

11286

This could use a comment to describe the patterns/logic.

IIUC, we want to create a bool logic op like:

select i1 LHS, i1 RHS, i1 false ; logical and

If we have original code like this:

RedOp1 = select i1 ?, i1 LHS, i1 false
RedOp2 = select i1 RHS, i1 ?, i1 false

Then, we swap LHS/RHS to create a new op that matches the poison semantics of the original code.

If we have original code like this and both values could be poison:

RedOp1 = select i1 ?, i1 LHS, i1 false
RedOp2 = select i1 ?, i1 RHS, i1 false

Then, we must freeze LHS in the new op. Can we manufacture a test for this 2nd path? I don't think there's any coverage for that path in the current test diffs.

[ABataev]

Reworked addition of the reduction. For logical ops, reduction result is added as a first operand,
it is safe to use it as an LHS in scalar logical ands/ors.
For others, it is added as a last operand.

[spatel]

llvm/test/Transforms/SLPVectorizer/X86/reduction-logical.ll

311–312

The updated patch does not fix the bug?
https://alive2.llvm.org/ce/z/YYaTVw