[PATCH] D153148: [InstCombine] Fold `(-1 + A) & B` into `A ? 0 : B` where A is effectively a bool

[Yingwei Zheng via Phabricator via llvm-commits]

dtcxzyw added inline comments.


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Comment at: llvm/test/Transforms/InstCombine/binop-cast.ll:302
 
 ; Negative test of and_add_bool_to_select
 define i32 @and_add_bool_no_fold(i32 %y) {
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dtcxzyw wrote:
> nikic wrote:
> > This isn't a negative test?
> It was added as a negative test since @goldstein.w.n thought it should be a regression.
> However, I tested the inst seq on some backends and found that `icmp; select` seems to get better codegen.
> 
> x86-64: https://godbolt.org/z/jv9v9xTMT
> riscv64: https://godbolt.org/z/zTbbnn9x4
> riscv64 (sifive-u74 with SFB opt): https://godbolt.org/z/aKjEs5n1P (`icmp; select` only costs 2 cycles with SFB)
> aarch64: https://godbolt.org/z/eK6xWKnrb
> 
> I think the pattern `select i1 %x, i32 %y, i32 0` is more likely to get better codegen.
> 
@goldstein.w.n Any more comments here? I think it should not be a negative test.



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  https://reviews.llvm.org/D153148/new/

https://reviews.llvm.org/D153148