[llvm] [SLP]Reduce number of alternate instruction, where possible (PR #128907)

[Alexey Bataev via llvm-commits]

alexey-bataev wrote:

> Hi @alexey-bataev
> 
> The following
> 
> ```
> clang -cc1 -triple x86_64-unknown-linux-gnu -emit-llvm -target-cpu x86-64 -O3 -vectorize-slp -fsanitize=alignment,shift-exponent,signed-integer-overflow -fsanitize-recover=shift-exponent bbi-105049.c
> ```
> 
> fails with
> 
> ```
> Instruction does not dominate all uses!
>   %43 = extractvalue { i32, i1 } %28, 0, !nosanitize !9
>   %39 = insertelement <4 x i32> %38, i32 %43, i64 1
> fatal error: error in backend: Broken module found, compilation aborted!
> ```
> 
> It starts happening with this patch, and it fails also with the latest version in [1008539](https://github.com/llvm/llvm-project/commit/10085390c6d4d0df04bf412f4c9ce7ebaaa5e3f3).
> 
> [bbi-105049.c.gz](https://github.com/user-attachments/files/19245264/bbi-105049.c.gz)

Fixed in bbd1bb40573dd5a36dc04af4ad307d6e16456f89

https://github.com/llvm/llvm-project/pull/128907