[llvm] [DAG] Add TRUNCATE_SSAT_S/U and TRUNCATE_USAT_U to canCreateUndefOrPoison (#152143) (PR #168809)

[Jerry Dang via llvm-commits]

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@@ -0,0 +1,80 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
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kuroyukiasuna wrote:

Progress so far: The select pattern tests showed different codegen in older LLVM(18.1.3). But the current (22.0.0git) assembly output is identical with/without this change. 
I've verified that freeze elimination occurs at the DAG level (node count: 9→8 in optimized legalized DAG via -debug-only=isel).

https://github.com/llvm/llvm-project/pull/168809