[PATCH] D103788: [InstCombine] Eliminate casts to optimize ctlz operation

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

In D103788#2812375 <https://reviews.llvm.org/D103788#2812375>, @datta.nagraj wrote:

> Removed the hard cut off check. Please review Sir.

The hard check was definitely not right, but have you proven that a log2-of-bitwidth check is not necessary? The original Alive allowed for that kind of proof based on value type widths.
If we can't prove it, then I would include that check in this patch to be safe. 
I don't know what the motivating source code looks like. It seems unlikely that we would ever truncate to a type smaller than log2 of the wide type in real code, but we can't rule it out, so it still deserves a regression test.


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https://reviews.llvm.org/D103788