[PATCH] D142234: [ConstantRange] Handle Intrinsic::ctlz

[Antonio Frighetto via Phabricator via llvm-commits]

antoniofrighetto added inline comments.


================
Comment at: llvm/test/Analysis/LazyValueAnalysis/lvi-for-ctlz.ll:1
+; RUN: opt < %s -passes=jump-threading -print-lvi-after-jump-threading -disable-output 2>&1 | FileCheck %s
+
----------------
nikic wrote:
> nikic wrote:
> > Having an IR test is fine, but please do not test LVI debug output. Just check the resulting IR change using update_test_checks.py.
> I don't think that as written, these tests really test anything. There needs to be a comparison involving the ctlz that can be folded away, or similar.
I feel like a suitable test could be the following one:
```
int lol(int b) {
    if (b < 65536) {
        int n = __builtin_clz(b);
        if (n < 8)
    	    return 0;
        else
            return 1;
   }
   return 2;
}
```
which now could be simplified in a `return (b < 65536) ? 1 : 2;`. However, as far as I understand this, CVP needs to be extended as well in order to be able to obtain the above constant folding. Is that correct?


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  https://reviews.llvm.org/D142234/new/

https://reviews.llvm.org/D142234