[llvm] [LoopIdiom] Support 'shift until less-than' idiom (PR #95002)

[Hari Limaye via llvm-commits]

hazzlim wrote:

> FYI @hazzlim, this may have introduced a regression in clang++.
> 
> Top of the tree clang is now crashing when compiling some of flang source. See:
> 
>     * https://lab.llvm.org/buildbot/#/builders/4/builds/631
> 
>     * https://lab.llvm.org/buildbot/#/builders/84/builds/335
> 
> 
> following assertion is hit in `(anonymous namespace)::LoopIdiomRecognize::runOnNoncountableLoop()` when compiling https://github.com/llvm/llvm-project/blob/main/flang/runtime/edit-input.cpp.
> 
> ```
> clang++: ../llvm/llvm/include/llvm/ADT/APInt.h:1503: uint64_t llvm::APInt::getZExtValue() const: Assertion `getActiveBits() <= 64 && "Too many bits for uint64_t"' failed.`
> ```

Thanks @jeanPerier - I can see what the issue is. I will revert + reland once I have a fix.

https://github.com/llvm/llvm-project/pull/95002