[llvm] [GlobalISel] Add G_ABS computeKnownBits, add ComputeKnownBitsCache assertion to computeNumSignBits (PR #154413)

[David Green via llvm-commits]

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@@ -1781,7 +1789,7 @@ static unsigned computeNumSignBitsFromRangeMetadata(const GAnyLoad *Ld,
                   CR.getSignedMax().getNumSignBits());
 }
 
-unsigned GISelValueTracking::computeNumSignBits(Register R,
+unsigned GISelValueTracking::computeNumSignBitsImpl(Register R,
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davemgreen wrote:

Should all the calls to computeNumSignBits in this function now be computeNumSignBitsImpl too? (I don't think I can comment on that line directly in github).
Also the 3 in AMDGPUTargetLowering::computeNumSignBitsForTargetInstr.
Maybe the ones in computeNumSignBitsMin too.

https://github.com/llvm/llvm-project/pull/154413