[llvm] [CodeGen] Emit a more efficient magic number multiplication for exact udivs (PR #87161)

[via llvm-commits]

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@@ -6141,6 +6138,68 @@ static SDValue BuildExactSDIV(const TargetLowering &TLI, SDNode *N,
   return DAG.getNode(ISD::MUL, dl, VT, Res, Factor);
 }
 
+/// Given an exact UDIV by a constant, create a multiplication
+/// with the multiplicative inverse of the constant.
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AtariDreams wrote:

> Is there a reference for what this is doing somewhere?



> Is there a reference for what this is doing somewhere?

yes. hacker's delight, but this matches exactly what SDiv does too, since the algorithm is the same.

https://github.com/llvm/llvm-project/pull/87161