[llvm] Optimize count leading ones if promoted type (PR #99591)

[Matt Arsenault via llvm-commits]

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@@ -2298,8 +2298,29 @@ static bool despeculateCountZeros(IntrinsicInst *CountZeros,
   if (match(CountZeros->getOperand(1), m_One()))
     return false;
 
-  // If it's cheap to speculate, there's nothing to do.
   Type *Ty = CountZeros->getType();
+  EVT VTy = TLI->getValueType(*DL, Ty);
+
+  // do not despeculate if we have (ctlz (xor op -1)) if the operand is
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arsenm wrote:

Capitalize comment. Also I guess given the vector check above, the vector case doesn't matter? 

https://github.com/llvm/llvm-project/pull/99591