[llvm] [NVPTX] Improve support for {ex2,lg2}.approx (PR #120519)

[Alex MacLean via llvm-commits]

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@@ -145,6 +145,7 @@ def noPTXASUnreachableBug : Predicate<"!Subtarget->hasPTXASUnreachableBug()">;
 def doF32FTZ : Predicate<"useF32FTZ()">;
 def doNoF32FTZ : Predicate<"!useF32FTZ()">;
 def doRsqrtOpt : Predicate<"doRsqrtOpt()">;
+def useApproxLog2 : Predicate<"useApproxLog2()">;
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AlexMaclean wrote:

Is this predicate required? Won't all Log2 nodes be removed during legalization if useApproxLog2 is not enabled?

https://github.com/llvm/llvm-project/pull/120519