[llvm] [X86] Use generic CPU tuning when tune-cpu is empty (PR #83631)

[Phoebe Wang via llvm-commits]

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@@ -252,7 +252,7 @@ void X86Subtarget::initSubtargetFeatures(StringRef CPU, StringRef TuneCPU,
     CPU = "generic";
 
   if (TuneCPU.empty())
-    TuneCPU = "i586"; // FIXME: "generic" is more modern than llc tests expect.
+    TuneCPU = Is64Bit ? "x86-64" : "i586";
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phoebewang wrote:

Did you check the lit tests? I found some 64-bit test changes in your previous patch. So I assume they are affected by this change too.

https://github.com/llvm/llvm-project/pull/83631