[llvm] [GlobalISel] Fold G_CTTZ if possible (PR #86224)

[Matt Arsenault via llvm-commits]

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@@ -256,10 +256,16 @@ MachineInstrBuilder CSEMIRBuilder::buildInstr(unsigned Opc,
       return buildFConstant(DstOps[0], *Cst);
     break;
   }
-  case TargetOpcode::G_CTLZ: {
+  case TargetOpcode::G_CTLZ:
+  case TargetOpcode::G_CTTZ: {
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arsenm wrote:

We should probably also handle the _ZERO_UNDEF variants 

https://github.com/llvm/llvm-project/pull/86224