[llvm] [AArch64] Fall back to SelectionDAG ISel if GISel is not feasible. (PR #196343)

[Sander de Smalen via llvm-commits]

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@@ -613,7 +599,14 @@ bool AArch64CallLowering::fallBackToDAGISel(const MachineFunction &MF) const {
       Attrs.hasStreamingCompatibleInterface())
     return true;
 
-  return false;
+  // Enable GlobalISel when feasible and when:
+  // * Forced by option to enable gisel
+  // * The current opt-level is supported by EnableGlobalISelAtO
+  // * The function is an optnone function.
+  auto OptLevel = MF.getTarget().getOptLevel();
+  return !(getCGPassBuilderOption().EnableGlobalISelOption.value_or(false) ||
+           static_cast<unsigned>(OptLevel) <= TM.getEnableGlobalISelAtO() ||
+           F.hasOptNone());
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sdesmalen-arm wrote:

Yes, same here, I wrote it like this on purpose because it's a bit easier to reason about.

https://github.com/llvm/llvm-project/pull/196343