[llvm] [ARM] Emit a warning when the hard-float ABI is enabled but can't be used. (PR #111334)

[Peter Smith via llvm-commits]

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@@ -791,7 +791,9 @@ ARMTargetLowering::ARMTargetLowering(const TargetMachine &TM,
       setAllExpand(MVT::f32);
     if (!Subtarget->hasFP64())
       setAllExpand(MVT::f64);
-  }
+  } else if (TM.Options.FloatABIType == FloatABI::Hard)
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smithp35 wrote:

I'm happy to follow @ostannard 's choice here. Fixing up tests to specify the correct flags is a good thing. 

My concern last year, apologies I've forgotten a lot of the details, was if these represent any use cases we may encounter with clang, possibly using some target attributes or with LTO. However after doing our best to rule this out, we can give it  a go and see if we hit anything we didn't think about beforehand.

https://github.com/llvm/llvm-project/pull/111334