[clang] [llvm] [Driver][RISCV] Support the new `-mtune` syntax with tuning feature string (PR #196653)

[Pengcheng Wang via cfe-commits]

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@@ -169,6 +169,12 @@ void riscv::getRISCVTargetFeatures(const Driver &D, const llvm::Triple &Triple,
     Features.push_back("+unaligned-vector-mem");
   }
 
+  SmallVector<std::string, 4> TuneFeatures;
+  if (!riscv::getRISCVTuneCPU(D, Args, &TuneFeatures))
+    return;
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wangpc-pp wrote:

If we return early here, then we won't run to `handleTargetFeaturesGroup` below. Does this mean we can't specify features in `m_riscv_Features_Group` if `getRISCVTuneCPU` fails?

https://github.com/llvm/llvm-project/pull/196653