[llvm] Implement areInlineCompatible for SystemZ using feature bitset (PR #132976)

[Ulrich Weigand via llvm-commits]

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@@ -422,6 +422,20 @@ bool SystemZTTIImpl::isLSRCostLess(const TargetTransformInfo::LSRCost &C1,
              C2.ScaleCost, C2.SetupCost);
 }
 
+bool SystemZTTIImpl::areInlineCompatible(const Function *Caller,
+                                         const Function *Callee) const {
+  const TargetMachine &TM = getTLI()->getTargetMachine();
+
+  const FeatureBitset &CallerBits =
+      TM.getSubtargetImpl(*Caller)->getFeatureBits();
+  const FeatureBitset &CalleeBits =
+      TM.getSubtargetImpl(*Callee)->getFeatureBits();
+
+  // Check that target features from the callee are subset or
+  // equal to the caller's features.
+  return (CalleeBits == CallerBits) || (CalleeBits < CallerBits);
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uweigand wrote:

Inlining when the bitsets are the same would certainly be correct, and we might want to do that as an interim solution.  But is that actually any different from the current (default) behavior?

https://github.com/llvm/llvm-project/pull/132976