[clang] [llvm] [RFC][CodeGen] Add generic target feature checks for intrinsics (PR #201470)

[Shilei Tian via cfe-commits]

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@@ -25,6 +26,23 @@ TargetSubtargetInfo::TargetSubtargetInfo(
 
 TargetSubtargetInfo::~TargetSubtargetInfo() = default;
 
+bool TargetSubtargetInfo::isIntrinsicSupported(unsigned IntrinsicID,
+                                               const CallBase &CB) const {
+  StringRef RequiredFeatures = Intrinsic::getRequiredTargetFeatures(
+      static_cast<Intrinsic::ID>(IntrinsicID));
+
+  if (RequiredFeatures.empty())
+    return true;
+
+  if (RequiredFeatures == Intrinsic::CustomTargetFeatures)
+    return isIntrinsicSupportedByTarget(IntrinsicID, CB);
+
+  auto [It, Inserted] = IntrinsicSupportCache.try_emplace(IntrinsicID);
+  if (Inserted)
+    It->second = checkFeatureExpression(RequiredFeatures);
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shiltian wrote:

Right, but I see two issues:

- How do we represent the case where an intrinsic is always supported, but different subtargets use different manglings, or support different arguments? In that case, we'd need to explicitly introduce an extra target feature and add it to all subtargets.

- Wouldn't it also be more expensive if an intrinsic is not supported at all, since it adds an extra layer of checks?

https://github.com/llvm/llvm-project/pull/201470