[llvm] Metadata: Optimize metadata queries (PR #70700)

[Duncan P. N. Exon Smith via llvm-commits]

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@@ -303,8 +303,14 @@ class Instruction : public User,
   /// Get the metadata of given kind attached to this Instruction.
   /// If the metadata is not found then return null.
   MDNode *getMetadata(unsigned KindID) const {
-    if (!hasMetadata()) return nullptr;
-    return getMetadataImpl(KindID);
+    // Handle 'dbg' as a special case since it is not stored in the hash table.
+    if (KindID == LLVMContext::MD_dbg) {
+      return DbgLoc.getAsMDNode();
+    }
+    if (hasMetadataOtherThanDebugLoc()) {
+      return getMetadataImpl(KindID);
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dexonsmith wrote:

Note that `Value::hasMetadata()` is a protected member, accessing a bit stored on Value that caches whether anything is in the DenseMap stored in the LLVMContext.

https://github.com/llvm/llvm-project/pull/70700